API Development Conventions

These conventions apply when working on the API layer (routes, MCP tools, CLI commands).

Authentication

• All endpoints require valid authentication (Bearer token, session cookie, or API key)
• Use dependency injection for auth (e.g., Depends(get_current_user) in FastAPI)
• Provide both required and optional auth dependencies where appropriate
• Rate limit registration and auth endpoints to prevent brute-force
• Resource ownership is enforced -- users can only access their own resources

Route Organization

• One route file per resource domain: routes_users.py, routes_orders.py, etc.
• Each route file defines a router (e.g., APIRouter in FastAPI)
• Routers are registered in the main app file

Error Responses

• 422 -- Validation errors (malformed input)
• 404 -- Resource not found
• 429 -- Rate limits (pass through from upstream with reset timing)
• 503 -- Upstream service unavailability
• Error messages must be specific and actionable, not generic

Resource Ownership

• Every endpoint that accesses a user's resource must verify ownership
• Use the dependency injection pattern for ownership checks
• Never allow cross-user resource access

MCP Server (if applicable)

• Tools mirror REST API functionality
• Each tool has a clear description to help LLMs understand when to use it
• Include example parameter values in descriptions
• Return strings for LLM consumption

CLI (if applicable)

• Commands organized by resource domain
• Consistent flag naming across commands
• Help text on every command and argument

Middleware

• Security middleware for headers, CORS, CSP
• Rate limiting middleware
• All middleware must be async (if using async framework)