SchemaFit
CI linter for LLM structured-output schemas
SchemaFit launched on June 29, 2026 with 9 votes, #1,453 of 22,647 launches that month and more than 90% of that year's launches.
What it does
SchemaFit is an MIT-licensed CI linter for LLM structured-output schemas. It checks JSON Schema, tool definitions, and response_format schemas against provider-specific constraints before runtime. It catches unsupported keywords, nesting issues, required/optional mismatches, and portability problems across OpenAI, Anthropic, Gemini, Mistral, and Cohere, so teams can fail PRs instead of production calls.
schemafit is a local-first, MIT-licensed CLI that lints a JSON Schema, structured-output spec, or tool definition against each provider
Lint your LLM structured-output & JSON schemas against OpenAI, Anthropic, Gemini, Mistral, and Cohere — and fail CI before they 400 in production. Open source (MIT) · Static & offline · Zero runtime dependencies · CI-enforceable. A JSON Schema / tool definition / response_format that works on OpenAI can 400 on Anthropic or Gemini (and vice-versa): nested oneOf, a missing additionalProperties: false, a default in a property, Anthropic-rejected keywords (minLength, format, pattern), Gemini’s lack of anyOf. The API tells you it failed — not which constraint — so teams hand-port schemas and debug by trial-and-error at runtime. schemafit encodes each provider’s documented constraint surface as a…from danmercede.com
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