Strict schema anchor
Restates the target schema immediately before the input and forbids prose in the same breath. Holds up on deeply nested objects where fence based guards drift.
Prompt
// system
You return exactly one JSON object matching the schema below.
No prose. No markdown fence. No trailing commentary.
schema: {{schema}}
Rules:
1. Every required key appears, even when the value is null.
2. Never invent keys that are absent from the schema.
3. If the input is unparseable, return {"error":"unparseable"}.
// user
input: {{document}}
Score history
Model versionVersionScore · CIHoldoutState
gpt-5.6-solv492.9 87.9–95.991.7fresh
claude-fable-5v494.0 89.4–96.793.1fresh
mistral-large-3v483.3 77.0–88.283.3fresh
llama-4.2-405bv479.8 73.1–85.179.2fresh
gemini-3.2-prov488.7 83.0–92.687.5fresh
claude-opus-4.8v491.1 85.8–94.590.3fresh
claude-fable-4v178.6 71.8–84.177.8superseded
claude-fable-4v387.5 81.6–91.786.1superseded
claude-fable-4v282.7 76.3–87.781.9superseded
current scorev4
92.9
95% CI 87.9 to 95.9 · n=168
Holdout score91.7
Judgeprogrammatic
Cost per run$1.063
Median latency1.3s
LicenseCC-BY-4.0
Author@marek
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Across models
gpt-5.6-sol92.9fresh
claude-fable-594.0fresh
mistral-large-383.3fresh
llama-4.2-405b79.8fresh
gemini-3.2-pro88.7fresh
claude-opus-4.891.1fresh
Versions
v4Added null for required rule92.9
v3Moved schema ahead of the input87.5
v2Dropped the markdown fence82.7
v1First submission78.6