FastAPI Scaffolder

"An API is a contract — make it explicit, versioned, and documented. Security by default means the insecure path requires more work than the secure path."

Core Philosophy

FastAPI has OpenAPI documentation built in — but built-in is not automatic. Every endpoint needs explicit metadata (summary, description, response_model, responses) to produce docs useful to consumers; an endpoint without metadata is a black box. Security by default means every router requires authentication unless an endpoint explicitly, intentionally opts out — an unauthenticated endpoint is a deliberate decision, not an oversight.

Non-Negotiable Constraints:

1. OPENAPI-FIRST — every endpoint has summary, description, response_model, and a responses dict.
2. VERSIONING FROM DAY ONE — /api/v1/ prefix via APIRouter(prefix="/api/v1"); changing it later is breaking.
3. SECURITY BY DEFAULT — Depends(get_current_user) at router level; anonymous access is an explicit opt-out.
4. PYDANTIC V2 MODELS — all request/response types are BaseModel subclasses; no bare dict/Any returns.
5. TYPED RESPONSES — explicit response_model= on every route; no implicit response inference.

Full principle table, KB lookups, discipline rules, anti-patterns, and error recovery live in references/conventions.md.

Workflow

DETECT     Find the app entry point (main.py/app.py); check existing versioning, auth
           (get_current_user/OAuth2/HTTPBearer), and middleware (CORS) via grep.

CONFIGURE  Project-level setup: app creation, config (pydantic-settings), shared dependencies,
           exception handlers, CORS, health. (Structure in output-templates.md.)

SCAFFOLD   Create the endpoint with full OpenAPI metadata, Pydantic v2 request/response models, and
           security. (Complete scaffold in references/router-template.md.)

SECURE     Add authentication, authorization (role factories), and rate limiting (stricter on auth
           endpoints). (JWT + API-key patterns in references/security-patterns.md.)

DOCUMENT   uvicorn up; verify /openapi.json and /docs render the new endpoints with metadata.

VERIFY     App starts; /health passes; /docs renders; pytest passes; ruff check; mypy app/.

Exit criteria: router registered under /api/v1 with router-level auth; every route has response_model, summary, and a responses dict; rate limiting applied (strict on auth); health endpoints present; app starts, /docs renders, tests/ruff/mypy pass.

State Block

<fastapi-scaffold-state>
phase: DETECT | CONFIGURE | SCAFFOLD | SECURE | DOCUMENT | VERIFY | COMPLETE
project_structure: new | existing
versioning_configured: true | false
auth_configured: true | false
cors_configured: true | false
rate_limiting_configured: true | false
health_checks_added: true | false
openapi_complete: true | false
last_action: [description]
next_action: [description]
</fastapi-scaffold-state>

Output Template

• Endpoint scaffold checklist, project structure — references/output-templates.md.
• Complete endpoint scaffold (router, models, OpenAPI metadata) — references/router-template.md.
• JWT authentication, API key, role factory, rate limiting patterns — references/security-patterns.md.
• Principle table, KB lookups, discipline rules, anti-patterns, error recovery — references/conventions.md.

Integration with Other Skills