Johnny UnarUI-first is a trap
Most teams build the UI first and figure out the API later. It works — until it doesn't. You end up with endpoints shaped around specific screens, data structures that don't make sense outside the original context, and an API that's impossible to reuse for mobile apps, third-party integrations, or internal tools. API-first flips this: design the contract first, then build everything on top of it.
Compounding benefits
The benefits compound over time. When your API is well-designed from the start, frontend and backend teams can work in parallel — the frontend mocks the API while the backend implements it. New clients (mobile apps, partner integrations, internal dashboards) plug in without backend changes. Your documentation stays accurate because it's generated from the same spec that drives development.
OpenAPI as the standard
OpenAPI (Swagger) is the industry standard for REST APIs. Define your endpoints, request/response schemas, and authentication in a YAML or JSON file. Tools like Stoplight or Redocly provide visual editors. For type safety, generate TypeScript types directly from your OpenAPI spec — libraries like openapi-typescript make this seamless. For GraphQL projects, the schema itself serves as the contract.
Keep it practical
API-first doesn't mean over-engineering. Start with the resources your product actually needs. Version from day one (even if you only have v1). Use consistent naming conventions and HTTP status codes. Add rate limiting and authentication before you go public. And document everything — not because it's nice to have, but because your future self (and your integration partners) will thank you.
