# Yannis JSON errors

JSON API errors on yannis.dev use RFC 9457 problem details with Content-Type: application/problem+json. The core fields are type, title, status, detail, and instance. Yannis also returns code and hint extension fields so agents can branch on a stable machine value and show a practical recovery step without parsing prose.

Problem type URLs live on this page. The current public codes are api.not_found for unknown API routes, http.method_not_allowed when a method is not supported, http.forbidden_origin when an MCP Origin header is not http or https, http.not_acceptable when a requested media type cannot be produced, request.invalid_json when a body cannot be parsed, mcp.unsupported_protocol_version for unsupported MCP protocol headers, rate_limit.exceeded for 429 responses, and server.error for unexpected failures.

A typical response is a JSON object such as {"type":"https://yannis.dev/developers/errors#api.not_found","title":"API route not found","status":404,"detail":"The requested API path is not published on yannis.dev.","instance":"/api/example","code":"api.not_found","hint":"Read https://yannis.dev/openapi.json and retry a documented path."}

HTML pages still return HTML for browsers. API paths and machine-readable resources return structured JSON errors where the site controls the response. If an intermediary or static host produces an error before this code runs, check [/openapi.json](/openapi.json) for the canonical endpoint list and email [hello@yannis.dev](mailto:hello@yannis.dev) with the failing URL.

## Links

- [Home](https://yannis.dev/)
- [Developer resources](https://yannis.dev/developers)
- [OpenAPI](https://yannis.dev/openapi.json)
- [MCP server](https://yannis.dev/mcp)
- [llms.txt](https://yannis.dev/llms.txt)
- [Contact](https://yannis.dev/contact)