diff --git a/docs/architecture/local-models/selection.md b/docs/architecture/local-models/selection.md
index 4f41538bb5..94aef63737 100644
--- a/docs/architecture/local-models/selection.md
+++ b/docs/architecture/local-models/selection.md
@@ -238,6 +238,13 @@ a `json_schema` request, which
 some templates, is retried once unconstrained. Chat prose is deliberately
 unconstrained.
 
+Studio passes a schema through `run_model()`
+([`generate.py`](../../../surfsense_local/backend/worker/studio/shared/generate.py)),
+each format's beside its prompts, as the quiz's
+([`schema.py`](../../../surfsense_local/backend/worker/studio/content/quiz/schema.py)).
+A reply that arrives unconstrained, from an endpoint that ignores
+`response_format` or from the 400 retry, is still read by `parse_json()`.
+
 ## How it is tested
 
 [`surfsense_local/backend/tests/unit/llm/profile/`](../../../surfsense_local/backend/tests/unit/llm/profile/)
@@ -252,6 +259,6 @@ over HTTP.
 - The tier fallback keys on the provider name, not on loopback: `Fingerprint.local` is `provider == "llamacpp"`, so a local endpoint reached through a connection falls to `capable` when nothing else is known; the decision is to key on `host_destination()`, which already computes loopback.
 - A remote listing row with no `hugging_face_id` always sets `vendor` (to `owned_by`, or to the id's prefix even when that is empty) and never reads the size in the name, so such a model is classified `frontier`: a `qwen3-4b` from a local endpoint whose listing carries no `hugging_face_id` gets frontier prompts. Featherless lists every model this way (`"owned_by": "Feather"`, no `hugging_face_id`), so every model there, Qwen3 0.6B included, gets frontier prompts.
 - Local fingerprints come from the filename only: `LlamaCppProvider` has no `inspect()`, so `from_llamacpp()`, which reads `general.parameter_count` from `/props`, is never called.
-- No caller passes `json_schema`: the providers support constrained decoding, but no Studio format or chat call uses it, so format compliance still depends on the prompt.
+- Only the quiz passes `json_schema`: mind map, flashcards, HTML, image, infographic and the podcast's outline and draft still ask for JSON in the prompt alone, so their format compliance depends on it.
 - Chat cannot send an image: `Message.content` is a `str`, so even a model with `vision` has no way to receive one.
 - Nothing measures whether three tiers are still needed; once constrained decoding carries format compliance, a tier would carry reasoning depth only, which plausibly collapses three tiers to two.
diff --git a/docs/architecture/studio.md b/docs/architecture/studio.md
index 5a61e19358..9390a1b744 100644
--- a/docs/architecture/studio.md
+++ b/docs/architecture/studio.md
@@ -53,7 +53,7 @@ Eight formats follow it:
 - **summary**: the model's markdown is the body, titled by its first `# ` heading.
 - **mindmap**: JSON nodes, at most 10 branches, become a markdown outline, an H1 over nested bullets, which Markmap draws on the client and which stays readable as text.
 - **flashcards**: JSON cards, at most 20, become a deck JSON file and a markdown body.
-- **quiz**: JSON questions, at most 10, each kept only with exactly four options and an answer among them, become a quiz JSON file and a markdown body.
+- **quiz**: JSON questions, written under a schema ([`schema.py`](../../surfsense_local/backend/worker/studio/content/quiz/schema.py)), at most 10, each kept only with exactly four options and an answer among them, become a quiz JSON file and a markdown body.
 - **html**: a JSON title and sections, at most 10. Every value is HTML-escaped into a fixed template, so the page cannot carry a script.
 - **podcast**: the model outlines the episode from the brief, then drafts it segment by segment, each reply capped at 12 tokens per word of the segment's target, and never under a planned 250-word segment's worth. Uncapped, Qwen3 1.7B looped on a 225-word segment until its 40,960-token window was full, and the JSON retry, which replays the failed reply, could not fit. The target is the outline's own guess: Qwen3 1.7B once gave a segment 20 words, wrote past them, and a 240-token cap ended both replies mid-JSON. The chosen audio model voices every line through audio.cpp's server, and the transcript is the body.
 - **image**: the model writes a title and an image prompt, and the image model paints the prompt.
diff --git a/docs/proposals/agent/01-which-engine.md b/docs/proposals/agent/01-which-engine.md
index 1f225b042b..9036686702 100644
--- a/docs/proposals/agent/01-which-engine.md
+++ b/docs/proposals/agent/01-which-engine.md
@@ -13,7 +13,7 @@
 
 - Any GGUF model can be held to a JSON schema. At `b11050`, a request with `response_format` gets a grammar that allows the model's reasoning block first, then the JSON, optionally inside a `json` code fence ([`common/chat-auto-parser-generator.cpp`](https://github.com/ggml-org/llama.cpp/blob/b11050/common/chat-auto-parser-generator.cpp)).
 - In the same file, a request with both `response_format` and `tools` gets the schema parser and no tool-call parsing. A request uses one or the other.
-- Both chat providers accept a `json_schema`, and no caller passes one yet ([selection](../../architecture/local-models/selection.md), Known gaps).
+- Both chat providers accept a `json_schema`, and only Studio's quiz passes one yet ([selection](../../architecture/local-models/selection.md), Known gaps).
 
 ## Tool support for remote models
 
diff --git a/surfsense_local/backend/modules/llm/providers/protocols.py b/surfsense_local/backend/modules/llm/providers/protocols.py
index ae572f61eb..a28a704a98 100644
--- a/surfsense_local/backend/modules/llm/providers/protocols.py
+++ b/surfsense_local/backend/modules/llm/providers/protocols.py
@@ -41,6 +41,7 @@ def chat(
         max_tokens: int | None = None,
         temperature: float | None = None,
         reasoning: bool | None = None,
+        json_schema: dict | None = None,
     ) -> AsyncIterator[str]:
         """The answer text alone; a thinking model's trace is left out."""
         ...
@@ -53,6 +54,7 @@ def chat_deltas(
         max_tokens: int | None = None,
         temperature: float | None = None,
         reasoning: bool | None = None,
+        json_schema: dict | None = None,
     ) -> AsyncIterator[Delta]:
         """The reply as it streams, with the trace marked apart from the answer."""
         ...
diff --git a/surfsense_local/backend/tests/unit/worker/test_studio_content.py b/surfsense_local/backend/tests/unit/worker/test_studio_content.py
index 3d03e2fd52..80d55cc4ec 100644
--- a/surfsense_local/backend/tests/unit/worker/test_studio_content.py
+++ b/surfsense_local/backend/tests/unit/worker/test_studio_content.py
@@ -1,6 +1,7 @@
 """Content kinds: the model writes markdown or JSON, the worker renders it as-is."""
 
 import json
+from types import SimpleNamespace
 
 import pytest
 
@@ -8,7 +9,9 @@
 from worker.studio.content.flashcards import pipeline as flashcards
 from worker.studio.content.mindmap import pipeline as mindmap
 from worker.studio.content.quiz import pipeline as quiz
+from worker.studio.content.quiz import schema as quiz_schema
 from worker.studio.content.summary import pipeline as summary
+from worker.studio.shared import generate
 from worker.studio.shared.text import parse_json
 
 pytestmark = pytest.mark.unit
@@ -49,6 +52,33 @@ def test_a_quiz_is_capped_where_its_prompt_says_it_is() -> None:
     assert len(json.loads(built.primary)["questions"]) == quiz.QUESTIONS
 
 
+def test_a_quiz_asks_the_model_for_its_schema(monkeypatch: pytest.MonkeyPatch) -> None:
+    """The shape the builder reads is enforced while the model writes, so a
+    small model cannot drift off it; the prompt still says it in prose."""
+    sent: list[dict | None] = []
+
+    def fake_run_model(*_args: object, json_schema: dict | None = None, **_kw: object):
+        sent.append(json_schema)
+        return '{"title": "T", "questions": []}'
+
+    monkeypatch.setattr(generate, "run_model", fake_run_model)
+    model = SimpleNamespace(tier=Tier.COMPACT)
+
+    quiz.render(model, [], None)
+
+    assert sent == [quiz_schema.REPLY]
+
+
+def test_the_quiz_schema_asks_for_what_the_builder_keeps() -> None:
+    """A question the builder would drop is one the grammar should not allow."""
+    question = quiz_schema.REPLY["properties"]["questions"]["items"]
+    options = question["properties"]["options"]
+
+    assert set(quiz_schema.REPLY["required"]) == {"title", "questions"}
+    assert set(question["required"]) == {"question", "options", "answer", "explanation"}
+    assert options["minItems"] == options["maxItems"] == quiz.OPTIONS
+
+
 def test_every_content_kind_is_asked_for_in_its_own_words_at_every_tier() -> None:
     """One prompt per kind and tier: a wording that suits a quiz never reaches a deck."""
     asked = {
diff --git a/surfsense_local/backend/tests/unit/worker/test_studio_generate.py b/surfsense_local/backend/tests/unit/worker/test_studio_generate.py
index 61dc99c305..acf50f6a83 100644
--- a/surfsense_local/backend/tests/unit/worker/test_studio_generate.py
+++ b/surfsense_local/backend/tests/unit/worker/test_studio_generate.py
@@ -42,6 +42,29 @@ def test_a_cap_reaches_llama_server() -> None:
     assert fake.chat_bodies[-1]["max_tokens"] == 1200
 
 
+def test_a_schema_reaches_llama_server() -> None:
+    """A format that asks for JSON gets a grammar, not only a request in prose."""
+    fake = FakeRouter(["qwen3"])
+    provider = LlamaCppProvider("http://127.0.0.1:1234", transport=fake.transport())
+    schema = {"type": "object", "properties": {"title": {"type": "string"}}}
+
+    generate.run_model(
+        ResolvedGeneration(SELECTION, provider), "system", [], json_schema=schema
+    )
+
+    assert fake.chat_bodies[-1]["response_format"]["json_schema"]["schema"] == schema
+
+
+def test_a_format_that_asks_for_no_schema_sends_none() -> None:
+    """Office writes Python and the summary writes markdown; neither is JSON."""
+    fake = FakeRouter(["qwen3"])
+    provider = LlamaCppProvider("http://127.0.0.1:1234", transport=fake.transport())
+
+    generate.run_model(ResolvedGeneration(SELECTION, provider), "system", [])
+
+    assert "response_format" not in fake.chat_bodies[-1]
+
+
 class _ModelThatNeverFinishes:
     """Streams forever, or reads its prompt forever, until the caller hangs up."""
 
diff --git a/surfsense_local/backend/worker/studio/content/quiz/pipeline.py b/surfsense_local/backend/worker/studio/content/quiz/pipeline.py
index 30087dbceb..857e9ff928 100644
--- a/surfsense_local/backend/worker/studio/content/quiz/pipeline.py
+++ b/surfsense_local/backend/worker/studio/content/quiz/pipeline.py
@@ -3,11 +3,11 @@
 from modules.llm import prompting
 from modules.llm.profile import Tier
 from modules.llm.resolution import ResolvedGeneration
+from worker.studio.content.quiz.schema import OPTIONS, REPLY
 from worker.studio.shared import generate
 from worker.studio.shared.artifact import Built, Source
 from worker.studio.shared.text import as_list, as_text, parse_json, slug
 
-OPTIONS = 4
 # The frontier prompt leaves the count to the material, so the ceiling is kept here.
 QUESTIONS = 10
 
@@ -15,9 +15,10 @@
 def render(
     model: ResolvedGeneration, sources: list[Source], user_prompt: str | None
 ) -> Built:
-    return build(
-        generate.run_model(model, prompt(model.tier, user_prompt), sources), sources
+    raw = generate.run_model(
+        model, prompt(model.tier, user_prompt), sources, json_schema=REPLY
     )
+    return build(raw, sources)
 
 
 def prompt(tier: Tier, user_prompt: str | None) -> str:
diff --git a/surfsense_local/backend/worker/studio/content/quiz/schema.py b/surfsense_local/backend/worker/studio/content/quiz/schema.py
new file mode 100644
index 0000000000..e96cbecbdd
--- /dev/null
+++ b/surfsense_local/backend/worker/studio/content/quiz/schema.py
@@ -0,0 +1,36 @@
+"""The quiz reply's shape, enforced as a grammar while the model writes.
+
+Flat and plain on purpose: only types, `required` and array bounds, which
+llama.cpp's json-schema-to-grammar turns into a bounded repetition at b11050.
+That an answer is one of its options cannot be said here; the builder still
+checks it.
+"""
+
+# The prompts ask for exactly this many; the builder drops any other count.
+OPTIONS = 4
+
+REPLY = {
+    "type": "object",
+    "properties": {
+        "title": {"type": "string"},
+        "questions": {
+            "type": "array",
+            "items": {
+                "type": "object",
+                "properties": {
+                    "question": {"type": "string"},
+                    "options": {
+                        "type": "array",
+                        "items": {"type": "string"},
+                        "minItems": OPTIONS,
+                        "maxItems": OPTIONS,
+                    },
+                    "answer": {"type": "string"},
+                    "explanation": {"type": "string"},
+                },
+                "required": ["question", "options", "answer", "explanation"],
+            },
+        },
+    },
+    "required": ["title", "questions"],
+}
diff --git a/surfsense_local/backend/worker/studio/shared/generate.py b/surfsense_local/backend/worker/studio/shared/generate.py
index 9160017b56..b2d6841f1d 100644
--- a/surfsense_local/backend/worker/studio/shared/generate.py
+++ b/surfsense_local/backend/worker/studio/shared/generate.py
@@ -31,6 +31,7 @@ def run_model(
     *,
     repair: Repair | None = None,
     max_tokens: int | None = None,
+    json_schema: dict | None = None,
 ) -> str:
     """Send one system prompt plus the grounding to the chosen generation model.
 
@@ -40,6 +41,9 @@ def run_model(
     A retry passes `repair`, which replays the failed reply as the model's own
     turn before asking for the correction. Without it an error naming a line
     points at a script the model was never shown, so it can only start over.
+
+    A JSON format passes `json_schema`, which the runtime turns into a grammar.
+    An endpoint that ignores it still answers, and `parse_json` reads that.
     """
     selected = model.selection
     messages = [
@@ -64,7 +68,11 @@ def run_model(
     reply = asyncio.run(
         _collect(
             model.generator.chat(
-                selected.name, messages, max_tokens=max_tokens, reasoning=False
+                selected.name,
+                messages,
+                max_tokens=max_tokens,
+                reasoning=False,
+                json_schema=json_schema,
             )
         )
     )