{
  "instruction": "Build an order management API with FastAPI",
  "relevant_when": "Agent builds a FastAPI API with state machines, order processing, or complex business rules",
  "context": "Proactively check that agents apply FastAPI error handling best practices when building order/workflow APIs, even when not explicitly asked to add error handling.",
  "sources": [
    {
      "type": "file",
      "filename": "skills/fastapi-error-handling/SKILL.md",
      "tile": "tessl-labs/fastapi-error-handling"
    }
  ],
  "checklist": [
    {
      "name": "custom-exceptions",
      "rule": "Agent defines custom exception classes for domain errors (NotFoundError, InvalidStateTransition, etc.) rather than using bare HTTPException everywhere",
      "relevant_when": "Agent builds a FastAPI application with business logic errors"
    },
    {
      "name": "exception-handler-registered",
      "rule": "Agent registers @app.exception_handler for custom exception types returning structured JSON with code and message",
      "relevant_when": "Agent builds a FastAPI application"
    },
    {
      "name": "validation-error-handler",
      "rule": "Agent registers @app.exception_handler(RequestValidationError) with per-field error details in a consistent format",
      "relevant_when": "Agent builds a FastAPI app accepting request bodies"
    },
    {
      "name": "generic-catch-all",
      "rule": "Agent registers @app.exception_handler(Exception) returning a safe generic error message without leaking internal details",
      "relevant_when": "Agent builds a FastAPI application"
    },
    {
      "name": "consistent-error-shape",
      "rule": "All error responses (validation, not-found, business rule violations, state transition errors) use the same JSON structure with a code and message",
      "relevant_when": "Agent returns error responses from FastAPI routes"
    },
    {
      "name": "correct-status-codes",
      "rule": "Different error types use semantically correct HTTP status codes (404, 409, 400/422, 500) not all mapped to the same code",
      "relevant_when": "Agent returns error responses from FastAPI"
    }
  ]
}