Full-Stack Development

Use for features that span both FastAPI backend and Next.js frontend.

Architecture

• Backend: FastAPI + Python 3.13+, TinyDB, LiteLLM
• Frontend: Next.js 16 + React 19, Tailwind CSS v4, Swiss International Style
• API: REST endpoints at /api/v1/*

Workflow

1. Design the API contract first

Route:     POST /api/v1/my-feature
Request:   { field: string, ... }
Response:  { id: string, result: ... }

2. Backend implementation

• Schema in apps/backend/app/schemas/
• Service in apps/backend/app/services/
• Router in apps/backend/app/routers/
• Register router in apps/backend/app/main.py

3. Frontend implementation

• API call in apps/frontend/lib/
• Component in apps/frontend/components/
• Page integration in apps/frontend/app/

4. Verify end-to-end

• Backend serves correct data
• Frontend displays correctly with Swiss style
• Error states handled on both sides

Non-Negotiable Rules

Backend

• Type hints on all functions
• copy.deepcopy() for mutable defaults
• Log errors server-side, generic messages to clients
• API keys via api_key= parameter

Frontend

• Swiss International Style (rounded-none, hard shadows, Swiss palette)
• npm run lint && npm run format
• Enter key handling on textareas
• Promise.all() for independent fetches

Key Files

References

• API contracts: docs/agent/apis/front-end-apis.md
• Backend guide: docs/agent/architecture/backend-guide.md
• Frontend workflow: docs/agent/architecture/frontend-workflow.md
• Style guide: docs/agent/design/style-guide.md