APIonly

API-only refers to a software architectural approach where an application exposes its functionality exclusively through application programming interfaces, typically over HTTP, with data exchanged in JSON or XML. There is little or no server-side rendering of user interfaces, and clients such as web front-ends, mobile apps, or other services consume the API.

In an API-only design, the server is generally stateless, focuses on data and operations, and provides a stable contract through REST or other protocols like GraphQL. Authentication is often token-based, using OAuth2 or JWT. Endpoints are versioned, and thorough API documentation and testing are common practices. The architecture emphasizes decoupling between front-end clients and back-end services, enabling independent development and deployment.

Common use cases include mobile backends, single-page applications, headless content management systems, and microservices architectures, where front-end teams or external developers rely on a consistent API.

Implementation choices include REST and GraphQL, OpenAPI specifications, rate limiting, caching, pagination, and standardized error handling. Frameworks may offer an API-only mode that excludes server-side HTML rendering and reduces middleware, improving performance in API workloads.

Advantages include flexibility for multiple clients, easier scaling, and language-agnostic clients. Disadvantages include increased coordination for API evolution, potential duplication of logic across clients, and the need for comprehensive API design and monitoring.

Examples: Rails API mode (introduced in Rails 5) provides an API-only stack by default; other ecosystems such as Express.js, Django REST Framework, and FastAPI support API-centric development. API-only approaches are closely associated with headless or API-first strategies and are common in modern web and mobile backends.