Custom HTTP tools an administrator defines

A row in custom_tools becomes a ToolDef like any built-in, offered beside
the thirteen. The registry had to stop being an import-time constant for
that: `resolve_tools` now returns the schemas *and* the runners together,
carried to the loop on the ToolContext.

That closes a hole on the way. `run_tool` looked names up in the global
REGISTRY with no reference to what had been offered, so a model naming a
tool its chat was gated out of -- a family switched off, a permission the
reader lacks -- had it run anyway. The resolved set is now authoritative.

Arguments come from a model, so an argument may fill a hole but never move
the target: the scheme and host of a URL template are literal, values are
escaped for where they land, and the origin is pinned afterwards. Every
redirect hop is checked the way services/fetch.py checks one, and the
secret is dropped if a hop leaves the origin it was issued for.

Also fixes the tool-activity block claiming every library tool had
"searched the web", which it has done since the second family landed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "lembas"
-version = "0.3.1"
+version = "0.4.0"
 description = "LLeMbas - a Middle-earth themed web UI for OpenAI-compatible LLM endpoints"
 readme = "README.md"
 requires-python = ">=3.11"

src/lembas/__init__.py

@@ -1,3 +1,3 @@
 """LLeMbas - a Middle-earth themed web UI for OpenAI-compatible LLM endpoints."""
 
-__version__ = "0.3.1"
+__version__ = "0.4.0"

src/lembas/api/admin_models.py

@@ -24,15 +24,23 @@ router = APIRouter(tags=["admin-models"])
 # these are an administrator's assertion.
 PROTOCOL_CAPABILITIES = ("reasoning", "vision", "tools")
 
-# Which built-in tools this model is given. Distinct from the above: `tools` is
+# Which tools this model is given. Distinct from the above: `tools` is whether a
-# whether a tools array may be sent at all, these are what goes in it. Every one
+# tools array may be sent at all, these are what goes in it. Every one of them is
-# of them is meaningless unless `tools` is on.
+# meaningless unless `tools` is on.
+#
+# The last two are gates rather than single tools: one covers every custom HTTP
+# tool an administrator has defined, the other every MCP server. Which of those
+# a particular person gets is the tool's own group list, not a flag here -- a
+# server can advertise forty tools, and a model page listing all of them is a
+# page nobody can read.
 TOOL_CAPABILITIES = (
     ("tool_web_search", "Web search"),
     ("tool_knowledge", "Knowledge"),
     ("tool_notes", "Notes"),
     ("tool_memory", "Memory"),
     ("tool_skills", "Skills"),
+    ("tool_custom", "Custom tools"),
+    ("tool_mcp", "MCP servers"),
 )
 
 CAPABILITIES = PROTOCOL_CAPABILITIES + tuple(key for key, _ in TOOL_CAPABILITIES)

src/lembas/api/admin_prompts.py

@@ -29,15 +29,20 @@ router = APIRouter(prefix="/admin/prompts", tags=["admin-prompts"])
 SAMPLE_DOCUMENTS = "report.pdf, notes.txt"
 
 
-def _families_of(names: list[str]) -> list[str]:
+def _families_of(db: Db, names: list[str]) -> list[str]:
-    """Keep only real family names, in the registry's order."""
+    """Keep only real family names, in the registry's order.
+
+    Read from the database rather than the constant: a family can belong to an
+    administrator-defined tool, and one the preview cannot name is one whose
+    guidance cannot be checked here.
+    """
     wanted = set(names)
-    return [family for family in tools_service.FAMILIES if family in wanted]
+    return [family for family in tools_service.families(db) if family in wanted]
 
 
-def _tool_names(families: list[str]) -> str:
+def _tool_names(db: Db, families: list[str]) -> str:
     return ", ".join(
-        name for name, tool in tools_service.REGISTRY.items() if tool.family in families
+        name for name, tool in tools_service.registry(db).items() if tool.family in families
     )
 
 
@@ -67,7 +72,7 @@ def _variables(
     values.update(
         {
             "model_name": model_name,
-            "tool_names": _tool_names(families),
+            "tool_names": _tool_names(db, families),
             "memories": memories_service.block(db, user) if "memory" in families else "",
             "skills": skills_service.index_block(db, user) if "skills" in families else "",
             "knowledge_bases": bases if "knowledge" in families else "",
@@ -89,7 +94,7 @@ def _field_context(db: Db, key: str, *, value: str, overridden: bool) -> dict:
 async def prompts_page(request: Request, db: Db, user: AdminUser, saved: bool = False):
     stored = prompts_service.stored(db)
     models = chat_service.available_models(db, user)
-    families = list(tools_service.FAMILIES)
+    families = list(tools_service.families(db))
 
     return render(
         request,
@@ -115,7 +120,7 @@ async def prompts_page(request: Request, db: Db, user: AdminUser, saved: bool =
             "models": models,
             "families": families,
             "registry": sorted(
-                tools_service.REGISTRY.values(), key=lambda t: (t.family, t.name)
+                tools_service.registry(db).values(), key=lambda t: (t.family, t.name)
             ),
             "max_harness_chars": settings_store.get(
                 db, "max_harness_chars", key=settings_store.PROMPTS
@@ -164,7 +169,7 @@ async def preview(request: Request, db: Db, user: AdminUser):
     """
     form = await request.form()
     overrides = _submitted(db, form)
-    families = _families_of([str(value) for value in form.getlist("preview_family")])
+    families = _families_of(db, [str(value) for value in form.getlist("preview_family")])
     model_name = str(form.get("preview_model") or "")
     bases = str(form.get("preview_bases") or "").strip()
     documents = str(form.get("preview_documents") or "").strip()

src/lembas/api/admin_tools.py

@@ -0,0 +1,415 @@
+"""Administration for the tools an administrator defines.
+
+List-plus-detail, like `/admin/models` and for the same reason: a tool has
+fifteen fields and a page that renders fifteen fields per row is unusable. The
+list is compact and searchable; the whole form lives at `/admin/tools/{id}/edit`.
+
+Validation reports back into the form rather than raising a 422. The fields here
+are a JSON schema, a URL template and a secret; getting one wrong is normal, and
+losing the other fourteen because of it is not acceptable. So a rejected save
+re-renders the form from what was submitted, with the reason.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import re
+from datetime import UTC, datetime
+
+from fastapi import APIRouter, HTTPException, Request, Response, status
+from fastapi.responses import RedirectResponse
+from sqlalchemy import func, select
+
+from lembas.api.deps import AdminUser, Db
+from lembas.db.models import (
+    RESPONSE_JSON,
+    RESPONSE_MODES,
+    RESPONSE_RAW,
+    RESPONSE_TEXT,
+    SECRET_NONE,
+    SECRET_PLACEMENTS,
+    CustomTool,
+    Group,
+)
+from lembas.services import custom_tools
+from lembas.services import prompts as prompts_service
+from lembas.services import tools as tools_service
+from lembas.services.crypto import UNCHANGED_SENTINEL, decrypt, keep_or_replace, mask
+from lembas.web.templating import render
+
+log = logging.getLogger(__name__)
+
+router = APIRouter(tags=["admin-tools"])
+
+PAGE_SIZE = 40
+
+# The slug is the function name sent to the endpoint, so it is bound by the
+# charset those accept, and it is half of this tool's prompt-fragment key, so it
+# is bound by that pattern too. The intersection is this.
+SLUG_PATTERN = re.compile(r"^[a-z0-9][a-z0-9_-]{0,47}$")
+
+FILTERS: dict[str, tuple[str, object]] = {
+    "all": ("All", lambda t: True),
+    "enabled": ("Enabled", lambda t: t.enabled),
+    "disabled": ("Disabled", lambda t: not t.enabled),
+    "restricted": ("Restricted", lambda t: not t.public),
+}
+
+RESPONSE_LABELS = (
+    (RESPONSE_TEXT, "Text — HTML reduced to prose"),
+    (RESPONSE_JSON, "JSON — parsed, narrowed by the path below"),
+    (RESPONSE_RAW, "Raw — exactly as it arrived"),
+)
+
+SECRET_LABELS = (
+    (SECRET_NONE, "None — this endpoint needs no credential"),
+    ("bearer", "Bearer token in a header"),
+    ("header", "The header named below, verbatim"),
+    ("query", "A query parameter named below"),
+)
+
+
+def _tool(db: Db, tool_id: str) -> CustomTool:
+    tool = db.get(CustomTool, tool_id)
+    if tool is None:
+        raise HTTPException(status.HTTP_404_NOT_FOUND, "That tool no longer exists.")
+    return tool
+
+
+def _ordered(db: Db) -> list[CustomTool]:
+    return list(db.scalars(select(CustomTool).order_by(CustomTool.position, CustomTool.slug)))
+
+
+def _back(message: str = "") -> Response:
+    target = f"/admin/tools?saved={message}" if message else "/admin/tools"
+    return RedirectResponse(target, status_code=status.HTTP_303_SEE_OTHER)
+
+
+# --- Form <-> row ------------------------------------------------------------
+def _headers_text(headers: dict) -> str:
+    return "\n".join(f"{name}: {value}" for name, value in (headers or {}).items())
+
+
+def _parse_headers(text: str) -> dict[str, str]:
+    """One `Name: value` per line. Blank lines and lines with no colon are dropped."""
+    out: dict[str, str] = {}
+    for line in (text or "").splitlines():
+        name, _, value = line.partition(":")
+        if name.strip() and _:
+            out[name.strip()] = value.strip()
+    return out
+
+
+def _number(raw: str, *, default: int, low: int, high: int) -> int:
+    text = str(raw or "").strip()
+    if not text.lstrip("-").isdigit():
+        return default
+    return min(max(int(text), low), high)
+
+
+def _populate(tool: CustomTool, form) -> None:
+    """Copy a submitted form onto a row (or a draft of one).
+
+    Checkboxes are read by key presence: FastAPI cannot tell `x=` from an absent
+    `x`, and an absent one is exactly what an unticked box sends.
+    """
+    tool.name = str(form.get("name") or "").strip()[:120]
+    tool.description = str(form.get("description") or "").strip()
+    tool.guidance = str(form.get("guidance") or "").replace("\r\n", "\n").strip()
+    tool.method = str(form.get("method") or "GET").strip().upper()
+    tool.url_template = str(form.get("url_template") or "").strip()[:1000]
+    tool.body_template = str(form.get("body_template") or "").replace("\r\n", "\n")
+    tool.headers_json = _parse_headers(str(form.get("headers") or ""))
+
+    placement = str(form.get("secret_placement") or SECRET_NONE)
+    tool.secret_placement = placement if placement in SECRET_PLACEMENTS else SECRET_NONE
+    tool.secret_name = str(form.get("secret_name") or "Authorization").strip()[:120]
+
+    mode = str(form.get("response_mode") or RESPONSE_TEXT)
+    tool.response_mode = mode if mode in RESPONSE_MODES else RESPONSE_TEXT
+    tool.response_path = str(form.get("response_path") or "").strip()[:300]
+
+    tool.max_chars = _number(
+        form.get("max_chars"),
+        default=8000,
+        low=custom_tools.MIN_CHARS,
+        high=custom_tools.MAX_CHARS,
+    )
+    tool.timeout = _number(
+        form.get("timeout"),
+        default=20,
+        low=custom_tools.MIN_TIMEOUT,
+        high=custom_tools.MAX_TIMEOUT,
+    )
+    tool.position = _number(form.get("position"), default=tool.position or 0, low=0, high=999)
+
+    tool.allow_private = "allow_private" in form
+    tool.enabled = "enabled" in form
+    tool.public = "public" in form
+
+
+def _problem(db: Db, tool: CustomTool, form, *, existing_id: str = "") -> str:
+    """Why this cannot be saved, or an empty string."""
+    if not tool.name:
+        return "A tool needs a name."
+
+    slug = str(form.get("slug") or "").strip().lower()
+    if not SLUG_PATTERN.match(slug):
+        return (
+            "The identifier must be lowercase letters, digits, hyphens or "
+            "underscores, start with a letter or digit, and be at most 48 "
+            "characters. It is the name the model calls."
+        )
+    if slug in tools_service.REGISTRY:
+        return f"“{slug}” is the name of a built-in tool. Choose another."
+    clash = db.scalar(select(CustomTool).where(CustomTool.slug == slug))
+    if clash is not None and clash.id != existing_id:
+        return f"There is already a tool called “{slug}”."
+    tool.slug = slug
+
+    if tool.method not in custom_tools.ALLOWED_METHODS:
+        return f"{tool.method} is not a method this can send."
+
+    raw = str(form.get("parameters") or "").strip() or '{"type": "object", "properties": {}}'
+    try:
+        parameters = json.loads(raw)
+    except json.JSONDecodeError as exc:
+        return f"The parameters are not valid JSON: {exc}"
+    if not isinstance(parameters, dict) or parameters.get("type") != "object":
+        return 'The parameters must be a JSON object whose "type" is "object".'
+    tool.parameters_json = parameters
+
+    # The same check the runner makes, so a template that could never be called
+    # is refused here rather than at the first call.
+    try:
+        custom_tools.fill_url(custom_tools.spec_from(tool), {})
+    except Exception as exc:  # noqa: BLE001 - any refusal is a message for the form
+        return str(getattr(exc, "message", exc))
+
+    return ""
+
+
+def _detail(request: Request, db: Db, tool: CustomTool, *, is_new: bool, error: str = "", **extra):
+    key = f"tool.custom_{tool.slug}" if tool.slug else ""
+    return render(
+        request,
+        "admin/tool_detail.html",
+        {
+            "tool": tool,
+            "is_new": is_new,
+            "error": error,
+            "groups": list(db.scalars(select(Group).order_by(Group.name))),
+            "selected_groups": extra.pop(
+                "selected_groups", {group.id for group in (tool.groups if tool.id else [])}
+            ),
+            "headers_text": extra.pop("headers_text", _headers_text(tool.headers_json)),
+            "parameters_text": extra.pop(
+                "parameters_text", json.dumps(tool.parameters_json or {}, indent=2)
+            ),
+            "masked": mask(decrypt(tool.secret_encrypted)) if tool.secret_encrypted else "",
+            "unchanged": UNCHANGED_SENTINEL,
+            "methods": custom_tools.ALLOWED_METHODS,
+            "response_modes": RESPONSE_LABELS,
+            "secret_placements": SECRET_LABELS,
+            "prompt_key": key,
+            "prompt_overridden": key in prompts_service.stored(db),
+            **extra,
+        },
+    )
+
+
+# --- The list ----------------------------------------------------------------
+@router.get("/admin/tools")
+async def tools_page(
+    request: Request,
+    db: Db,
+    user: AdminUser,
+    saved: str = "",
+    q: str = "",
+    filter: str = "all",
+    page: int = 1,
+):
+    everything = _ordered(db)
+    predicate = FILTERS.get(filter, FILTERS["all"])[1]
+    needle = q.strip().lower()
+    matching = [
+        tool
+        for tool in everything
+        if predicate(tool)
+        and (not needle or needle in tool.slug.lower() or needle in (tool.name or "").lower())
+    ]
+
+    pages = max(1, -(-len(matching) // PAGE_SIZE))
+    page = max(1, min(page, pages))
+    start = (page - 1) * PAGE_SIZE
+
+    return render(
+        request,
+        "admin/tools.html",
+        {
+            "tools": matching[start : start + PAGE_SIZE],
+            "total": len(everything),
+            "matched": len(matching),
+            "page": page,
+            "pages": pages,
+            "page_start": start,
+            "counts": {
+                key: sum(1 for tool in everything if rule(tool))
+                for key, (_label, rule) in FILTERS.items()
+            },
+            "filters": {key: label for key, (label, _rule) in FILTERS.items()},
+            "active_filter": filter if filter in FILTERS else "all",
+            "q": q,
+            "saved": saved,
+        },
+    )
+
+
+# Registered before /{tool_id}: FastAPI matches in registration order, so with
+# the parameterised route first "new" is captured as an id and the handler 404s
+# on a tool that does not exist. This has already been a bug once, in
+# /admin/models.
+@router.get("/admin/tools/new")
+async def new_tool_page(request: Request, db: Db, user: AdminUser):
+    draft = CustomTool(
+        name="",
+        slug="",
+        method="GET",
+        url_template="https://",
+        parameters_json={"type": "object", "properties": {}, "required": []},
+        secret_placement=SECRET_NONE,
+        response_mode=RESPONSE_TEXT,
+        max_chars=8000,
+        timeout=20,
+        enabled=True,
+        public=True,
+        position=0,
+    )
+    return _detail(request, db, draft, is_new=True)
+
+
+@router.post("/admin/tools")
+async def create_tool(request: Request, db: Db, user: AdminUser) -> Response:
+    form = await request.form()
+    draft = CustomTool(headers_json={}, parameters_json={})
+    _populate(draft, form)
+    draft.position = db.scalar(select(func.coalesce(func.max(CustomTool.position), -1))) + 1
+
+    problem = _problem(db, draft, form)
+    if problem:
+        return _detail(
+            request,
+            db,
+            draft,
+            is_new=True,
+            error=problem,
+            headers_text=str(form.get("headers") or ""),
+            parameters_text=str(form.get("parameters") or ""),
+            selected_groups=set(form.getlist("group_ids")),
+        )
+
+    draft.secret_encrypted = keep_or_replace(str(form.get("secret") or ""), "")
+    draft.groups = _chosen_groups(db, form, public=draft.public)
+    db.add(draft)
+    db.commit()
+    log.info("%s added custom tool %s", user.email, draft.slug)
+    return _back(f"Added {draft.name}.")
+
+
+def _chosen_groups(db: Db, form, *, public: bool) -> list[Group]:
+    """A public tool holds no groups, the way a public model holds none."""
+    if public:
+        return []
+    ids = set(form.getlist("group_ids"))
+    return list(db.scalars(select(Group).where(Group.id.in_(ids)))) if ids else []
+
+
+@router.get("/admin/tools/{tool_id}/edit")
+async def edit_tool_page(request: Request, db: Db, user: AdminUser, tool_id: str):
+    return _detail(request, db, _tool(db, tool_id), is_new=False)
+
+
+@router.post("/admin/tools/{tool_id}/test")
+async def test_tool(request: Request, db: Db, user: AdminUser, tool_id: str):
+    """Call the stored row once, with arguments the administrator typed.
+
+    The stored row rather than the submitted form, so what is tested is what a
+    chat would actually do -- the same reason `/admin/search/test` reads the
+    saved provider settings.
+    """
+    tool = _tool(db, tool_id)
+    form = await request.form()
+    raw = str(form.get("arguments") or "").strip() or "{}"
+
+    try:
+        arguments = json.loads(raw)
+        if not isinstance(arguments, dict):
+            raise ValueError("Arguments must be a JSON object.")
+    except (json.JSONDecodeError, ValueError) as exc:
+        return render(
+            request,
+            "admin/_tool_test.html",
+            {"tool": tool, "error": f"Those arguments are not a JSON object: {exc}"},
+        )
+
+    outcome = await custom_tools.call(custom_tools.spec_from(tool), arguments)
+    tool.last_error = str(outcome.event.get("error") or "")
+    tool.last_checked_at = datetime.now(UTC)
+    db.commit()
+
+    return render(
+        request,
+        "admin/_tool_test.html",
+        {
+            "tool": tool,
+            "outcome": outcome,
+            "error": outcome.event.get("error") or "",
+            "detail": outcome.event.get("detail") or "",
+        },
+    )
+
+
+@router.post("/admin/tools/{tool_id}/delete")
+async def delete_tool(db: Db, user: AdminUser, tool_id: str) -> Response:
+    tool = _tool(db, tool_id)
+    name = tool.name
+    db.delete(tool)
+    db.commit()
+    log.info("%s deleted custom tool %s", user.email, name)
+    return _back(f"Deleted {name}.")
+
+
+@router.post("/admin/tools/{tool_id}")
+async def update_tool(request: Request, db: Db, user: AdminUser, tool_id: str) -> Response:
+    tool = _tool(db, tool_id)
+    form = await request.form()
+
+    # Validated against a draft so that a rejected save leaves the stored row
+    # untouched and the form still holds what was typed.
+    draft = CustomTool(headers_json={}, parameters_json={}, position=tool.position)
+    _populate(draft, form)
+    problem = _problem(db, draft, form, existing_id=tool.id)
+    if problem:
+        draft.id = tool.id
+        draft.secret_encrypted = tool.secret_encrypted
+        return _detail(
+            request,
+            db,
+            draft,
+            is_new=False,
+            error=problem,
+            headers_text=str(form.get("headers") or ""),
+            parameters_text=str(form.get("parameters") or ""),
+            selected_groups=set(form.getlist("group_ids")),
+        )
+
+    _populate(tool, form)
+    tool.slug = draft.slug
+    tool.parameters_json = draft.parameters_json
+    tool.secret_encrypted = keep_or_replace(str(form.get("secret") or ""), tool.secret_encrypted)
+    tool.groups = _chosen_groups(db, form, public=tool.public)
+    db.commit()
+
+    log.info("%s updated custom tool %s", user.email, tool.slug)
+    return _back(f"Saved {tool.name}.")

src/lembas/db/models/__init__.py

@@ -42,6 +42,21 @@ from lembas.db.models.library import (
 )
 from lembas.db.models.setting import Setting
 from lembas.db.models.suggestion import Suggestion
+from lembas.db.models.tool import (
+    RESPONSE_JSON,
+    RESPONSE_MODES,
+    RESPONSE_RAW,
+    RESPONSE_TEXT,
+    SECRET_BEARER,
+    SECRET_HEADER,
+    SECRET_NONE,
+    SECRET_PLACEMENTS,
+    SECRET_QUERY,
+    CustomTool,
+    McpServer,
+    custom_tool_groups,
+    mcp_server_groups,
+)
 from lembas.db.models.user import (
     ROLE_ADMIN,
     ROLE_PENDING,
@@ -63,20 +78,31 @@ __all__ = [
     "RESOURCE_BASE",
     "RESOURCE_NOTE",
     "RESOURCE_SKILL",
+    "RESPONSE_JSON",
+    "RESPONSE_MODES",
+    "RESPONSE_RAW",
+    "RESPONSE_TEXT",
     "ROLE_ADMIN",
     "ROLE_ASSISTANT",
     "ROLE_PENDING",
     "ROLE_SYSTEM",
     "ROLE_TOOL",
     "ROLE_USER",
+    "SECRET_BEARER",
+    "SECRET_HEADER",
+    "SECRET_NONE",
+    "SECRET_PLACEMENTS",
+    "SECRET_QUERY",
     "SOURCE_LINK",
     "SOURCE_UPLOAD",
     "Chat",
     "Connection",
+    "CustomTool",
     "Document",
     "Folder",
     "Group",
     "KnowledgeBase",
+    "McpServer",
     "Memory",
     "Message",
     "Model",
@@ -89,6 +115,8 @@ __all__ = [
     "Suggestion",
     "User",
     "chat_knowledge_bases",
+    "custom_tool_groups",
+    "mcp_server_groups",
     "model_groups",
     "user_groups",
 ]

src/lembas/db/models/tool.py

@@ -0,0 +1,187 @@
+"""Tools an administrator defined: HTTP endpoints and remote MCP servers.
+
+Both are instance configuration rather than someone's content, so access is
+shaped like `Model` and not like a note: a row is either public or reachable
+through the groups it names, resolved the way `permissions.models_visible_to`
+resolves a model. There is deliberately no per-user tool. A tool is a credential
+pointed at a third party, and "anyone may define one" is a different feature
+with a different threat model.
+
+The two tables are near-twins on purpose -- name, slug, secret, group list,
+last check -- because an administrator adding one should not have to learn a
+second screen. What differs is what sits between the row and the model: a
+custom tool *is* one call, described here in full, while an MCP server is a
+conversation whose tools are discovered and cached.
+"""
+
+from __future__ import annotations
+
+from datetime import datetime
+from typing import TYPE_CHECKING, Any
+
+from sqlalchemy import Boolean, Column, DateTime, ForeignKey, Integer, String, Table, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from lembas.db.base import Base, Timestamps, UUIDPrimaryKey
+from lembas.db.types import JSONDict, JSONList
+
+if TYPE_CHECKING:
+    # Annotation only; SQLAlchemy resolves the real class from its registry.
+    from lembas.db.models.user import Group
+
+# How a row's secret is attached to a request. Stored values, so these are
+# schema rather than presentation.
+SECRET_NONE = "none"
+SECRET_BEARER = "bearer"
+SECRET_HEADER = "header"
+SECRET_QUERY = "query"
+
+SECRET_PLACEMENTS = (SECRET_NONE, SECRET_BEARER, SECRET_HEADER, SECRET_QUERY)
+
+# How a response becomes text for the model.
+RESPONSE_TEXT = "text"  # prose; HTML reduced by fetch.html_to_text
+RESPONSE_JSON = "json"  # parsed, narrowed by response_path, pretty-printed
+RESPONSE_RAW = "raw"  # verbatim, truncated -- CSV, plain logs
+
+RESPONSE_MODES = (RESPONSE_TEXT, RESPONSE_JSON, RESPONSE_RAW)
+
+custom_tool_groups = Table(
+    "custom_tool_groups",
+    Base.metadata,
+    Column(
+        "tool_id", String(32), ForeignKey("custom_tools.id", ondelete="CASCADE"), primary_key=True
+    ),
+    Column("group_id", String(32), ForeignKey("groups.id", ondelete="CASCADE"), primary_key=True),
+)
+
+mcp_server_groups = Table(
+    "mcp_server_groups",
+    Base.metadata,
+    Column(
+        "server_id", String(32), ForeignKey("mcp_servers.id", ondelete="CASCADE"), primary_key=True
+    ),
+    Column("group_id", String(32), ForeignKey("groups.id", ondelete="CASCADE"), primary_key=True),
+)
+
+
+class CustomTool(UUIDPrimaryKey, Timestamps, Base):
+    """One HTTP call, described well enough for a model to decide to make it."""
+
+    __tablename__ = "custom_tools"
+
+    # `slug` IS the function name sent to the endpoint, so it is bound by the
+    # charset those accept and is fixed once the row exists: it is also half of
+    # this tool's prompt-fragment key. `name` is the human label, shown in the
+    # admin list and in the transcript.
+    slug: Mapped[str] = mapped_column(String(64), unique=True, nullable=False)
+    name: Mapped[str] = mapped_column(String(120), nullable=False)
+
+    # Sent verbatim in the tools array. The only thing the model has to decide
+    # with, which is why the form insists on it.
+    description: Mapped[str] = mapped_column(Text, default="")
+    parameters_json: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
+
+    # The *default* text of this tool's harness fragment. An administrator's
+    # edit on /admin/prompts is an override stored in the settings group like
+    # any other, so a tool deleted and recreated under the same slug keeps the
+    # wording somebody chose for it.
+    guidance: Mapped[str] = mapped_column(Text, default="")
+
+    method: Mapped[str] = mapped_column(String(8), default="GET", nullable=False)
+    # {{name}} placeholders, filled from the call's arguments. The scheme and
+    # the host must be literal -- see services/custom_tools.py for why.
+    url_template: Mapped[str] = mapped_column(String(1000), nullable=False)
+    body_template: Mapped[str] = mapped_column(Text, default="")
+    headers_json: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
+
+    secret_encrypted: Mapped[str] = mapped_column(Text, default="")
+    secret_placement: Mapped[str] = mapped_column(
+        String(16), default=SECRET_BEARER, nullable=False
+    )
+    secret_name: Mapped[str] = mapped_column(String(120), default="Authorization")
+
+    response_mode: Mapped[str] = mapped_column(String(16), default=RESPONSE_TEXT, nullable=False)
+    # A dotted path into a JSON response: "data.items.0.title". Empty is the
+    # whole document. Not JSONPath -- that is a dependency and a syntax nobody
+    # would remember for the one field they want.
+    response_path: Mapped[str] = mapped_column(String(300), default="")
+    max_chars: Mapped[int] = mapped_column(Integer, default=8000, nullable=False)
+    timeout: Mapped[int] = mapped_column(Integer, default=20, nullable=False)
+
+    # Whether this row may reach loopback, private or link-local addresses. Per
+    # row rather than the instance-wide search setting: an administrator naming
+    # http://127.0.0.1:11434 by hand is not the same act as a model handing the
+    # fetcher a URL it read on a page.
+    allow_private: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+
+    enabled: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    public: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    position: Mapped[int] = mapped_column(Integer, default=0, nullable=False)
+
+    last_checked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+    last_error: Mapped[str] = mapped_column(Text, default="")
+
+    groups: Mapped[list[Group]] = relationship(
+        "Group", secondary=custom_tool_groups, back_populates="custom_tools"
+    )
+
+    def __repr__(self) -> str:
+        return f"<CustomTool {self.slug}>"
+
+
+class McpServer(UUIDPrimaryKey, Timestamps, Base):
+    """A remote MCP server, reached over streamable HTTP.
+
+    The tools it advertises are cached in `tools_json` rather than given a table
+    of their own. A discovered tool carries exactly one administrator decision
+    -- offered or not, which `tool_overrides_json` holds -- while credentials,
+    guidance and access are all per server; and the whole list is replaced on
+    every refresh, so a table would mean reconciling rows against a cache of
+    somebody else's document.
+    """
+
+    __tablename__ = "mcp_servers"
+
+    # Prefixed onto every tool name this server advertises, so that two servers
+    # both exposing "search" do not collide and neither shadows a built-in.
+    slug: Mapped[str] = mapped_column(String(24), unique=True, nullable=False)
+    name: Mapped[str] = mapped_column(String(120), nullable=False)
+    url: Mapped[str] = mapped_column(String(1000), nullable=False)
+
+    guidance: Mapped[str] = mapped_column(Text, default="")
+
+    secret_encrypted: Mapped[str] = mapped_column(Text, default="")
+    secret_placement: Mapped[str] = mapped_column(
+        String(16), default=SECRET_BEARER, nullable=False
+    )
+    secret_name: Mapped[str] = mapped_column(String(120), default="Authorization")
+    headers_json: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
+
+    timeout: Mapped[int] = mapped_column(Integer, default=30, nullable=False)
+    max_chars: Mapped[int] = mapped_column(Integer, default=8000, nullable=False)
+    allow_private: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+
+    # The last tools/list, cached. One entry per tool:
+    # {"name", "offer_name", "description", "schema"}.
+    tools_json: Mapped[list[Any]] = mapped_column(JSONList, default=list)
+    # Per-tool switch, keyed by the server's own name for it. Absent means on,
+    # the same rule the model capability flags follow, so a newly advertised
+    # tool works rather than silently doing nothing.
+    tool_overrides_json: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
+    # What the server answered at initialize, for the admin list.
+    protocol_version: Mapped[str] = mapped_column(String(32), default="")
+    server_info: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
+
+    enabled: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    public: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    position: Mapped[int] = mapped_column(Integer, default=0, nullable=False)
+
+    last_checked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+    last_error: Mapped[str] = mapped_column(Text, default="")
+
+    groups: Mapped[list[Group]] = relationship(
+        "Group", secondary=mcp_server_groups, back_populates="mcp_servers"
+    )
+
+    def __repr__(self) -> str:
+        return f"<McpServer {self.slug}>"

src/lembas/db/models/user.py

@@ -14,6 +14,7 @@ from lembas.db.types import JSONDict
 if TYPE_CHECKING:
     # Annotation only; SQLAlchemy resolves the real class from its registry.
     from lembas.db.models.connection import Model
+    from lembas.db.models.tool import CustomTool, McpServer
 
 # Roles are a simple ordered ladder rather than a permission matrix. Groups
 # (below) carry finer-grained permissions once the users/groups UI lands.
@@ -72,6 +73,12 @@ class Group(UUIDPrimaryKey, Timestamps, Base):
     models: Mapped[list[Model]] = relationship(
         "Model", secondary="model_groups", back_populates="groups"
     )
+    custom_tools: Mapped[list[CustomTool]] = relationship(
+        "CustomTool", secondary="custom_tool_groups", back_populates="groups"
+    )
+    mcp_servers: Mapped[list[McpServer]] = relationship(
+        "McpServer", secondary="mcp_server_groups", back_populates="groups"
+    )
 
 
 class Session(UUIDPrimaryKey, Timestamps, Base):

src/lembas/main.py

@@ -19,6 +19,7 @@ from lembas.api import (
     admin_prompts,
     admin_search,
     admin_suggestions,
+    admin_tools,
     admin_users,
     audio,
     auth,
@@ -120,6 +121,7 @@ def create_app() -> FastAPI:
     app.include_router(admin_search.router)
     app.include_router(admin_prompts.router)
     app.include_router(admin_suggestions.router)
+    app.include_router(admin_tools.router)
 
     register_error_handlers(app)
     return app

src/lembas/security/permissions.py

@@ -86,6 +86,22 @@ PERMISSION_DEFS: tuple[PermissionDef, ...] = (
         True,
         "Chat",
     ),
+    PermissionDef(
+        "tools.custom",
+        "Use custom tools",
+        "Let a model call the HTTP tools an administrator has defined. Which "
+        "ones depends on the groups each tool is restricted to.",
+        True,
+        "Chat",
+    ),
+    PermissionDef(
+        "tools.mcp",
+        "Use MCP servers",
+        "Let a model call tools from the MCP servers an administrator has "
+        "added. Which ones depends on the groups each server is restricted to.",
+        True,
+        "Chat",
+    ),
     PermissionDef(
         "audio.transcribe",
         "Dictate messages",

src/lembas/services/custom_tools.py

@@ -0,0 +1,431 @@
+"""Running the HTTP tools an administrator defined.
+
+A row in `custom_tools` becomes a `ToolDef` like any built-in: same schema in
+the same array, same `ToolOutcome` back. What is different is that the arguments
+come from a model and the destination comes from a template, so two things have
+to hold.
+
+**An argument may fill a hole; it may not move the target.** The scheme and host
+of the template are literal, checked when the row is saved and again here in
+case a row predates the check, and every value is escaped for the position it
+lands in -- percent-encoded with nothing safe in a URL, JSON-escaped in a body,
+stripped of line breaks in a header. `quote(value, safe="")` is what stops a
+value adding a path segment, a query parameter or a fragment; pinning the origin
+afterwards is what catches anything that got past it.
+
+**Every hop is checked.** This is the same request-forgery problem
+`services/fetch.py` exists to solve, and the same answer: resolve and check the
+address, follow redirects by hand, refuse private ranges unless this particular
+row was allowed them. `fetch.fetch` itself cannot be reused -- it is GET-only,
+has no body, and refuses any content type that is not HTML or text, which is
+every JSON API there is -- so its redirect loop is deliberately copied rather
+than the module bent into a general HTTP client.
+
+The secret is decrypted into the snapshot and goes nowhere else: not into the
+event, not into a log line, and not across a redirect that leaves the origin it
+was issued for.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+from dataclasses import dataclass, field
+from typing import Any
+from urllib.parse import quote, urlparse
+
+import httpx
+from sqlalchemy.orm import Session as DBSession
+
+from lembas.db.models import (
+    RESPONSE_JSON,
+    RESPONSE_RAW,
+    RESPONSE_TEXT,
+    SECRET_BEARER,
+    SECRET_HEADER,
+    SECRET_QUERY,
+    CustomTool,
+    User,
+)
+from lembas.services import fetch as fetch_service
+from lembas.services import tool_access
+from lembas.services.crypto import decrypt
+from lembas.services.prompts import VARIABLE_PATTERN
+from lembas.services.tools import ToolContext, ToolDef, ToolOutcome
+
+log = logging.getLogger(__name__)
+
+# What a response may weigh before it is cut off. Well below the page fetcher's
+# ceiling, because this is text that will be sent back to a model rather than
+# stored for a person to read.
+MAX_RESPONSE_BYTES = 2 * 1024 * 1024
+
+# How much of the response is kept on the message row for the transcript. Capped
+# separately from `max_chars`: what the model reads is spent once, what the event
+# holds is stored on every message forever.
+MAX_EVENT_CHARS = 2000
+
+# How much of the arguments the transcript summarises.
+MAX_SUMMARY_CHARS = 200
+
+ALLOWED_METHODS = ("GET", "POST", "PUT", "PATCH", "DELETE")
+
+# Bounds an administrator's number is clamped into. A tool that may return
+# 400 000 characters is a tool that can fill the context window in one call.
+MIN_CHARS, MAX_CHARS = 200, 40_000
+MIN_TIMEOUT, MAX_TIMEOUT = 1, 120
+
+
+@dataclass(frozen=True)
+class HttpSpec:
+    """Everything one custom tool needs, read while the session was open.
+
+    A frozen snapshot rather than the row, for the reason `Endpoint` is one: a
+    generation outlives the request that started it, and a detached SQLAlchemy
+    instance is a trap. The decrypted secret lives here and nowhere else.
+    """
+
+    slug: str
+    label: str
+    method: str
+    url_template: str
+    body_template: str = ""
+    headers: dict[str, str] = field(default_factory=dict)
+    secret: str = ""
+    secret_placement: str = SECRET_BEARER
+    secret_name: str = "Authorization"
+    response_mode: str = RESPONSE_TEXT
+    response_path: str = ""
+    max_chars: int = 8000
+    timeout: int = 20
+    allow_private: bool = False
+    parameters: dict[str, Any] = field(default_factory=dict)
+
+    @property
+    def secret_header(self) -> str:
+        """The header the secret rides in, if it rides in one."""
+        if not self.secret or self.secret_placement not in (SECRET_BEARER, SECRET_HEADER):
+            return ""
+        return self.secret_name or "Authorization"
+
+
+def spec_from(row: CustomTool) -> HttpSpec:
+    """Snapshot a row, decrypting its secret. Call this with a session open."""
+    return HttpSpec(
+        slug=row.slug,
+        label=row.name or row.slug,
+        method=(row.method or "GET").upper(),
+        url_template=row.url_template or "",
+        body_template=row.body_template or "",
+        headers=dict(row.headers_json or {}),
+        secret=decrypt(row.secret_encrypted),
+        secret_placement=row.secret_placement,
+        secret_name=row.secret_name or "Authorization",
+        response_mode=row.response_mode,
+        response_path=row.response_path or "",
+        max_chars=min(max(int(row.max_chars or 0), MIN_CHARS), MAX_CHARS),
+        timeout=min(max(int(row.timeout or 0), MIN_TIMEOUT), MAX_TIMEOUT),
+        allow_private=bool(row.allow_private),
+        parameters=dict(row.parameters_json or {}),
+    )
+
+
+def tool_defs(
+    db: DBSession, user: User | None, *, everything: bool = False
+) -> list[ToolDef]:
+    """One `ToolDef` per custom tool this user may be offered."""
+    return [
+        ToolDef(
+            name=row.slug,
+            family=f"custom:{row.slug}",
+            description=row.description or f"Call the {row.name} tool.",
+            parameters=_schema_of(row),
+            run=_runner(spec_from(row)),
+        )
+        for row in tool_access.visible_custom_tools(db, user, everything=everything)
+    ]
+
+
+def _schema_of(row: CustomTool) -> dict[str, Any]:
+    schema = dict(row.parameters_json or {})
+    if schema.get("type") != "object":
+        # An endpoint expects an object here; anything else it will reject
+        # outright, which fails the whole request rather than the one tool.
+        return {"type": "object", "properties": {}}
+    return schema
+
+
+def _runner(spec: HttpSpec):
+    async def run(context: ToolContext, args: dict[str, Any]) -> ToolOutcome:
+        return await call(spec, args)
+
+    return run
+
+
+# --- Filling the template ----------------------------------------------------
+def _scalar(value: Any) -> str:
+    """One argument as text, before it is escaped for wherever it is going."""
+    if value is None:
+        return ""
+    if isinstance(value, bool):
+        return "true" if value else "false"
+    if isinstance(value, str):
+        return value
+    if isinstance(value, int | float):
+        return str(value)
+    return json.dumps(value, ensure_ascii=False)
+
+
+def _for_url(value: str) -> str:
+    # safe="" is the whole point: an argument must not be able to introduce a
+    # path segment, a query separator or a fragment.
+    return quote(value, safe="")
+
+
+def _for_body(value: str) -> str:
+    # The inside of a JSON string, so a quote or a backslash in an argument
+    # cannot end it early and add a field of its own.
+    return json.dumps(value, ensure_ascii=False)[1:-1]
+
+
+def _for_header(value: str) -> str:
+    # A newline in a header value is header injection. Other control characters
+    # go with it; none of them mean anything in a header.
+    return "".join(character for character in value if character.isprintable())
+
+
+def _substitute(template: str, spec: HttpSpec, args: dict[str, Any], escape) -> str:
+    """Fill `{{name}}` from the call's arguments.
+
+    Not `prompts.substitute`, though the grammar is shared. The rules differ,
+    and the differences are the point: a name the tool does not declare never
+    substitutes, an unrecognised one becomes nothing rather than passing through
+    verbatim -- a literal `{{x}}` in a URL is not a feature -- and every value
+    is escaped for where it lands.
+    """
+    declared = set(spec.parameters.get("properties") or {})
+
+    def swap(match) -> str:
+        name = match.group(1)
+        if name not in declared:
+            return ""
+        return escape(_scalar(args.get(name)))
+
+    return VARIABLE_PATTERN.sub(swap, template)
+
+
+def _origin(url: str) -> tuple[str, str]:
+    parsed = urlparse(url)
+    if parsed.scheme not in ("http", "https"):
+        raise fetch_service.FetchError("A tool's URL must start with http:// or https://")
+    if not parsed.netloc:
+        raise fetch_service.FetchError("A tool's URL has no host.")
+    return parsed.scheme, parsed.netloc
+
+
+def fill_url(spec: HttpSpec, args: dict[str, Any]) -> str:
+    """Fill the URL template, refusing anything that moved the host.
+
+    Checked twice over: the template's own scheme and authority must be literal,
+    and the filled URL must still point at them. The first check is what stops
+    `https://{{host}}/x` from ever being saved; the second is what catches a row
+    that predates it, or an escaping mistake.
+    """
+    template = spec.url_template.strip()
+    scheme, netloc = _origin(template)
+    if VARIABLE_PATTERN.search(f"{scheme}://{netloc}"):
+        raise fetch_service.FetchError(
+            "A tool's scheme and host must be literal, not filled from an argument."
+        )
+
+    filled = _substitute(template, spec, args, _for_url)
+    if _origin(filled) != (scheme, netloc):
+        raise fetch_service.FetchError("That call would have pointed somewhere else.")
+    return filled
+
+
+def _prepare(spec: HttpSpec, args: dict[str, Any]) -> tuple[str, dict[str, str], bytes | None]:
+    """The URL, headers and body for one call, secret included."""
+    url = fill_url(spec, args)
+    headers = {
+        "User-Agent": fetch_service.USER_AGENT,
+        "Accept": "application/json, text/*;q=0.9, */*;q=0.5",
+    }
+    for name, value in spec.headers.items():
+        clean = _for_header(str(name)).strip()
+        if clean:
+            headers[clean] = _substitute(str(value), spec, args, _for_header)
+
+    body: bytes | None = None
+    if spec.body_template.strip() and spec.method != "GET":
+        body = _substitute(spec.body_template, spec, args, _for_body).encode("utf-8")
+        headers.setdefault("Content-Type", "application/json")
+
+    if spec.secret:
+        if spec.secret_placement == SECRET_BEARER:
+            headers[spec.secret_name or "Authorization"] = f"Bearer {spec.secret}"
+        elif spec.secret_placement == SECRET_HEADER:
+            headers[spec.secret_name or "Authorization"] = spec.secret
+        elif spec.secret_placement == SECRET_QUERY:
+            # Only on the URL this call starts at. A redirect's Location
+            # replaces the query, so the credential does not travel on by
+            # itself -- which is the behaviour wanted anyway.
+            joiner = "&" if urlparse(url).query else "?"
+            url = f"{url}{joiner}{quote(spec.secret_name)}={quote(spec.secret, safe='')}"
+
+    return url, headers, body
+
+
+# --- Reading the response ----------------------------------------------------
+def _narrow(payload: Any, path: str) -> Any:
+    """Walk a dotted path into a decoded JSON document.
+
+    Integer segments index a list, so "data.0.title" works. A path that does not
+    lead anywhere yields the whole document rather than nothing: an unhelpful
+    answer beats a silent empty one when the model has to explain itself.
+    """
+    current = payload
+    for segment in [part for part in path.split(".") if part]:
+        if isinstance(current, dict) and segment in current:
+            current = current[segment]
+        elif isinstance(current, list) and segment.lstrip("-").isdigit():
+            try:
+                current = current[int(segment)]
+            except IndexError:
+                return payload
+        else:
+            return payload
+    return current
+
+
+def _decode(payload: bytes, response: httpx.Response) -> str:
+    return payload.decode(response.encoding or "utf-8", "replace")
+
+
+def _as_text(spec: HttpSpec, payload: bytes, response: httpx.Response) -> str:
+    content_type = response.headers.get("content-type", "")
+
+    if spec.response_mode == RESPONSE_JSON:
+        try:
+            document = json.loads(_decode(payload, response))
+        except (json.JSONDecodeError, UnicodeDecodeError):
+            # Falling back rather than failing: a JSON API answering with an
+            # HTML error page is a thing the model can report usefully.
+            return _decode(payload, response)
+        value = _narrow(document, spec.response_path)
+        if isinstance(value, str):
+            return value
+        return json.dumps(value, indent=2, ensure_ascii=False)
+
+    if spec.response_mode == RESPONSE_RAW:
+        return _decode(payload, response)
+
+    text = _decode(payload, response)
+    if "html" in content_type or text.lstrip()[:1] == "<":
+        _, text = fetch_service.html_to_text(text)
+    return text
+
+
+def _clip(text: str, limit: int) -> str:
+    if len(text) <= limit:
+        return text
+    return text[:limit].rstrip() + "\n… (truncated)"
+
+
+def _summary(args: dict[str, Any]) -> str:
+    """What the transcript shows the tool was asked for."""
+    parts = [f"{name}={_scalar(value)!r}" for name, value in args.items()]
+    return _clip(", ".join(parts), MAX_SUMMARY_CHARS)
+
+
+def _event(spec: HttpSpec, args: dict[str, Any], *, status: str, **extra: Any) -> dict[str, Any]:
+    return {
+        "name": spec.slug,
+        "kind": "custom",
+        "label": spec.label,
+        "query": _summary(args),
+        # The host, never the filled URL: a path or query segment can carry an
+        # argument, and the event is rendered and stored.
+        "detail": f"{spec.method} {urlparse(spec.url_template).netloc}",
+        "status": status,
+        "results": [],
+        **extra,
+    }
+
+
+# --- Making the call ---------------------------------------------------------
+async def call(spec: HttpSpec, args: dict[str, Any]) -> ToolOutcome:
+    """Run one custom tool. Reports its own failures rather than raising."""
+    try:
+        url, headers, body = _prepare(spec, args)
+        current = fetch_service.check_url(url, allow_private=spec.allow_private)
+        origin = _origin(current)
+        response = await _send(spec, current, headers, body, origin)
+    except fetch_service.FetchError as exc:
+        return ToolOutcome(
+            f"The {spec.label} tool could not be called: {exc.message}",
+            _event(spec, args, status="error", error=exc.message),
+        )
+    except httpx.RequestError as exc:
+        message = f"Could not reach the {spec.label} tool: {exc}"
+        return ToolOutcome(message, _event(spec, args, status="error", error=str(exc)[:200]))
+
+    payload = response.content[:MAX_RESPONSE_BYTES]
+    text = _clip(_as_text(spec, payload, response).strip(), spec.max_chars)
+
+    if response.status_code >= 400:
+        note = f"{spec.label} returned HTTP {response.status_code}."
+        return ToolOutcome(
+            f"{note}\n\n{text}" if text else note,
+            _event(
+                spec,
+                args,
+                status="error",
+                error=f"HTTP {response.status_code}",
+                text=text[:MAX_EVENT_CHARS],
+            ),
+        )
+
+    if not text:
+        return ToolOutcome(
+            f"{spec.label} returned nothing.",
+            _event(spec, args, status="ok", text=""),
+        )
+
+    return ToolOutcome(text, _event(spec, args, status="ok", text=text[:MAX_EVENT_CHARS]))
+
+
+async def _send(
+    spec: HttpSpec,
+    url: str,
+    headers: dict[str, str],
+    body: bytes | None,
+    origin: tuple[str, str],
+) -> httpx.Response:
+    """Send the request, following redirects by hand so each hop is checked."""
+    current = url
+    async with httpx.AsyncClient(timeout=spec.timeout, follow_redirects=False) as client:
+        for _ in range(fetch_service.MAX_REDIRECTS + 1):
+            response = await client.request(
+                spec.method, current, headers=headers, content=body
+            )
+            if not response.is_redirect:
+                return response
+
+            location = response.headers.get("location", "")
+            if not location:
+                raise fetch_service.FetchError("That tool redirected to nowhere.")
+            current = fetch_service.check_url(
+                str(response.url.join(location)), allow_private=spec.allow_private
+            )
+            if _origin(current) != origin:
+                # A server that can redirect us anywhere must not be able to
+                # redirect us at somebody else carrying the key.
+                if spec.secret_header:
+                    headers.pop(spec.secret_header, None)
+                origin = _origin(current)
+
+    raise fetch_service.FetchError("That tool redirected too many times.")
+
+
+__all__ = ["HttpSpec", "call", "fill_url", "spec_from", "tool_defs"]

src/lembas/services/generation.py

@@ -239,7 +239,11 @@ async def _run(generation: Generation) -> None:
             owner = db.get(User, chat.user_id)
 
             # Read while the session is open: everything below outlives it.
-            offered = tools_service.enabled_tools(db, chat, owner)
+            # Resolved once, so that what the loop is allowed to *run* is the
+            # same set the endpoint was *offered* -- not whatever happens to
+            # exist by the time a call comes back.
+            toolset = tools_service.resolve_tools(db, chat, owner)
+            offered = toolset.schemas
             payload = chat_service.build_request(
                 db, chat, upto=message, tools=offered, user=owner
             )
@@ -248,7 +252,7 @@ async def _run(generation: Generation) -> None:
             # Read here, with the rest, because titling happens after this
             # session has closed and must not open another one.
             title_prompt = prompts_service.resolve(db, "task.title")
-            tool_context = tools_service.context_for(db, owner, chat)
+            tool_context = tools_service.context_for(db, owner, chat, tools=toolset)
 
             model = chat_service.model_for(db, chat)
             generation.context_limit = model.context_length if model is not None else 0

src/lembas/services/harness.py

@@ -57,16 +57,22 @@ MAX_HARNESS_CHARS = 8000
 MAX_NAMED_DOCUMENTS = 5
 
 
-def _families(tools: list[dict[str, Any]]) -> list[str]:
+def _families(db: DBSession, tools: list[dict[str, Any]]) -> list[str]:
-    """Which families are represented in an offered tool list, in a fixed order."""
+    """Which families are represented in an offered tool list, in a fixed order.
-    from lembas.services.tools import FAMILIES, REGISTRY
 
+    Resolved against the database rather than the import-time registry, because
+    an administrator-defined tool is a row and would otherwise contribute no
+    family at all -- which is to say its guidance would never be admitted.
+    """
+    from lembas.services import tools as tools_service
+
+    book = tools_service.registry(db)
     offered = {
-        REGISTRY[name].family
+        book[name].family
         for tool in tools
-        if (name := (tool.get("function") or {}).get("name")) in REGISTRY
+        if (name := (tool.get("function") or {}).get("name")) in book
     }
-    return [family for family in FAMILIES if family in offered]
+    return [family for family in tools_service.families(db) if family in offered]
 
 
 def _tool_names(tools: list[dict[str, Any]]) -> str:
@@ -109,7 +115,7 @@ def context_variables(
     from lembas.services import tools as tools_service
 
     offered = tools or []
-    families = _families(offered)
+    families = _families(db, offered)
     stamp = datetime.now().astimezone()
 
     values: dict[str, str] = {
@@ -185,7 +191,7 @@ def compose(
     return compose_from(
         db,
         variables=context_variables(db, user, offered, chat),
-        families=_families(offered),
+        families=_families(db, offered),
         has_tools=bool(offered),
     )
 

src/lembas/services/tool_access.py

@@ -0,0 +1,63 @@
+"""Who may be offered which administrator-defined tool.
+
+One definition, used by the resolver that builds a chat's tool set and by the
+admin screens that say what a row will reach. It mirrors
+`permissions.models_visible_to` rather than `services/sharing.py`, and the
+difference matters: sharing has no admin branch because reading someone's
+private notes is not something a role should grant, while a tool is instance
+configuration an administrator could give themselves in one click anyway.
+
+`everything=True` is for callers that need to map a tool *name* back to what it
+belongs to -- the harness, the prompt preview -- rather than to decide what to
+offer. Gating on visibility there would mean an administrator's own preview
+disagreeing with what a reader actually gets.
+"""
+
+from __future__ import annotations
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session as DBSession
+
+from lembas.db.models import CustomTool, McpServer, User
+
+
+def _permitted(rows: list, user: User | None, *, everything: bool) -> list:
+    if everything or (user is not None and user.is_admin):
+        return rows
+    if user is None:
+        return []
+    member_of = {group.id for group in user.groups}
+    return [
+        row for row in rows if row.public or member_of.intersection({g.id for g in row.groups})
+    ]
+
+
+def visible_custom_tools(
+    db: DBSession, user: User | None, *, everything: bool = False
+) -> list[CustomTool]:
+    """Enabled custom tools this user may be offered, in position order."""
+    rows = list(
+        db.scalars(
+            select(CustomTool)
+            .where(CustomTool.enabled.is_(True))
+            .order_by(CustomTool.position, CustomTool.slug)
+        )
+    )
+    return _permitted(rows, user, everything=everything)
+
+
+def visible_mcp_servers(
+    db: DBSession, user: User | None, *, everything: bool = False
+) -> list[McpServer]:
+    """Enabled MCP servers this user may be offered, in position order."""
+    rows = list(
+        db.scalars(
+            select(McpServer)
+            .where(McpServer.enabled.is_(True))
+            .order_by(McpServer.position, McpServer.slug)
+        )
+    )
+    return _permitted(rows, user, everything=everything)
+
+
+__all__ = ["visible_custom_tools", "visible_mcp_servers"]

src/lembas/services/tools.py

@@ -29,10 +29,12 @@ from collections.abc import Awaitable, Callable
 from dataclasses import dataclass, field
 from typing import Any
 
+from sqlalchemy import select
 from sqlalchemy.orm import Session as DBSession
 
 from lembas.db.models import AUTHOR_MODEL, Chat, User
 from lembas.db.session import session_scope
+from lembas.services import prompts as prompts_service
 from lembas.services import search as search_service
 from lembas.services import settings_store
 from lembas.services.library import documents as documents_service
@@ -58,8 +60,24 @@ FAMILY_NOTES = "notes"
 FAMILY_MEMORY = "memory"
 FAMILY_SKILLS = "skills"
 
+# A tool that is a database row gets a family of its own, so that it can carry
+# its own guidance -- "custom:weather", "mcp:github". Everything before the
+# colon is the *gate*: the capability flag and the permission are per gate, not
+# per row, because a server advertising forty tools must not mean forty
+# checkboxes on every model.
+FAMILY_CUSTOM = "custom"
+FAMILY_MCP = "mcp"
+
+# The built-in families, in the order they are offered.
 FAMILIES = (FAMILY_SEARCH, FAMILY_KNOWLEDGE, FAMILY_NOTES, FAMILY_MEMORY, FAMILY_SKILLS)
 
+GATES = (*FAMILIES, FAMILY_CUSTOM, FAMILY_MCP)
+
+
+def gate_of(family: str) -> str:
+    """The part a capability flag and a permission are named after."""
+    return family.split(":", 1)[0]
+
 
 @dataclass
 class ToolContext:
@@ -72,10 +90,14 @@ class ToolContext:
 
     owner_id: str
     search_config: dict[str, Any] = field(default_factory=dict)
-    allow_private_fetch: bool = False
     # Which knowledge bases this chat is scoped to. Empty means "everything the
     # owner can see", which is what a chat with none attached should do.
     base_ids: list[str] = field(default_factory=list)
+    # Name -> definition for the tools actually offered on this request. None
+    # means nobody resolved a set, and only then does `run_tool` fall back to
+    # the import-time registry. A dict, *even an empty one*, is authoritative:
+    # a model naming a tool it was not offered must not get it run.
+    tools: dict[str, ToolDef] | None = None
 
 
 @dataclass
@@ -114,6 +136,31 @@ class ToolDef:
         }
 
 
+@dataclass(frozen=True)
+class ToolSet:
+    """What one request may call: the schemas to send, and how to run them.
+
+    The two halves have to travel together. `enabled_tools` used to return
+    schemas alone, which worked only because every runner was reachable through
+    the import-time `REGISTRY`. A tool that is a database row is not, so the
+    resolution has to be carried from the session that made it to the loop that
+    uses it.
+    """
+
+    defs: tuple[ToolDef, ...] = ()
+
+    @property
+    def schemas(self) -> list[dict[str, Any]]:
+        return [tool.schema for tool in self.defs]
+
+    @property
+    def by_name(self) -> dict[str, ToolDef]:
+        return {tool.name: tool for tool in self.defs}
+
+    def __bool__(self) -> bool:
+        return bool(self.defs)
+
+
 def _object(properties: dict[str, Any], required: list[str]) -> dict[str, Any]:
     return {"type": "object", "properties": properties, "required": required}
 
@@ -645,21 +692,69 @@ def _family_allowed(
     Absent counts as on when `tools` is on, so an upgrade does not silently take
     web search away from every model already set up for it.
     """
+    gate = gate_of(family)
     default = bool(capabilities.get("tools"))
-    if not capabilities.get(f"tool_{family}", default):
+    if not capabilities.get(f"tool_{gate}", default):
         return False
 
-    if family == FAMILY_SEARCH:
+    if gate == FAMILY_SEARCH:
         return bool(
             allowed.get("tools.web_search")
             and config.get("enabled")
             and not search_service.availability(str(config.get("provider") or "ddgs"))
         )
-    return bool(allowed.get(f"tools.{family}") and allowed.get("library.use"))
+    if gate in (FAMILY_CUSTOM, FAMILY_MCP):
+        # Deliberately without `library.use`: an HTTP endpoint an administrator
+        # wrote has nothing to do with this person's own documents and notes,
+        # and requiring the library permission for it would be a coincidence of
+        # naming rather than a rule.
+        return bool(allowed.get(f"tools.{gate}"))
+    return bool(allowed.get(f"tools.{gate}") and allowed.get("library.use"))
 
 
-def enabled_tools(db: DBSession, chat: Chat, user: User | None) -> list[dict[str, Any]]:
+def _row_defs(db: DBSession, user: User | None, *, everything: bool = False) -> list[ToolDef]:
-    """The tool schemas to offer for this chat."""
+    """Tool definitions built from rows, in the order they claim names.
+
+    Imported here rather than at the top because `custom_tools` needs `ToolDef`
+    from this module.
+    """
+    from lembas.services import custom_tools
+
+    return custom_tools.tool_defs(db, user, everything=everything)
+
+
+def _book(defs: list[ToolDef]) -> dict[str, ToolDef]:
+    """Keyed by name, first claim winning.
+
+    The built-ins are laid down first, so a row can never shadow one -- a tool
+    called `notes_delete` that turns out to be somebody's HTTP endpoint is the
+    kind of surprise that has no good failure mode.
+    """
+    book = dict(REGISTRY)
+    for tool in defs:
+        book.setdefault(tool.name, tool)
+    return book
+
+
+def registry(db: DBSession) -> dict[str, ToolDef]:
+    """Every tool that exists on this instance, keyed by name, ungated.
+
+    `REGISTRY` holds the built-ins alone, because it is built at import time and
+    an administrator-defined tool is a row. Callers that only need to map a name
+    back to a family use this; callers deciding what to *offer* use
+    `resolve_tools`, which applies the gates as well.
+    """
+    return _book(_row_defs(db, None, everything=True))
+
+
+def families(db: DBSession) -> tuple[str, ...]:
+    """Every family that exists, the built-ins in their fixed order first."""
+    rows = tuple(tool.family for tool in _row_defs(db, None, everything=True))
+    return (*FAMILIES, *rows)
+
+
+def resolve_tools(db: DBSession, chat: Chat, user: User | None) -> ToolSet:
+    """Every tool this chat may call right now, with its runner attached."""
     from lembas.security import permissions
     from lembas.services import chat as chat_service
 
@@ -669,25 +764,47 @@ def enabled_tools(db: DBSession, chat: Chat, user: User | None) -> list[dict[str
         capabilities = model.capabilities_json or {}
 
     if not capabilities.get("tools"):
-        return []
+        return ToolSet()
 
     allowed = permissions.resolve(db, user)
     config = settings_store.search(db)
 
-    families = {
+    # Resolved against what this reader may see, not against everything that
-        family
+    # exists: a tool restricted to a group is not offered outside it.
-        for family in FAMILIES
+    book = _book(_row_defs(db, user))
-        if _family_allowed(family, config=config, capabilities=capabilities, allowed=allowed)
+    return ToolSet(
-    }
+        tuple(
-    return [tool.schema for tool in REGISTRY.values() if tool.family in families]
+            tool
+            for tool in book.values()
+            if _family_allowed(
+                tool.family, config=config, capabilities=capabilities, allowed=allowed
+            )
+        )
+    )
 
 
-def context_for(db: DBSession, user: User | None, chat: Chat | None = None) -> ToolContext:
+def enabled_tools(db: DBSession, chat: Chat, user: User | None) -> list[dict[str, Any]]:
+    """The tool schemas to offer for this chat.
+
+    The shape is unchanged on purpose: the inspector and `build_request` want
+    exactly this. Anything that will also *run* a tool wants `resolve_tools`.
+    """
+    return resolve_tools(db, chat, user).schemas
+
+
+def context_for(
+    db: DBSession,
+    user: User | None,
+    chat: Chat | None = None,
+    *,
+    tools: ToolSet | None = None,
+) -> ToolContext:
     """The snapshot a running tool needs, taken while the session is open."""
     return ToolContext(
         owner_id=user.id if user else "",
         search_config=settings_store.search(db),
         base_ids=[base.id for base in chat.knowledge_bases] if chat is not None else [],
+        tools=tools.by_name if tools is not None else None,
     )
 
 
@@ -697,8 +814,15 @@ async def run_tool(context: ToolContext, name: str, arguments: str) -> ToolOutco
     Never raises. A tool that fails hands the model an explanation and lets it
     carry on -- a failed lookup should produce "I could not find that" rather
     than killing the whole reply.
+
+    The lookup is against what was *offered*, not against everything that
+    exists. Reaching for the registry directly meant a model naming a tool its
+    chat was gated out of -- a family switched off for the model, a permission
+    the reader does not have -- had it run anyway, because only the offer was
+    ever filtered.
     """
-    tool = REGISTRY.get(name)
+    book = REGISTRY if context.tools is None else context.tools
+    tool = book.get(name)
     if tool is None:
         return ToolOutcome(
             f"There is no tool called {name!r}.",
@@ -710,9 +834,12 @@ async def run_tool(context: ToolContext, name: str, arguments: str) -> ToolOutco
     except json.JSONDecodeError:
         # Small models emit malformed argument JSON often enough that this is a
         # normal path, not an exceptional one. Treat the whole string as the
-        # first required argument rather than giving up.
+        # tool's first argument rather than giving up: what it says is required,
-        required = tool.parameters.get("required") or ["query"]
+        # else the first thing it declares, and only then a guess -- a schema
-        parsed = {required[0]: arguments.strip()}
+        # somebody else wrote need not have either.
+        properties = tool.parameters.get("properties") or {}
+        names = tool.parameters.get("required") or list(properties) or ["query"]
+        parsed = {str(names[0]): arguments.strip()}
     if not isinstance(parsed, dict):
         parsed = {"query": str(parsed)}
 
@@ -808,6 +935,31 @@ def tool_turn(call: dict[str, Any], content: str) -> dict[str, Any]:
     }
 
 
+def _row_source(db: DBSession):
+    """One harness fragment per administrator-defined tool.
+
+    The seam `prompts.register_source` exists for. The row supplies the default
+    text and the admin page supplies the override, which is why a tool deleted
+    and recreated under the same slug keeps whatever wording somebody chose for
+    it -- the override outlives the row.
+
+    Gated on the tool's own family, so the guidance appears exactly when the
+    tool it describes is offered and never otherwise.
+    """
+    from lembas.db.models import CustomTool
+
+    for row in db.scalars(select(CustomTool).order_by(CustomTool.position, CustomTool.slug)):
+        yield prompts_service.Fragment(
+            key=f"tool.custom_{row.slug}",
+            label=row.name or row.slug,
+            group=prompts_service.GROUP_TOOLS,
+            order=500 + row.position,
+            families=(f"{FAMILY_CUSTOM}:{row.slug}",),
+            hint=f"Appears when the {row.slug} tool is offered.",
+            default=row.guidance or "",
+        )
+
+
 __all__ = [
     "FAMILIES",
     "MAX_ROUNDS",
@@ -816,9 +968,19 @@ __all__ = [
     "ToolContext",
     "ToolDef",
     "ToolOutcome",
+    "ToolSet",
     "assistant_turn",
     "context_for",
     "enabled_tools",
+    "families",
+    "registry",
+    "resolve_tools",
     "run_tool",
     "tool_turn",
 ]
+
+
+# Registered at import. `services.tools` is imported by the chat routes, the
+# generation service and the prompts admin, so the source is in place before
+# anything renders a catalogue.
+prompts_service.register_source(_row_source)

src/lembas/web/static/css/chat.css

@@ -371,6 +371,23 @@
   line-height: var(--leading-relaxed);
 }
 
+/* What a tool returned, verbatim. Preformatted rather than rendered: this is
+   third-party text and markdown is the one path allowed to emit HTML. */
+.tool-result__text {
+  margin: 0;
+  padding: var(--sp-3);
+  border-radius: var(--radius-sm);
+  background: var(--bg-sunken);
+  color: var(--ink-muted);
+  font-family: var(--font-mono);
+  font-size: var(--text-xs);
+  line-height: var(--leading-relaxed);
+  white-space: pre-wrap;
+  overflow-wrap: anywhere;
+  max-height: 22em;
+  overflow-y: auto;
+}
+
 /* --- Stop, notes and editing ---------------------------------------------- */
 .msg__status { font-size: var(--text-xs); color: var(--ink-faint); font-style: italic; }
 .msg__status:empty { display: none; }

src/lembas/web/templates/admin/_layout.html

@@ -43,6 +43,10 @@
           {{ icon("globe", "icon--sm") }}
           <span class="nav-item__label">Web search</span>
         </a>
+        <a class="nav-item {{ 'is-active' if section == 'tools' }}" href="/admin/tools">
+          {{ icon("link", "icon--sm") }}
+          <span class="nav-item__label">Tools</span>
+        </a>
         <a class="nav-item {{ 'is-active' if section == 'prompts' }}" href="/admin/prompts">
           {{ icon("sparkle", "icon--sm") }}
           <span class="nav-item__label">Prompts</span>
@@ -64,10 +68,6 @@
 
       <div class="nav-group">
         <div class="nav-group__label">Not yet built</div>
-        <span class="nav-item is-disabled">
-          {{ icon("gear", "icon--sm") }}
-          <span class="nav-item__label">Tools</span>
-        </span>
         <span class="nav-item is-disabled">
           {{ icon("server", "icon--sm") }}
           <span class="nav-item__label">Agents</span>

src/lembas/web/templates/admin/_tool_test.html

@@ -0,0 +1,21 @@
+{% from "_macros.html" import icon %}
+{#
+  The result of calling one tool by hand.
+
+  What comes back is whatever the endpoint chose to send, which makes it exactly
+  as untrusted as a search result or model output. It is shown escaped, inside a
+  <pre>, and never rendered as Markdown.
+#}
+{% if error %}
+<div class="alert alert--error">{{ icon("warning", "icon--sm") }} <span>{{ error }}</span></div>
+{% else %}
+<div class="alert alert--success">
+  {{ icon("check", "icon--sm") }}
+  <span>{{ detail or tool.slug }} answered.</span>
+</div>
+{% endif %}
+
+{% if outcome %}
+<p class="field__hint">This is what the model would read back:</p>
+<pre class="tool-result__text">{{ outcome.content }}</pre>
+{% endif %}

src/lembas/web/templates/admin/tool_detail.html

@@ -0,0 +1,308 @@
+{% extends "admin/_layout.html" %}
+{% from "_macros.html" import icon %}
+{% set section = "tools" %}
+
+{% block title %}{{ "New tool" if is_new else tool.name }} - LLeMbas{% endblock %}
+{% block heading %}{{ "New tool" if is_new else tool.name }}{% endblock %}
+
+{% block admin_content %}
+<nav class="crumbs">
+  <a class="crumbs__back" href="/admin/tools">
+    {{ icon("chevron-right", "icon--sm crumbs__icon") }} All tools
+  </a>
+</nav>
+
+{% if error %}
+<div class="alert alert--error">{{ icon("warning", "icon--sm") }} <span>{{ error }}</span></div>
+{% endif %}
+
+<form method="post" action="{{ '/admin/tools' if is_new else '/admin/tools/' ~ tool.id }}"
+      class="form-grid">
+
+  <section class="card">
+    <h2 class="card__title">What it is</h2>
+
+    <div class="field">
+      <label class="field__label" for="name">Name</label>
+      <input class="input" id="name" name="name" value="{{ tool.name }}" required
+             maxlength="120" placeholder="Weather">
+      <p class="field__hint">Shown in the transcript when the model uses it.</p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="slug">Identifier</label>
+      <input class="input input--mono" id="slug" name="slug" value="{{ tool.slug }}" required
+             maxlength="48" placeholder="weather" pattern="[a-z0-9][a-z0-9_\-]*">
+      <p class="field__hint">
+        The name the model calls, and the key its guidance is stored under.
+        Lowercase letters, digits, hyphens and underscores.
+        {% if not is_new %}Changing it starts its guidance afresh.{% endif %}
+      </p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="description">Description</label>
+      <textarea class="textarea" id="description" name="description" rows="3"
+                placeholder="Look up the current weather for a city."
+                >{{ tool.description }}</textarea>
+      <p class="field__hint">
+        Sent to the model verbatim. This is the whole basis on which it decides
+        whether to call this tool, so say what it does and when it is the right
+        thing to use.
+      </p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="parameters">Parameters</label>
+      <textarea class="textarea input--mono" id="parameters" name="parameters" rows="10"
+                spellcheck="false">{{ parameters_text }}</textarea>
+      <p class="field__hint">
+        A JSON Schema object. Each property becomes a
+        <code>{{ '{{name}}' }}</code> you can use below, and a
+        <code>description</code> on each one is worth writing — the model reads
+        those too.
+      </p>
+    </div>
+  </section>
+
+  <section class="card">
+    <h2 class="card__title">The call</h2>
+
+    <div class="field">
+      <label class="field__label" for="method">Method</label>
+      <select class="select" id="method" name="method">
+        {% for method in methods %}
+        <option value="{{ method }}" {{ 'selected' if method == tool.method }}>{{ method }}</option>
+        {% endfor %}
+      </select>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="url_template">URL</label>
+      <input class="input input--mono" id="url_template" name="url_template" required
+             value="{{ tool.url_template }}"
+             placeholder="https://api.example.com/weather/{{ '{{city}}' }}">
+      <p class="field__hint">
+        Placeholders are filled from the arguments and escaped, so a value
+        cannot add a path segment or a query of its own. The scheme and host
+        must be written out — they cannot come from an argument.
+      </p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="headers">Headers</label>
+      <textarea class="textarea input--mono" id="headers" name="headers" rows="3"
+                spellcheck="false"
+                placeholder="Accept: application/json">{{ headers_text }}</textarea>
+      <p class="field__hint">One <code>Name: value</code> per line. Placeholders work here too.</p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="body_template">Body</label>
+      <textarea class="textarea input--mono" id="body_template" name="body_template" rows="4"
+                spellcheck="false">{{ tool.body_template }}</textarea>
+      <p class="field__hint">
+        Ignored for GET. Placeholders are escaped for JSON, so a value cannot
+        end the string it sits in and add a field.
+      </p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="timeout">Timeout (seconds)</label>
+      <input class="input" id="timeout" name="timeout" value="{{ tool.timeout }}" inputmode="numeric">
+    </div>
+  </section>
+
+  <section class="card">
+    <h2 class="card__title">Credential</h2>
+
+    <div class="field">
+      <label class="field__label" for="secret_placement">How it is sent</label>
+      <select class="select" id="secret_placement" name="secret_placement">
+        {% for value, label in secret_placements %}
+        <option value="{{ value }}" {{ 'selected' if value == tool.secret_placement }}>
+          {{ label }}
+        </option>
+        {% endfor %}
+      </select>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="secret_name">Header or parameter name</label>
+      <input class="input input--mono" id="secret_name" name="secret_name"
+             value="{{ tool.secret_name }}" maxlength="120">
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="secret">Secret</label>
+      <input class="input input--mono" id="secret" name="secret" type="password"
+             autocomplete="off" placeholder="No secret set"
+             value="{{ unchanged if tool.secret_encrypted else '' }}">
+      <p class="field__hint">
+        {% if tool.secret_encrypted %}
+          Currently <code>{{ masked }}</code>. Leave the dots alone to keep it,
+          or clear the field to remove it.
+        {% else %}
+          Encrypted at rest and never shown again. It is dropped if the endpoint
+          redirects to another host.
+        {% endif %}
+      </p>
+    </div>
+  </section>
+
+  <section class="card">
+    <h2 class="card__title">The answer</h2>
+
+    <div class="field">
+      <label class="field__label" for="response_mode">Read the response as</label>
+      <select class="select" id="response_mode" name="response_mode">
+        {% for value, label in response_modes %}
+        <option value="{{ value }}" {{ 'selected' if value == tool.response_mode }}>{{ label }}</option>
+        {% endfor %}
+      </select>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="response_path">Path into the JSON</label>
+      <input class="input input--mono" id="response_path" name="response_path"
+             value="{{ tool.response_path }}" placeholder="data.items.0.title" maxlength="300">
+      <p class="field__hint">
+        Dotted; a number indexes a list. Leave empty for the whole document.
+        A path that leads nowhere gives the whole document rather than nothing.
+      </p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="max_chars">Most characters to keep</label>
+      <input class="input" id="max_chars" name="max_chars" value="{{ tool.max_chars }}"
+             inputmode="numeric">
+      <p class="field__hint">
+        Spent out of the context window on every call. The rest is cut off, and
+        the model is told so.
+      </p>
+    </div>
+  </section>
+
+  <section class="card">
+    <h2 class="card__title">Guidance</h2>
+
+    <div class="field">
+      <textarea class="textarea" name="guidance" rows="4"
+                placeholder="- Check the weather rather than guessing at it."
+                >{{ tool.guidance }}</textarea>
+      <p class="field__hint">
+        Added to the system message whenever this tool is offered, and nowhere
+        else. Start a line with <code>- </code> and it joins the list of tool
+        instructions. Optional: the description above is what makes the tool
+        usable, this is for habits.
+        {% if prompt_overridden %}
+          <br><strong>Someone has overridden this wording under
+          <a href="/admin/prompts">Prompts</a></strong> — that is what the model
+          sees, not this.
+        {% endif %}
+      </p>
+    </div>
+  </section>
+
+  <section class="card">
+    <h2 class="card__title">Availability</h2>
+
+    <div class="field">
+      <div class="checkbox-row">
+        <label class="checkbox">
+          <input type="checkbox" name="enabled" value="true" {{ 'checked' if tool.enabled }}>
+          <span>Enabled — offered in chats</span>
+        </label>
+        <label class="checkbox">
+          <input type="checkbox" name="allow_private" value="true"
+                 {{ 'checked' if tool.allow_private }}>
+          <span>May reach private and loopback addresses</span>
+        </label>
+      </div>
+      <p class="field__hint">
+        Leave the second unticked unless this tool points at something on your
+        own network. It is what stops a tool being aimed at this server, a
+        router, or a cloud metadata endpoint.
+      </p>
+    </div>
+
+    <div class="field">
+      <label class="checkbox">
+        <input type="checkbox" name="public" value="true" {{ 'checked' if tool.public }}>
+        <span>Available to everyone</span>
+      </label>
+      <p class="field__hint">
+        Uncheck to restrict this tool to chosen groups. Administrators always
+        have access.
+      </p>
+    </div>
+
+    <div class="field">
+      <span class="field__label">Groups with access</span>
+      {% if groups %}
+      <div class="checkbox-row">
+        {% for group in groups %}
+        <label class="checkbox">
+          <input type="checkbox" name="group_ids" value="{{ group.id }}"
+                 {{ 'checked' if group.id in selected_groups }}>
+          <span>{{ group.name }}</span>
+        </label>
+        {% endfor %}
+      </div>
+      <p class="field__hint">Ignored while the tool is available to everyone.</p>
+      {% else %}
+      <p class="field__hint">
+        No groups yet — <a href="/admin/groups">create one</a> to restrict access.
+      </p>
+      {% endif %}
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="position">Position</label>
+      <input class="input" id="position" name="position" value="{{ tool.position }}"
+             inputmode="numeric">
+    </div>
+  </section>
+
+  <div class="btn-row">
+    <button class="btn btn--primary" type="submit">
+      {{ "Create tool" if is_new else "Save changes" }}
+    </button>
+    <a class="btn btn--ghost" href="/admin/tools">Back to all tools</a>
+    {% if not is_new %}
+    <button class="btn btn--danger" type="submit" formnovalidate
+            formaction="/admin/tools/{{ tool.id }}/delete"
+            data-confirm-button="Delete the tool “{{ tool.name }}”? Chats that used it keep their transcripts.">
+      Delete
+    </button>
+    {% endif %}
+  </div>
+</form>
+
+{% if not is_new %}
+<section class="card">
+  <h2 class="card__title">Try it</h2>
+  <p class="field__hint">
+    Calls the <em>saved</em> tool once, so what you see here is what a chat would
+    get. Nothing is sent to a model.
+  </p>
+
+  <div class="field">
+    <label class="field__label" for="arguments">Arguments</label>
+    <textarea class="textarea input--mono" id="arguments" name="arguments" rows="3"
+              spellcheck="false">{"city": "Minas Tirith"}</textarea>
+  </div>
+
+  <div class="btn-row">
+    <button class="btn" type="button"
+            hx-post="/admin/tools/{{ tool.id }}/test"
+            hx-include="#arguments"
+            hx-target="#tool-test-result">
+      {{ icon("refresh", "icon--sm") }} Run once
+    </button>
+  </div>
+
+  <div id="tool-test-result"></div>
+</section>
+{% endif %}
+{% endblock %}

src/lembas/web/templates/admin/tools.html

@@ -0,0 +1,110 @@
+{% extends "admin/_layout.html" %}
+{% from "_macros.html" import icon %}
+{% set section = "tools" %}
+
+{% block title %}Tools - LLeMbas{% endblock %}
+{% block heading %}Tools{% endblock %}
+
+{% block admin_content %}
+<p class="admin-lede">
+  HTTP calls a model can make while it answers. Each one is offered to models
+  marked <strong>Custom tools</strong>, to people who have the permission, and —
+  if it is restricted — only to the groups you choose. The model decides
+  <em>when</em> to call it from the description you write, so write that as if
+  explaining to a colleague what the tool is for.
+</p>
+
+{% if saved %}
+<div class="alert alert--success">{{ icon("check", "icon--sm") }} <span>{{ saved }}</span></div>
+{% endif %}
+
+{% if not total %}
+<div class="empty" style="padding: var(--sp-10) 0">
+  {{ icon("link", "empty__mark") }}
+  <p class="empty__text">
+    No tools yet. <a href="/admin/tools/new">Define one</a> — a name, a
+    description, and a URL with <code>{{ '{{placeholders}}' }}</code> in it.
+  </p>
+</div>
+{% else %}
+
+{# Filters are links, so a filtered view is a real URL you can keep or share. #}
+<div class="filter-bar">
+  <div class="filter-tabs">
+    {% for key, label in filters.items() %}
+    <a class="filter-tab {{ 'is-active' if key == active_filter }}"
+       href="/admin/tools?filter={{ key }}{% if q %}&q={{ q|urlencode }}{% endif %}">
+      {{ label }} <span class="filter-tab__count">{{ counts[key] }}</span>
+    </a>
+    {% endfor %}
+  </div>
+
+  <form class="filter-form" method="get" action="/admin/tools">
+    <input type="hidden" name="filter" value="{{ active_filter }}">
+    <input class="input" type="search" name="q" value="{{ q }}"
+           placeholder="Search tools…" aria-label="Search tools">
+    <button class="btn" type="submit">{{ icon("search", "icon--sm") }} Filter</button>
+    {% if q or active_filter != "all" %}
+    <a class="btn btn--ghost" href="/admin/tools">Clear</a>
+    {% endif %}
+    <a class="btn btn--primary" href="/admin/tools/new">{{ icon("plus", "icon--sm") }} New tool</a>
+  </form>
+</div>
+
+{% if not tools %}
+<div class="empty" style="padding: var(--sp-8) 0">
+  <p class="empty__text">Nothing matches that filter.</p>
+</div>
+{% else %}
+
+<div class="model-rows">
+  {% for tool in tools %}
+  <div class="model-row {{ 'is-off' if not tool.enabled }}">
+    <span class="model-row__pos">{{ page_start + loop.index }}</span>
+
+    <div class="model-row__main">
+      <div class="model-row__title">
+        <a class="model-row__name" href="/admin/tools/{{ tool.id }}/edit">{{ tool.name }}</a>
+        {% if not tool.enabled %}<span class="badge badge--danger">disabled</span>{% endif %}
+        {% if not tool.public %}<span class="badge">restricted</span>{% endif %}
+        {% if tool.allow_private %}<span class="badge">private network</span>{% endif %}
+        {% if tool.last_error %}<span class="badge badge--danger">last call failed</span>{% endif %}
+      </div>
+      <code class="model-row__id">
+        {{ tool.slug }} · {{ tool.method }} {{ tool.url_template }}
+      </code>
+    </div>
+
+    <div class="model-row__actions">
+      <a class="btn btn--sm" href="/admin/tools/{{ tool.id }}/edit">Edit</a>
+    </div>
+  </div>
+  {% endfor %}
+</div>
+
+<div class="list-footer">
+  <span class="text-xs faint">
+    Showing {{ page_start + 1 }}–{{ page_start + tools|length }} of {{ matched }}
+    {%- if matched != total %} (filtered from {{ total }}){% endif %}
+  </span>
+
+  {% if pages > 1 %}
+  {% set base = "/admin/tools?filter=" ~ active_filter ~ ("&q=" ~ q|urlencode if q else "") %}
+  <div class="btn-row">
+    {% if page > 1 %}
+    <a class="btn btn--sm" href="{{ base }}&page={{ page - 1 }}">Previous</a>
+    {% else %}
+    <span class="btn btn--sm" aria-disabled="true" style="opacity: .45">Previous</span>
+    {% endif %}
+    <span class="text-xs faint">Page {{ page }} of {{ pages }}</span>
+    {% if page < pages %}
+    <a class="btn btn--sm" href="{{ base }}&page={{ page + 1 }}">Next</a>
+    {% else %}
+    <span class="btn btn--sm" aria-disabled="true" style="opacity: .45">Next</span>
+    {% endif %}
+  </div>
+  {% endif %}
+</div>
+{% endif %}
+{% endif %}
+{% endblock %}

src/lembas/web/templates/chat/_tool_activity.html

@@ -6,16 +6,36 @@
   answer) and from the stored message afterwards, so the sources behind an
   answer stay in the transcript rather than vanishing when the stream ends.
 
-  EVERYTHING in here comes from a search provider and is untrusted, exactly as
+  EVERYTHING in here is third-party text and is untrusted, exactly as much as
-  much as model output is. Jinja autoescaping covers the text; the URL is
+  model output is -- a search provider's results, an administrator's HTTP tool
-  checked separately, because `is_linkable` is the only thing standing between
+  relaying whatever it was pointed at, an MCP server's reply. Jinja autoescaping
-  a result carrying a javascript: URL and an anchor pointing at it.
+  covers it. Two things are handled separately: the URL, because `is_linkable`
+  is the only thing standing between a result carrying a javascript: URL and an
+  anchor pointing at it, and `event.text`, which is rendered as preformatted
+  text and deliberately NOT through services/markdown.py -- markdown is the one
+  path allowed to emit HTML, and this is the last content that should be given
+  it.
+
+  `kind` says how to label the event. Rows written before it existed have none,
+  so web_search reads as a search and everything else falls to the generic
+  branch: an old notes_search event used to claim it had searched the web.
 #}
 {% for event in tool_events %}
+{% set kind = event.kind or ('search' if event.name == 'web_search' else 'tool') %}
 <details class="tool-activity {{ 'tool-activity--error' if event.status == 'error' }}">
   <summary class="tool-activity__summary">
+    {% if kind == 'search' %}
       {{ icon("globe", "icon--sm tool-activity__icon") }}
+    {% elif kind == 'custom' %}
+      {{ icon("link", "icon--sm tool-activity__icon") }}
+    {% elif kind == 'mcp' %}
+      {{ icon("server", "icon--sm tool-activity__icon") }}
+    {% else %}
+      {{ icon("sparkle", "icon--sm tool-activity__icon") }}
+    {% endif %}
+
     <span class="tool-activity__label">
+      {% if kind == 'search' %}
         {% if event.status == "error" %}
           Web search failed
         {% elif event.query %}
@@ -23,6 +43,18 @@
         {% else %}
           Searched the web
         {% endif %}
+      {% else %}
+        {% set label = event.label or event.name %}
+        {% if event.status == "error" %}
+          {{ label }} failed
+        {% else %}
+          {{ label }}
+        {% endif %}
+        {% if event.query %}
+          <span class="tool-activity__count">· {{ event.query }}</span>
+        {% endif %}
+      {% endif %}
+
       {% if event.results %}
         <span class="tool-activity__count">
           · {{ event.results | length }} result{{ '' if event.results | length == 1 else 's' }}
@@ -33,21 +65,29 @@
   </summary>
 
   <div class="tool-activity__body">
+    {% if event.detail and kind != 'search' %}
+    <p class="tool-result__host">{{ event.detail }}</p>
+    {% endif %}
+
     {% if event.error %}
     <p class="tool-activity__error">{{ event.error }}</p>
-    {% elif not event.results %}
+    {% elif not event.results and not event.text %}
     <p class="tool-activity__error">Nothing was found.</p>
     {% endif %}
 
+    {% if event.text %}
+    <pre class="tool-result__text">{{ event.text }}</pre>
+    {% endif %}
+
     {% for result in event.results %}
     <div class="tool-result">
-      {% set scheme = result.url.split(":")[0] | lower %}
+      {% set scheme = (result.url or "").split(":")[0] | lower %}
       {% if scheme in ("http", "https") %}
       <a class="tool-result__title" href="{{ result.url }}"
          target="_blank" rel="noopener noreferrer nofollow">{{ result.title }}</a>
       {% else %}
-      {# Not a link. A search result is third-party text and its URL is not
+      {# Not a link. A result is third-party text and its URL is not trusted to
-         trusted to be safe to click. #}
+         be safe to click. #}
       <span class="tool-result__title">{{ result.title }}</span>
       {% endif %}
       <span class="tool-result__host">{{ result.host }}</span>

tests/test_admin_tools.py

@@ -0,0 +1,303 @@
+"""The custom-tools admin screen."""
+
+from __future__ import annotations
+
+import json
+
+import httpx
+import pytest
+from fastapi.testclient import TestClient
+from sqlalchemy import select
+
+from lembas.db.models import CustomTool, Group, User
+from lembas.security.passwords import hash_password
+from lembas.services.crypto import UNCHANGED_SENTINEL, decrypt, encrypt
+
+
+@pytest.fixture
+def plain_user(client: TestClient, db, registered):
+    """A second account, which is never an administrator."""
+    client.post("/auth/logout")
+    client.post(
+        "/auth/register",
+        data={"name": "Sam", "email": "sam@shire.test", "password": "correct horse battery"},
+        follow_redirects=False,
+    )
+    user = db.scalar(select(User).where(User.email == "sam@shire.test"))
+    user.role = "user"
+    user.active = True
+    db.commit()
+    client.post(
+        "/auth/login",
+        data={"email": "sam@shire.test", "password": "correct horse battery"},
+        follow_redirects=False,
+    )
+    return user
+
+
+def _form(**overrides) -> dict:
+    base = {
+        "name": "Weather",
+        "slug": "weather",
+        "description": "Look up the weather for a city.",
+        "parameters": json.dumps(
+            {"type": "object", "properties": {"city": {"type": "string"}}, "required": ["city"]}
+        ),
+        "method": "GET",
+        "url_template": "https://api.test/v1/{{city}}",
+        "headers": "Accept: application/json",
+        "secret_placement": "bearer",
+        "secret_name": "Authorization",
+        "response_mode": "json",
+        "max_chars": "8000",
+        "timeout": "20",
+        "position": "0",
+        "enabled": "true",
+        "public": "true",
+    }
+    base.update(overrides)
+    return {key: value for key, value in base.items() if value is not None}
+
+
+def _create(client: TestClient, **overrides):
+    return client.post("/admin/tools", data=_form(**overrides), follow_redirects=False)
+
+
+# --- Guards ------------------------------------------------------------------
+def test_the_pages_are_refused_to_a_plain_user(client: TestClient, plain_user):
+    assert client.get("/admin/tools").status_code == 403
+    assert client.get("/admin/tools/new").status_code == 403
+    assert client.post("/admin/tools", data=_form()).status_code == 403
+
+
+def test_a_tool_that_does_not_exist_is_a_404(client: TestClient, registered):
+    assert client.get("/admin/tools/nope/edit").status_code == 404
+
+
+def test_new_is_not_parsed_as_a_tool_id(client: TestClient, registered):
+    """FastAPI matches in registration order; /admin/models has been bitten by
+    exactly this."""
+    response = client.get("/admin/tools/new")
+    assert response.status_code == 200
+    assert "New tool" in response.text
+
+
+# --- Creating and editing ----------------------------------------------------
+def test_creating_a_tool_then_editing_it(client: TestClient, db, registered):
+    _create(client, secret="s3cret")
+
+    tool = db.scalar(select(CustomTool))
+    assert tool.slug == "weather"
+    assert tool.headers_json == {"Accept": "application/json"}
+    assert tool.parameters_json["properties"]["city"] == {"type": "string"}
+    assert decrypt(tool.secret_encrypted) == "s3cret"
+    assert tool.enabled is True
+
+    client.post(
+        f"/admin/tools/{tool.id}",
+        data=_form(name="Forecast", enabled=None, secret=UNCHANGED_SENTINEL),
+        follow_redirects=False,
+    )
+    db.refresh(tool)
+    assert tool.name == "Forecast"
+    # An unticked checkbox is simply absent from the post, which is the signal.
+    assert tool.enabled is False
+    assert decrypt(tool.secret_encrypted) == "s3cret", "the dots must keep the secret"
+
+
+def test_clearing_the_field_removes_the_secret(client: TestClient, db, registered):
+    _create(client, secret="s3cret")
+    tool = db.scalar(select(CustomTool))
+
+    client.post(f"/admin/tools/{tool.id}", data=_form(secret=""), follow_redirects=False)
+    db.refresh(tool)
+    assert tool.secret_encrypted == ""
+
+
+def test_a_secret_is_never_rendered_in_full(client: TestClient, db, registered):
+    _create(client, secret="super-secret-value")
+    tool = db.scalar(select(CustomTool))
+
+    page = client.get(f"/admin/tools/{tool.id}/edit").text
+    assert "super-secret-value" not in page
+    assert UNCHANGED_SENTINEL in page
+
+
+# --- Validation reports back into the form -----------------------------------
+def test_bad_parameter_json_is_reported_not_a_422(client: TestClient, db, registered):
+    response = _create(client, parameters="{not json")
+    assert response.status_code == 200
+    assert "not valid JSON" in response.text
+    assert db.scalar(select(CustomTool)) is None
+
+
+def test_parameters_that_are_not_an_object_are_refused(client: TestClient, db, registered):
+    response = _create(client, parameters='{"type": "string"}')
+    assert "must be a JSON object" in response.text
+    assert db.scalar(select(CustomTool)) is None
+
+
+def test_a_slug_colliding_with_a_builtin_is_refused(client: TestClient, db, registered):
+    response = _create(client, slug="web_search")
+    assert "built-in tool" in response.text
+    assert db.scalar(select(CustomTool)) is None
+
+
+def test_a_duplicate_slug_is_refused(client: TestClient, db, registered):
+    _create(client)
+    response = _create(client, name="Other")
+    assert "already a tool" in response.text
+    assert len(list(db.scalars(select(CustomTool)))) == 1
+
+
+def test_a_url_whose_host_is_a_variable_is_refused(client: TestClient, db, registered):
+    response = _create(client, url_template="https://{{city}}.test/x")
+    assert "literal" in response.text
+    assert db.scalar(select(CustomTool)) is None
+
+
+def test_a_rejected_save_keeps_what_was_typed(client: TestClient, db, registered):
+    _create(client)
+    tool = db.scalar(select(CustomTool))
+
+    response = client.post(
+        f"/admin/tools/{tool.id}",
+        data=_form(name="Renamed", parameters="{oops"),
+        follow_redirects=False,
+    )
+    assert "Renamed" in response.text, "the form still holds the submitted name"
+    db.refresh(tool)
+    assert tool.name == "Weather", "and the stored row is untouched"
+
+
+# --- Access ------------------------------------------------------------------
+def test_making_a_tool_public_clears_its_groups(client: TestClient, db, registered):
+    group = Group(name="Council")
+    db.add(group)
+    db.commit()
+
+    _create(client, public=None, group_ids=group.id)
+    tool = db.scalar(select(CustomTool))
+    assert [g.name for g in tool.groups] == ["Council"]
+
+    client.post(
+        f"/admin/tools/{tool.id}",
+        data={**_form(public="true"), "group_ids": group.id},
+        follow_redirects=False,
+    )
+    db.refresh(tool)
+    assert tool.groups == []
+
+
+def test_a_restricted_tool_is_hidden_from_a_user_outside_its_groups(db, registered):
+    from lembas.services import tool_access
+
+    group = Group(name="Council")
+    outsider = User(name="Sam", email="s@shire.test", password_hash=hash_password("x"))
+    db.add_all([group, outsider])
+    db.add(
+        CustomTool(
+            slug="weather", name="Weather", url_template="https://api.test/", public=False
+        )
+    )
+    db.commit()
+
+    tool = db.scalar(select(CustomTool))
+    tool.groups = [group]
+    db.commit()
+
+    assert tool_access.visible_custom_tools(db, outsider) == []
+    outsider.groups = [group]
+    db.commit()
+    assert len(tool_access.visible_custom_tools(db, outsider)) == 1
+
+
+# --- Running one by hand -----------------------------------------------------
+def test_the_test_button_shows_what_the_model_would_read(
+    client: TestClient, db, registered, mock_http, monkeypatch
+):
+    monkeypatch.setattr(
+        "socket.getaddrinfo", lambda *a, **k: [(2, 1, 6, "", ("93.184.216.34", 80))]
+    )
+    mock_http(lambda _r: httpx.Response(200, json={"summary": "Sunny"}))
+    _create(client, response_mode="json", response_path="summary")
+    tool = db.scalar(select(CustomTool))
+
+    response = client.post(
+        f"/admin/tools/{tool.id}/test", data={"arguments": '{"city": "Minas Tirith"}'}
+    )
+    assert response.status_code == 200
+    assert "Sunny" in response.text
+
+
+def test_a_failing_test_is_recorded_on_the_row(
+    client: TestClient, db, registered, mock_http, monkeypatch
+):
+    monkeypatch.setattr(
+        "socket.getaddrinfo", lambda *a, **k: [(2, 1, 6, "", ("93.184.216.34", 80))]
+    )
+    mock_http(lambda _r: httpx.Response(503, text="down"))
+    _create(client)
+    tool = db.scalar(select(CustomTool))
+
+    client.post(f"/admin/tools/{tool.id}/test", data={"arguments": "{}"})
+    db.refresh(tool)
+    assert "503" in tool.last_error
+    assert tool.last_checked_at is not None
+
+
+def test_bad_test_arguments_are_reported(client: TestClient, db, registered):
+    _create(client)
+    tool = db.scalar(select(CustomTool))
+    response = client.post(f"/admin/tools/{tool.id}/test", data={"arguments": "[1, 2]"})
+    assert "JSON object" in response.text
+
+
+# --- The list ----------------------------------------------------------------
+def test_the_list_searches_and_filters(client: TestClient, db, registered):
+    _create(client)
+    _create(client, name="Tickets", slug="tickets", url_template="https://jira.test/{{city}}")
+    tool = db.scalar(select(CustomTool).where(CustomTool.slug == "tickets"))
+    tool.enabled = False
+    db.commit()
+
+    page = client.get("/admin/tools").text
+    assert "Weather" in page and "Tickets" in page
+
+    assert "Tickets" not in client.get("/admin/tools?filter=enabled").text
+    assert "Weather" not in client.get("/admin/tools?q=tick").text
+
+
+def test_deleting_a_tool_leaves_its_prompt_override_alone(client: TestClient, db, registered):
+    """The override outlives the row, which is what lets a tool be recreated
+    under the same slug without losing the wording somebody chose."""
+    from lembas.services import prompts as prompts_service
+
+    _create(client, guidance="- Default wording.")
+    tool = db.scalar(select(CustomTool))
+    prompts_service.save(db, {"tool.custom_weather": "- Edited wording."})
+
+    client.post(f"/admin/tools/{tool.id}/delete", follow_redirects=False)
+    assert db.scalar(select(CustomTool)) is None
+    assert prompts_service.stored(db)["tool.custom_weather"] == "- Edited wording."
+
+
+def test_the_secret_survives_a_round_trip_through_the_form(client: TestClient, db, registered):
+    """A regression guard on the sentinel: the field is rendered with dots, and
+    submitting the page unchanged must not overwrite the key with them."""
+    db.add(
+        CustomTool(
+            slug="weather",
+            name="Weather",
+            url_template="https://api.test/",
+            secret_encrypted=encrypt("s3cret"),
+        )
+    )
+    db.commit()
+    tool = db.scalar(select(CustomTool))
+
+    client.post(
+        f"/admin/tools/{tool.id}", data=_form(secret=UNCHANGED_SENTINEL), follow_redirects=False
+    )
+    db.refresh(tool)
+    assert decrypt(tool.secret_encrypted) == "s3cret"

tests/test_custom_tools.py

@@ -0,0 +1,382 @@
+"""Custom HTTP tools: filling the template, and refusing to be pointed elsewhere.
+
+Most of this file is about the second. The arguments come from a model, which
+can be talked into things by whatever it just read, so an argument filling a
+hole in a URL is the same kind of input as a URL typed by a stranger.
+"""
+
+from __future__ import annotations
+
+import json
+
+import httpx
+import pytest
+
+from lembas.db.models import (
+    RESPONSE_JSON,
+    RESPONSE_RAW,
+    RESPONSE_TEXT,
+    SECRET_BEARER,
+    SECRET_HEADER,
+    SECRET_NONE,
+    CustomTool,
+)
+from lembas.services import custom_tools
+from lembas.services.crypto import encrypt
+from lembas.services.fetch import FetchError
+
+
+@pytest.fixture(autouse=True)
+def dns(monkeypatch):
+    """Resolve invented hostnames to a public address.
+
+    `api.test` does not exist and `check_url` resolves for real, which is the
+    whole point of it. A literal IP is handed back as itself, so the tests that
+    check a private address are still checking one.
+    """
+    import ipaddress
+    import socket
+
+    def resolve(host, *_args, **_kwargs):
+        try:
+            ipaddress.ip_address(host)
+        except ValueError:
+            return [(2, 1, 6, "", ("93.184.216.34", 80))]
+        return [(2, 1, 6, "", (host, 80))]
+
+    monkeypatch.setattr(socket, "getaddrinfo", resolve)
+
+
+def _spec(**overrides) -> custom_tools.HttpSpec:
+    base = {
+        "slug": "weather",
+        "label": "Weather",
+        "method": "GET",
+        "url_template": "https://api.test/v1/city/{{city}}",
+        "secret_placement": SECRET_NONE,
+        "parameters": {
+            "type": "object",
+            "properties": {"city": {"type": "string"}, "days": {"type": "integer"}},
+            "required": ["city"],
+        },
+    }
+    return custom_tools.HttpSpec(**{**base, **overrides})
+
+
+def _ok(body: str = "sunny", *, status: int = 200, content_type: str = "text/plain"):
+    seen = {}
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        seen["request"] = request
+        seen.setdefault("urls", []).append(str(request.url))
+        return httpx.Response(status, text=body, headers={"content-type": content_type})
+
+    return handler, seen
+
+
+# --- Filling the URL ---------------------------------------------------------
+def test_an_argument_is_percent_encoded_into_the_url():
+    url = custom_tools.fill_url(_spec(), {"city": "Minas Tirith"})
+    assert url == "https://api.test/v1/city/Minas%20Tirith"
+
+
+def test_an_argument_cannot_add_a_path_segment_or_a_query():
+    """safe="" is the whole point. Everything structural encodes."""
+    url = custom_tools.fill_url(_spec(), {"city": "../../admin?token=x#y"})
+    assert "/admin" not in url
+    assert "?" not in url and "#" not in url
+    assert url.startswith("https://api.test/v1/city/")
+
+
+def test_an_argument_cannot_reach_another_host():
+    url = custom_tools.fill_url(_spec(), {"city": "evil.test/steal"})
+    assert url.startswith("https://api.test/")
+
+
+def test_an_undeclared_name_is_removed_rather_than_passed_through():
+    """Unlike the prompt fragments, where an unrecognised {{x}} is left alone.
+    A literal {{x}} in a URL is not a feature."""
+    spec = _spec(url_template="https://api.test/{{city}}/{{unknown}}")
+    assert custom_tools.fill_url(spec, {"city": "a", "unknown": "b"}) == "https://api.test/a/"
+
+
+def test_an_argument_the_model_did_not_send_becomes_nothing():
+    assert custom_tools.fill_url(_spec(), {}) == "https://api.test/v1/city/"
+
+
+def test_a_template_whose_host_is_a_variable_is_refused():
+    with pytest.raises(FetchError, match="literal"):
+        custom_tools.fill_url(_spec(url_template="https://{{city}}.test/x"), {"city": "a"})
+
+
+def test_a_template_that_is_not_http_is_refused():
+    with pytest.raises(FetchError):
+        custom_tools.fill_url(_spec(url_template="file:///etc/passwd"), {})
+
+
+# --- Reaching the network ----------------------------------------------------
+async def test_a_private_address_is_refused_unless_the_row_allows_it(mock_http):
+    handler, _seen = _ok()
+    mock_http(handler)
+
+    spec = _spec(url_template="http://127.0.0.1:11434/api/tags", parameters={})
+    refused = await custom_tools.call(spec, {})
+    assert refused.event["status"] == "error"
+    assert "private or local" in refused.event["error"]
+
+    allowed = await custom_tools.call(
+        _spec(
+            url_template="http://127.0.0.1:11434/api/tags", parameters={}, allow_private=True
+        ),
+        {},
+    )
+    assert allowed.event["status"] == "ok"
+
+
+async def test_a_hostname_resolving_to_loopback_is_refused(mock_http, monkeypatch):
+    """A name pointing at 127.0.0.1 walks past any check that only reads the
+    text of the URL."""
+    handler, _seen = _ok()
+    mock_http(handler)
+    monkeypatch.setattr(
+        "socket.getaddrinfo",
+        lambda *a, **k: [(2, 1, 6, "", ("127.0.0.1", 80))],
+    )
+
+    outcome = await custom_tools.call(_spec(parameters={}), {})
+    assert outcome.event["status"] == "error"
+    assert "private or local" in outcome.event["error"]
+
+
+async def test_every_redirect_hop_is_checked(mock_http, monkeypatch):
+    """httpx's own following would validate the first address and then happily
+    land on localhost."""
+    hops = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        hops.append(str(request.url))
+        if request.url.host == "api.test":
+            return httpx.Response(302, headers={"location": "http://inside.test/secrets"})
+        return httpx.Response(200, text="secrets")
+
+    mock_http(handler)
+
+    def resolve(host, *_args, **_kwargs):
+        if host == "inside.test":
+            return [(2, 1, 6, "", ("10.0.0.5", 80))]
+        return [(2, 1, 6, "", ("93.184.216.34", 80))]
+
+    monkeypatch.setattr("socket.getaddrinfo", resolve)
+
+    outcome = await custom_tools.call(_spec(parameters={}), {})
+    assert outcome.event["status"] == "error"
+    assert len(hops) == 1, "the second hop must never be requested"
+
+
+async def test_the_secret_is_dropped_on_a_cross_host_redirect(mock_http):
+    seen = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        seen.append((request.url.host, request.headers.get("authorization")))
+        if request.url.host == "api.test":
+            return httpx.Response(302, headers={"location": "https://elsewhere.test/x"})
+        return httpx.Response(200, text="ok")
+
+    mock_http(handler)
+
+    outcome = await custom_tools.call(
+        _spec(parameters={}, secret="s3cret", secret_placement=SECRET_BEARER), {}
+    )
+    assert outcome.event["status"] == "ok"
+    assert seen[0] == ("api.test", "Bearer s3cret")
+    assert seen[1] == ("elsewhere.test", None)
+
+
+async def test_a_bearer_secret_reaches_the_request_and_never_the_event(mock_http):
+    handler, seen = _ok()
+    mock_http(handler)
+
+    outcome = await custom_tools.call(
+        _spec(parameters={}, secret="s3cret", secret_placement=SECRET_BEARER), {}
+    )
+    assert seen["request"].headers["authorization"] == "Bearer s3cret"
+    assert "s3cret" not in json.dumps(outcome.event)
+
+
+async def test_a_header_secret_uses_the_name_it_was_given(mock_http):
+    handler, seen = _ok()
+    mock_http(handler)
+
+    await custom_tools.call(
+        _spec(
+            parameters={},
+            secret="k",
+            secret_placement=SECRET_HEADER,
+            secret_name="X-Api-Key",
+        ),
+        {},
+    )
+    assert seen["request"].headers["x-api-key"] == "k"
+
+
+async def test_a_header_value_cannot_carry_a_newline(mock_http):
+    handler, seen = _ok()
+    mock_http(handler)
+
+    await custom_tools.call(
+        _spec(headers={"X-Trace": "{{city}}"}), {"city": "a\r\nX-Admin: yes"}
+    )
+    assert "\n" not in seen["request"].headers["x-trace"]
+
+
+async def test_a_body_argument_cannot_end_the_json_string(mock_http):
+    handler, seen = _ok()
+    mock_http(handler)
+
+    await custom_tools.call(
+        _spec(
+            method="POST",
+            url_template="https://api.test/v1/ask",
+            body_template='{"city": "{{city}}"}',
+        ),
+        {"city": 'x", "admin": "yes'},
+    )
+    body = json.loads(seen["request"].content)
+    assert set(body) == {"city"}
+
+
+# --- Reading the response ----------------------------------------------------
+async def test_a_json_response_is_narrowed_by_the_path(mock_http):
+    def handler(_request):
+        return httpx.Response(
+            200,
+            json={"data": {"items": [{"title": "Mallorn"}, {"title": "Elanor"}]}},
+        )
+
+    mock_http(handler)
+    outcome = await custom_tools.call(
+        _spec(parameters={}, response_mode=RESPONSE_JSON, response_path="data.items.0.title"), {}
+    )
+    assert outcome.content == "Mallorn"
+
+
+async def test_a_path_that_leads_nowhere_yields_the_whole_document(mock_http):
+    mock_http(lambda _r: httpx.Response(200, json={"a": 1}))
+    outcome = await custom_tools.call(
+        _spec(parameters={}, response_mode=RESPONSE_JSON, response_path="nope.nope"), {}
+    )
+    assert json.loads(outcome.content) == {"a": 1}
+
+
+async def test_an_html_response_becomes_text(mock_http):
+    handler, _seen = _ok(
+        "<html><head><title>T</title></head><body><p>Hello</p></body></html>",
+        content_type="text/html",
+    )
+    mock_http(handler)
+    outcome = await custom_tools.call(_spec(parameters={}, response_mode=RESPONSE_TEXT), {})
+    assert outcome.content == "Hello"
+
+
+async def test_a_raw_response_is_left_alone(mock_http):
+    handler, _seen = _ok("<p>kept</p>", content_type="text/html")
+    mock_http(handler)
+    outcome = await custom_tools.call(_spec(parameters={}, response_mode=RESPONSE_RAW), {})
+    assert outcome.content == "<p>kept</p>"
+
+
+async def test_the_response_is_capped_and_says_so(mock_http):
+    handler, _seen = _ok("x" * 5000)
+    mock_http(handler)
+    outcome = await custom_tools.call(_spec(parameters={}, max_chars=500), {})
+    assert len(outcome.content) < 600
+    assert outcome.content.endswith("(truncated)")
+
+
+async def test_the_event_preview_is_capped_independently(mock_http):
+    """`max_chars` is spent once; the event is stored on the message row."""
+    handler, _seen = _ok("x" * 30_000)
+    mock_http(handler)
+    outcome = await custom_tools.call(_spec(parameters={}, max_chars=20_000), {})
+    assert len(outcome.event["text"]) <= custom_tools.MAX_EVENT_CHARS
+    assert len(outcome.content) > custom_tools.MAX_EVENT_CHARS
+
+
+async def test_an_http_error_becomes_an_explanation_not_an_exception(mock_http):
+    handler, _seen = _ok("no such city", status=404)
+    mock_http(handler)
+    outcome = await custom_tools.call(_spec(parameters={}), {})
+    assert outcome.event["status"] == "error"
+    assert "404" in outcome.content
+    assert "no such city" in outcome.content
+
+
+async def test_a_transport_failure_is_reported_to_the_model(mock_http):
+    def handler(request):
+        raise httpx.ConnectTimeout("too slow", request=request)
+
+    mock_http(handler)
+    outcome = await custom_tools.call(_spec(parameters={}), {})
+    assert outcome.event["status"] == "error"
+    assert "Could not reach" in outcome.content
+
+
+async def test_the_event_names_the_host_and_not_the_filled_url(mock_http):
+    """A path segment carries an argument, and the event is rendered and kept."""
+    handler, _seen = _ok()
+    mock_http(handler)
+    outcome = await custom_tools.call(_spec(), {"city": "Minas Tirith"})
+    assert outcome.event["detail"] == "GET api.test"
+    assert "Minas" not in outcome.event["detail"]
+    assert "Minas Tirith" in outcome.event["query"]
+
+
+# --- Turning rows into tools -------------------------------------------------
+def _row(db, **overrides) -> CustomTool:
+    row = CustomTool(
+        **{
+            "slug": "weather",
+            "name": "Weather",
+            "description": "Look up the weather.",
+            "url_template": "https://api.test/{{city}}",
+            "parameters_json": {"type": "object", "properties": {"city": {"type": "string"}}},
+            **overrides,
+        }
+    )
+    db.add(row)
+    db.commit()
+    return row
+
+
+def test_a_row_becomes_a_tool_definition(db, user_id):
+    from lembas.db.models import User
+
+    _row(db)
+    defs = custom_tools.tool_defs(db, db.get(User, user_id))
+    assert [tool.name for tool in defs] == ["weather"]
+    assert defs[0].family == "custom:weather"
+    assert defs[0].schema["function"]["description"] == "Look up the weather."
+
+
+def test_a_disabled_row_is_not_offered(db, user_id):
+    from lembas.db.models import User
+
+    _row(db, enabled=False)
+    assert custom_tools.tool_defs(db, db.get(User, user_id)) == []
+
+
+def test_a_schema_that_is_not_an_object_is_replaced(db, user_id):
+    """An endpoint rejects the whole request over a malformed tools array, so
+    one bad row must not take the reply with it."""
+    from lembas.db.models import User
+
+    _row(db, parameters_json={"type": "string"})
+    defs = custom_tools.tool_defs(db, db.get(User, user_id))
+    assert defs[0].parameters == {"type": "object", "properties": {}}
+
+
+def test_the_secret_is_decrypted_into_the_snapshot_and_nowhere_else(db):
+    row = _row(db, secret_encrypted=encrypt("s3cret"))
+    spec = custom_tools.spec_from(row)
+    assert spec.secret == "s3cret"
+    assert "s3cret" not in row.secret_encrypted

tests/test_harness.py

@@ -54,6 +54,27 @@ def test_only_the_guidance_for_offered_tools_appears(db, owner):
     assert "Skills are procedures" not in text
 
 
+def test_a_custom_tools_guidance_appears_only_when_it_is_offered(db, owner):
+    """The row supplies the default, and the fragment is gated on the tool's own
+    family -- which is why the registry had to stop being a module constant."""
+    from lembas.db.models import CustomTool
+
+    db.add(
+        CustomTool(
+            slug="weather",
+            name="Weather",
+            description="Look up the weather.",
+            url_template="https://api.test/{{city}}",
+            guidance="- Check the weather rather than guessing at it.",
+        )
+    )
+    db.commit()
+
+    offered = tools_service.registry(db)["weather"].schema
+    assert "Check the weather" in harness.compose(db, owner, [offered])
+    assert "Check the weather" not in harness.compose(db, owner, _tools("web_search"))
+
+
 def test_the_memory_block_is_included_when_memory_is_offered(db, owner):
     memories_service.add(db, owner=owner, content="Prefers metric units.")
     text = harness.compose(db, owner, _tools("memory_add"))

tests/test_tool_activity.py

@@ -0,0 +1,124 @@
+"""Rendering what a tool did.
+
+The block is written from four places and read from stored rows written by
+earlier versions, so it has to render anything shaped roughly like an event --
+and everything in it is third-party text.
+"""
+
+from __future__ import annotations
+
+from lembas.web.templating import templates
+
+
+def _render(*events, live: bool = False) -> str:
+    return templates.get_template("chat/_tool_activity.html").render(
+        {"tool_events": list(events), "live": live}
+    )
+
+
+def test_a_search_still_says_it_searched_the_web():
+    html = _render(
+        {
+            "name": "web_search",
+            "kind": "search",
+            "query": "mallorn",
+            "status": "ok",
+            "results": [
+                {
+                    "title": "Mallorn",
+                    "url": "https://a.test/m",
+                    "host": "a.test",
+                    "snippet": "A tree.",
+                }
+            ],
+        }
+    )
+    assert "Searched the web for “mallorn”" in html
+    assert '<a class="tool-result__title" href="https://a.test/m"' in html
+    assert "1 result" in html
+
+
+def test_a_library_tool_no_longer_claims_to_have_searched_the_web():
+    """Stored rows predate `kind`, and every one of them used to render a globe
+    and "Searched the web for <the note title>"."""
+    html = _render({"name": "notes_search", "query": "shopping", "status": "ok", "results": []})
+    assert "Searched the web" not in html
+    assert "notes_search" in html
+
+
+def test_a_custom_tool_is_named_and_its_host_shown():
+    html = _render(
+        {
+            "name": "weather",
+            "kind": "custom",
+            "label": "Weather",
+            "query": "city='Minas Tirith'",
+            "detail": "GET api.test",
+            "status": "ok",
+            "results": [],
+            "text": "Sunny.",
+        }
+    )
+    assert "Weather" in html
+    assert "GET api.test" in html
+    assert "Sunny." in html
+
+
+def test_a_tools_own_text_is_escaped_and_never_rendered_as_markdown():
+    """Hard rule 6. A tool's reply is exactly as untrusted as a search result,
+    and markdown is the one path allowed to emit HTML."""
+    html = _render(
+        {
+            "name": "weather",
+            "kind": "custom",
+            "label": "Weather",
+            "status": "ok",
+            "results": [],
+            "text": "<img src=x onerror=alert(1)> [click](javascript:alert(1))",
+        }
+    )
+    assert "<img" not in html
+    assert "&lt;img" in html
+    # The markdown link is shown as the text it is, not turned into an anchor.
+    assert "<a " not in html
+    assert "[click](javascript:alert(1))" in html
+
+
+def test_a_result_url_that_is_not_http_never_becomes_a_link():
+    html = _render(
+        {
+            "name": "web_search",
+            "kind": "search",
+            "status": "ok",
+            "results": [{"title": "Bad", "url": "javascript:alert(1)", "host": "", "snippet": ""}],
+        }
+    )
+    assert "<a " not in html
+    assert '<span class="tool-result__title">Bad</span>' in html
+
+
+def test_a_result_with_no_url_at_all_does_not_explode():
+    html = _render(
+        {
+            "name": "notes_search",
+            "status": "ok",
+            "results": [{"title": "A note", "id": "abc"}],
+        }
+    )
+    assert "A note" in html
+
+
+def test_a_failure_shows_its_reason():
+    html = _render(
+        {
+            "name": "weather",
+            "kind": "custom",
+            "label": "Weather",
+            "status": "error",
+            "error": "HTTP 503",
+            "results": [],
+        }
+    )
+    assert "tool-activity--error" in html
+    assert "Weather failed" in html
+    assert "HTTP 503" in html

tests/test_tools.py

@@ -166,6 +166,57 @@ def _context(**kwargs):
     return tools_service.ToolContext(owner_id="someone", **kwargs)
 
 
+# --- The offer and the runner travel together --------------------------------
+def test_the_resolved_set_carries_the_runners_with_the_schemas(db, user_id):
+    """A tool that is a database row is not reachable through the import-time
+    registry, so the resolution has to travel with the offer."""
+    settings_store.update(db, {"enabled": True}, key=settings_store.SEARCH)
+    chat = _chat_with(db, user_id, capabilities={"tools": True})
+    resolved = tools_service.resolve_tools(db, chat, _user(db, user_id))
+
+    assert _names(resolved.schemas) == set(resolved.by_name)
+    assert all(callable(tool.run) for tool in resolved.defs)
+    # The old accessor is the same set, so nothing that only wants schemas moved.
+    assert resolved.schemas == tools_service.enabled_tools(db, chat, _user(db, user_id))
+
+
+async def test_a_tool_that_was_not_offered_is_refused(db, user_id):
+    """The lookup is against what was offered, not against everything that
+    exists. A model naming a tool its chat was gated out of used to have it run,
+    because only the offer was ever filtered."""
+    from lembas.db.models import User
+    from lembas.services.library import notes as notes_service
+
+    owner = db.get(User, user_id)
+    note = notes_service.create(db, owner=owner, title="Keep me", body="...")
+
+    chat = _chat_with(db, user_id, capabilities={"tools": True, "tool_notes": False})
+    resolved = tools_service.resolve_tools(db, chat, owner)
+    context = tools_service.context_for(db, owner, chat, tools=resolved)
+
+    outcome = await tools_service.run_tool(
+        context, "notes_delete", json.dumps({"id": note.id})
+    )
+    assert outcome.event["status"] == "error"
+    assert notes_service.get(db, note.id, owner) is not None
+
+
+async def test_a_context_with_no_toolset_still_finds_the_builtins(monkeypatch):
+    """None means nobody resolved a set. An empty dict does not -- it means
+    nothing was offered, and is authoritative."""
+
+    async def fake_run(_config, query, *, limit=None):
+        return [SearchResult("A title", "https://a.test", "a snippet")]
+
+    monkeypatch.setattr("lembas.services.search.run", fake_run)
+
+    unresolved = await tools_service.run_tool(_context(), "web_search", '{"query": "x"}')
+    assert unresolved.event["status"] == "ok"
+
+    empty = await tools_service.run_tool(_context(tools={}), "web_search", '{"query": "x"}')
+    assert empty.event["status"] == "error"
+
+
 # --- Knowledge is scoped to the chat's bases ---------------------------------
 async def test_knowledge_search_is_limited_to_the_attached_bases(db, user_id):
     """"Answer from the contracts folder" is a different question from "answer