---
description: Constants and shared elements synchronization between backend and frontend
alwaysApply: false
---
# Backend-to-Frontend Synchronization

The backend is the source of truth. Frontend types and constants are generated/validated from backend definitions.

## Two Mechanisms

1. **OpenAPI → TypeScript**: API response types are generated from FastAPI's OpenAPI schema using `openapi-typescript`. Regenerate with `make generate-types-standalone` after changing Pydantic schemas.

2. **Shared Constants**: `shared/constants.json` holds values needed by both sides (roles, statuses, validation rules). Backend validates this file matches its definitions at startup.

## Key Principle

Never manually define types or constants in the frontend that originate from the backend. Import from `generated/api.ts` or `shared/constants.json` instead.

See `Makefile` for sync commands (`generate-types-standalone`, `check-types-fresh`, `check-constants`).