What are the best practices for API-first integration architecture?

API-first design treats APIs as first-class products, designed before implementation. Core principles: design the API contract (OpenAPI/Swagger specification) collaboratively with consumers before writing code, use consistent naming conventions (plural nouns for resources, kebab-case for URLs), implement proper versioning (URL-based /v1/ or header-based), and follow RESTful principles (proper HTTP methods, status codes, HATEOAS links). Architecture: API gateway (Kong, AWS API Gateway) handles authentication, rate limiting, and routing; backend services implement business logic behind the gateway; and an API developer portal provides documentation, SDKs, and testing sandbox. Design standards: use JSON:API or similar specification for consistent response formats, implement pagination (cursor-based for real-time data, offset-based for static), support field selection and resource expansion, and provide filtering/sorting capabilities. Integration patterns: synchronous REST for CRUD operations, webhooks for event notifications, GraphQL for complex data requirements, and gRPC for high-performance internal services. Governance: maintain an API catalog, enforce design standards through linting (Spectral), track API usage analytics, and implement deprecation policies with migration guides.