What Is API-First Development?
API-first development means designing and building the API before the user interface — treating the API as the core product that web, mobile, and third-party clients consume.
In API-first development, the API contract is defined before any frontend code is written. The backend team ships endpoints. The web team and the mobile team both consume the same API independently.
Why API-first wins for multi-platform products: If you build your web app and your API as one tightly coupled thing, adding a mobile app later means untangling business logic from the UI layer. API-first separates concerns from day one — your Flutter app and your Next.js app call the same REST or GraphQL endpoints.
What API-first looks like in practice:
- Document the API spec (OpenAPI / Swagger) before writing handlers
- Backend ships endpoints with mock data; frontend builds against the spec in parallel
- API is versioned so clients aren't broken by changes
- Authentication is standardized across all clients (JWT, API keys)
API-first vs. API-later: Most MVPs start with a coupled web app. API-first adds upfront planning overhead — worth it if you're certain you'll need mobile or third-party integrations. If you're validating a hypothesis, ship the coupled version first and extract the API when you have evidence you need it.
Tools that support API-first: Supabase auto-generates a REST API and a type-safe client from your Postgres schema. Next.js API routes can serve both web and mobile clients from the same codebase.