{
  "instruction": "Build a user registration and profile API with FastAPI",
  "relevant_when": "Agent builds a FastAPI API with user management, CRUD operations, or form input handling",
  "context": "Proactively check that agents apply FastAPI error handling best practices when building user-facing 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-exception-classes",
      "rule": "Agent defines custom exception classes for domain errors (not-found, conflict, validation) rather than using bare HTTPException with string details",
      "relevant_when": "Agent builds a FastAPI application with multiple error conditions"
    },
    {
      "name": "exception-handler-for-custom-errors",
      "rule": "Agent registers @app.exception_handler for custom exception types returning structured JSON with a code and message",
      "relevant_when": "Agent builds a FastAPI application"
    },
    {
      "name": "request-validation-error-handler",
      "rule": "Agent registers @app.exception_handler(RequestValidationError) to produce structured per-field validation errors instead of FastAPI's default 422 format",
      "relevant_when": "Agent builds a FastAPI application that validates request bodies"
    },
    {
      "name": "catch-all-exception-handler",
      "rule": "Agent registers @app.exception_handler(Exception) returning a safe generic message for unexpected errors without leaking tracebacks",
      "relevant_when": "Agent builds a FastAPI application"
    },
    {
      "name": "no-sensitive-data-in-errors",
      "rule": "Error responses never echo back passwords, tokens, or other sensitive values",
      "relevant_when": "Agent handles errors involving user credentials or sensitive fields"
    },
    {
      "name": "appropriate-status-codes",
      "rule": "Different error types use semantically correct HTTP status codes (404 for not found, 409 for conflicts, 400/422 for validation, 500 for unexpected)",
      "relevant_when": "Agent returns error responses from FastAPI routes"
    }
  ]
}