Reading the answer instead of asking somebody to know it

llama-server publishes the loaded model's Jinja chat template on /props, and
that template is the very thing that rejects a reasoning effort it does not
recognise -- so the accepted set is written down, authoritatively, in a place
this application can simply read. There is a button on the model's page that
does.

The parser handles both shapes a template uses: the values inline in the test
that rejects them (Bonsai), and a named list set elsewhere with nothing near
the mention spelling them out (gpt-oss). It is deliberately conservative,
because a wrong answer here silently removes a level somebody is entitled to:
only known efforts count, an unrelated list of quoted strings is ignored, and a
single match is read as a default -- `{%- set reasoning_effort = 'medium' %}`
-- rather than as a vocabulary of one.

An endpoint with no such route says so. OpenAI and vLLM do not publish a
template, and "this cannot tell us" must not be recorded as "this model accepts
nothing".

/props sits at the server root, beside the OpenAI-compatible surface rather
than inside it, so a base URL written as .../v1 needs the suffix stripped.
Getting that wrong is a silent 404 that looks like detection simply not
working, so there is a test on it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -16,6 +16,17 @@ for 1.0.0 have something to be assembled from.
 
 ## Unreleased
 
+## 1.3.0
+
+- **A model's reasoning efforts can now be detected rather than known.** There
+  is a button on the model's page that asks the endpoint what its chat template
+  actually accepts, and ticks those. llama.cpp publishes the loaded model's
+  template, and that template is the very thing that rejects an effort it does
+  not recognise — so the answer is read from the place that is authoritative
+  instead of guessed at, or discovered by a failed reply.
+- Endpoints that do not publish a template — OpenAI, vLLM — say so plainly
+  rather than being recorded as accepting nothing.
+
 ## 1.2.0
 
 - Fixed: **choosing a reasoning effort could kill the reply outright**, with a

src/lembas/__init__.py

@@ -1,3 +1,3 @@
 """LLeMbas - a Middle-earth themed web UI for OpenAI-compatible LLM endpoints."""
 
-__version__ = "1.2.0"
+__version__ = "1.3.0"

src/lembas/api/admin_models.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import contextlib
 import logging
+from urllib.parse import quote
 
 from fastapi import APIRouter, File, Form, HTTPException, Request, Response, UploadFile, status
 from fastapi.responses import FileResponse, RedirectResponse
@@ -162,7 +163,13 @@ async def models_page(
 
 @router.get("/admin/models/{model_id}/edit")
 async def model_detail(
-    request: Request, db: Db, user: AdminUser, model_id: str, saved: str = ""
+    request: Request,
+    db: Db,
+    user: AdminUser,
+    model_id: str,
+    saved: str = "",
+    detected: str = "",
+    message: str = "",
 ):
     """Everything about one model, on its own page."""
     model = _model(db, model_id)
@@ -182,6 +189,11 @@ async def model_detail(
             # current answer, which is the common three until somebody says.
             "efforts": chat_service.EFFORTS,
             "model_efforts": chat_service.efforts_for(model),
+            # What `detect-efforts` found, if it has just run. Escaped by the
+            # template like every other value; it is prose the endpoint or this
+            # application wrote, not markup.
+            "detected": detected if detected in ("success", "warning") else "",
+            "detected_message": message[:400],
             # Rows predating the split have no tool_* keys at all. Showing them
             # unticked would be a lie: tools.enabled_tools treats absent as on
             # when `tools` is on, so that an upgrade does not silently take web
@@ -342,6 +354,55 @@ async def move_model(
     return RedirectResponse(back or "/admin/models", status_code=303)
 
 
+@router.post("/admin/models/{model_id}/detect-efforts")
+async def detect_efforts(db: Db, user: AdminUser, model_id: str) -> Response:
+    """Ask the endpoint which reasoning efforts this model actually takes.
+
+    llama-server hands its loaded model's Jinja chat template over on `/props`,
+    and that template is the thing that rejects an effort it does not know -- so
+    the accepted set is written down in the one place that is authoritative,
+    rather than having to be guessed at or discovered by a failed reply.
+
+    Anything that is not a llama-server answers nothing here, and that is a
+    normal outcome: OpenAI and vLLM have no such route, and their models are
+    documented rather than introspectable. The result then says so instead of
+    claiming the model accepts nothing.
+    """
+    from lembas.services.llm.openai_client import Endpoint, fetch_chat_template
+
+    model = _model(db, model_id)
+    connection = db.get(Connection, model.connection_id)
+    if connection is None:
+        raise HTTPException(status.HTTP_404_NOT_FOUND, "That connection no longer exists.")
+
+    template = await fetch_chat_template(Endpoint.from_connection(connection))
+    found = chat_service.efforts_from_chat_template(template)
+
+    if found:
+        model.reasoning_efforts = found
+        db.commit()
+        message = "This model's template accepts: " + ", ".join(found) + "."
+        kind = "success"
+    elif template:
+        message = (
+            "The endpoint gave up its chat template, but nothing in it names a "
+            "set of reasoning efforts. Either this model does not take one, or "
+            "it accepts anything and never checks."
+        )
+        kind = "warning"
+    else:
+        message = (
+            "This endpoint does not publish its chat template, so there is "
+            "nothing to read. llama.cpp does; OpenAI and vLLM do not."
+        )
+        kind = "warning"
+
+    return RedirectResponse(
+        f"/admin/models/{model.id}/edit?detected={kind}&message={quote(message)}",
+        status_code=status.HTTP_303_SEE_OTHER,
+    )
+
+
 @router.post("/admin/models/{model_id}/default")
 async def set_default_model(
     db: Db, user: AdminUser, model_id: str, back: str = Form("")

src/lembas/services/chat.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import logging
+import re
 from datetime import UTC, datetime, timedelta
 from typing import Any
 
@@ -470,6 +471,66 @@ def resolved_effort(chat) -> str:
     return value if value in EFFORTS else ""
 
 
+def efforts_from_chat_template(template: str) -> list[str]:
+    """Which efforts a model's Jinja chat template will actually accept.
+
+    The template is where the truth lives: the one on a Bonsai reads roughly
+
+        {%- if reasoning_effort not in ('xhigh', 'medium', 'low') %}
+          {{- raise_exception('Unexpected reasoning effort ' ~ reasoning_effort ...
+
+    so the accepted set is written out beside the thing that rejects everything
+    else. `llama-server` hands the whole template over on `/props`, which makes
+    this readable rather than guessable.
+
+    Deliberately conservative, because a wrong answer here silently removes a
+    level somebody is entitled to:
+
+    - only quoted literals within a short window of a `reasoning_effort`
+      mention are considered, so an unrelated list elsewhere in a four-hundred
+      line template cannot contribute;
+    - the result is intersected with `EFFORTS`, so an unknown token is dropped
+      rather than stored;
+    - fewer than two survivors is treated as "the template did not say". One
+      match is far more likely to be a default assignment
+      (`{%- set reasoning_effort = 'medium' %}`) than a vocabulary.
+
+    Returns [] when nothing can be read, which every caller treats as "ask
+    somebody" rather than as "this model accepts nothing".
+    """
+    if not template or "reasoning_effort" not in template:
+        return []
+
+    found: set[str] = set()
+
+    # Shape one: the values sit in the statement that tests them.
+    #     {%- if reasoning_effort not in ('xhigh', 'medium', 'low') %}
+    for match in re.finditer(r"reasoning_effort", template):
+        window = template[match.start() : match.start() + 400]
+        # Stop at the end of the statement that mentions it, so a later,
+        # unrelated block cannot leak in.
+        window = window.split("%}")[0] if "%}" in window else window
+        for literal in re.findall(r"""['"]([a-z]{3,8})['"]""", window):
+            if literal in EFFORTS:
+                found.add(literal)
+
+    # Shape two: the values are a named list somewhere else, and the test says
+    #     {%- if reasoning_effort not in valid_efforts %}
+    # so nothing near the mention names them. Any group of quoted literals in
+    # which *every* token is a known effort and there are at least two is taken
+    # -- that is a strong enough signal on its own, and a list of nothing but
+    # effort names that is not the effort vocabulary would be a strange thing
+    # for a chat template to contain.
+    for group in re.findall(r"[\[(]((?:\s*['\"][a-z]{3,8}['\"]\s*,?)+)[\])]", template):
+        literals = re.findall(r"""['"]([a-z]{3,8})['"]""", group)
+        if len(literals) >= 2 and all(value in EFFORTS for value in literals):
+            found.update(literals)
+
+    if len(found) < 2:
+        return []
+    return [effort for effort in EFFORTS if effort in found]
+
+
 def apply_effort(
     body: dict[str, Any], effort: str | None, supported: tuple[str, ...] | None = None
 ) -> None:

src/lembas/services/llm/openai_client.py

@@ -68,6 +68,19 @@ class Endpoint:
             base = f"{base}/v1"
         return f"{base}/{path.lstrip('/')}"
 
+    def root_url(self, path: str) -> str:
+        """A URL at the *server's* root rather than under `/v1`.
+
+        llama-server's own endpoints -- `/props` is the one that matters here --
+        sit beside the OpenAI-compatible surface, not inside it. A base URL may
+        be written either way (`http://host:8080` or `.../v1`), so the suffix is
+        stripped rather than assumed absent.
+        """
+        base = self.base_url.rstrip("/")
+        if base.endswith("/v1"):
+            base = base[: -len("/v1")]
+        return f"{base}/{path.lstrip('/')}"
+
     def headers(self) -> dict[str, str]:
         headers = {"Content-Type": "application/json", **self.extra_headers}
         # Local endpoints frequently need no key at all; sending an empty
@@ -77,6 +90,30 @@ class Endpoint:
         return headers
 
 
+async def fetch_chat_template(endpoint: Endpoint) -> str:
+    """The model's own Jinja chat template, from llama-server's `/props`.
+
+    The one place the truth about a model's accepted values is actually
+    written down: `/props` returns `chat_template` verbatim, and that template
+    is what raises when it meets a `reasoning_effort` it does not know.
+
+    Returns "" rather than raising for anything that is not a llama-server --
+    OpenAI, vLLM and the rest have no such route, and "this endpoint cannot
+    tell us" is a normal answer here, not a failure.
+    """
+    try:
+        async with httpx.AsyncClient(timeout=10.0) as client:
+            response = await client.get(
+                endpoint.root_url("props"), headers=endpoint.headers()
+            )
+            response.raise_for_status()
+            payload = response.json()
+    except (httpx.HTTPError, ValueError, json.JSONDecodeError):
+        return ""
+    template = payload.get("chat_template") if isinstance(payload, dict) else ""
+    return template if isinstance(template, str) else ""
+
+
 def describe_http_error(exc: httpx.HTTPStatusError) -> str:
     """Turn an upstream error response into something worth reading.
 

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

@@ -115,6 +115,31 @@
         </label>
         {% endfor %}
       </div>
+      {% if detected %}
+      <div class="alert alert--{{ 'success' if detected == 'success' else 'warning' }}"
+           role="status">
+        {{ icon('sparkle' if detected == 'success' else 'warning', 'alert__icon') }}
+        <span>{{ detected_message }}</span>
+      </div>
+      {% endif %}
+
+      {#
+        Reading the answer rather than asking somebody to know it. llama-server
+        publishes the loaded model's Jinja chat template on `/props`, and that
+        template is the thing that rejects an effort it does not recognise --
+        so the accepted set is written down in the one authoritative place.
+        Endpoints without that route (OpenAI, vLLM) say so rather than
+        pretending the model accepts nothing.
+
+        Its own form, because this page's main form is a PUT of everything and
+        a detect must not carry half-edited fields with it.
+      #}
+      <form method="post" action="/admin/models/{{ model.id }}/detect-efforts">
+        <button class="btn btn--sm" type="submit">
+          {{ icon('search', 'icon--sm') }} Detect from the endpoint
+        </button>
+      </form>
+
       <p class="field__hint">
         The vocabulary is <strong>not the same for every model</strong>, and
         sending one a model does not know is not ignored — it is rendered into

tests/test_effort.py

@@ -456,3 +456,129 @@ def test_a_model_with_no_advertisement_simply_loses_the_refused_value():
     from lembas.services import generation
 
     assert generation._advertised_efforts("Unexpected reasoning effort high.") == []
+
+
+# --- Reading the answer instead of asking somebody to know it ----------------
+#
+# llama-server publishes the loaded model's Jinja chat template on /props, and
+# that template is the thing that rejects an effort it does not know -- so the
+# accepted set is written down in the one authoritative place.
+BONSAI_TEMPLATE = (
+    "{%- if reasoning_effort not in ('xhigh', 'medium', 'low') %}"
+    "{{- raise_exception('Unexpected reasoning effort ' ~ reasoning_effort ~ "
+    "'. Supported types are xhigh (default), medium, and low.') }}{%- endif %}"
+)
+GPT_OSS_TEMPLATE = (
+    '{%- set valid_efforts = ["low", "medium", "high"] %}'
+    "{%- if reasoning_effort not in valid_efforts %}"
+    "{{ raise_exception('bad effort') }}{% endif %}"
+)
+
+
+def test_the_accepted_set_is_read_out_of_the_template():
+    from lembas.services import chat as chat_service
+
+    assert chat_service.efforts_from_chat_template(BONSAI_TEMPLATE) == [
+        "low", "medium", "xhigh",
+    ]
+
+
+def test_a_template_that_keeps_its_list_in_a_variable_is_read_too():
+    """gpt-oss names the list rather than inlining it, so nothing near the
+    `reasoning_effort` mention spells the values out."""
+    from lembas.services import chat as chat_service
+
+    assert chat_service.efforts_from_chat_template(GPT_OSS_TEMPLATE) == [
+        "low", "medium", "high",
+    ]
+
+
+def test_an_unrelated_list_is_not_mistaken_for_a_vocabulary():
+    from lembas.services import chat as chat_service
+
+    template = '{%- set roles = ["user", "assistant", "system"] %}{{ messages }}'
+    assert chat_service.efforts_from_chat_template(template) == []
+
+
+def test_a_single_mention_is_not_a_vocabulary():
+    """`{%- set reasoning_effort = 'medium' %}` is a default, not a list, and
+    reading it as one would leave a model offering exactly one level."""
+    from lembas.services import chat as chat_service
+
+    assert chat_service.efforts_from_chat_template("{%- set reasoning_effort = 'medium' %}") == []
+
+
+def test_a_template_that_says_nothing_says_nothing():
+    from lembas.services import chat as chat_service
+
+    assert chat_service.efforts_from_chat_template("") == []
+    assert chat_service.efforts_from_chat_template("{{ messages }}") == []
+
+
+def test_props_lives_beside_the_openai_surface_not_inside_it():
+    """`/props` is llama-server's own route, at the server root -- a base URL
+    written as `.../v1` would otherwise ask for `/v1/props`, which is a 404."""
+    from lembas.services.llm.openai_client import Endpoint
+
+    endpoint = Endpoint(base_url="http://host:8080/v1", api_key="", extra_headers={})
+    assert endpoint.root_url("props") == "http://host:8080/props"
+
+    bare = Endpoint(base_url="http://host:8080", api_key="", extra_headers={})
+    assert bare.root_url("props") == "http://host:8080/props"
+    # And the OpenAI surface is unchanged by any of this.
+    assert bare.url("chat/completions") == "http://host:8080/v1/chat/completions"
+
+
+def test_detecting_from_the_endpoint_writes_the_list(client, db, registered, mock_http):
+    """The whole path: a button, a GET to /props, the template parsed, the
+    model's list written."""
+    import httpx
+    from sqlalchemy import select
+
+    from lembas.db.models import Connection, Model
+
+    connection = Connection(name="local", base_url="http://127.0.0.1:1", api_key_encrypted="")
+    db.add(connection)
+    db.commit()
+    db.add(Model(connection_id=connection.id, model_id="bonsai"))
+    db.commit()
+    model = db.scalar(select(Model).where(Model.model_id == "bonsai"))
+
+    asked: list[str] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        asked.append(str(request.url))
+        return httpx.Response(200, json={"chat_template": BONSAI_TEMPLATE})
+
+    mock_http(handler)
+    response = client.post(
+        f"/admin/models/{model.id}/detect-efforts", follow_redirects=False
+    )
+    assert response.status_code == 303
+
+    db.expire_all()
+    assert db.get(Model, model.id).reasoning_efforts == ["low", "medium", "xhigh"]
+    # At the server root, not under /v1.
+    assert asked and asked[0].endswith("/props")
+
+
+def test_an_endpoint_with_no_props_leaves_the_list_alone(client, db, registered, mock_http):
+    """OpenAI and vLLM have no such route, and "this cannot tell us" must not
+    be recorded as "this model accepts nothing"."""
+    import httpx
+    from sqlalchemy import select
+
+    from lembas.db.models import Connection, Model
+
+    connection = Connection(name="hosted", base_url="http://127.0.0.1:2", api_key_encrypted="")
+    db.add(connection)
+    db.commit()
+    db.add(Model(connection_id=connection.id, model_id="gpt-x", reasoning_efforts=["low", "high"]))
+    db.commit()
+    model = db.scalar(select(Model).where(Model.model_id == "gpt-x"))
+
+    mock_http(lambda request: httpx.Response(404, json={"error": "not found"}))
+    client.post(f"/admin/models/{model.id}/detect-efforts", follow_redirects=False)
+
+    db.expire_all()
+    assert db.get(Model, model.id).reasoning_efforts == ["low", "high"]