APIkontrakter

APIkontrakter (API contracts) are a formal agreement between an API provider and its consumers that specifies the expected behavior of the API. They cover what endpoints and operations are available, the request and response data formats, authentication requirements, and error handling. They also outline non-functional constraints such as rate limits and availability targets. By codifying these expectations, the contract serves as a single source of truth to guide design, implementation, integration, and testing, and to manage changes over time.

Core components typically include: endpoints and HTTP methods; request and response schemas; data types and field constraints; authentication and authorization; error codes and messages; header requirements; and rules for pagination, filtering, and sorting. Contracts are often written in machine-readable formats to enable automation, client code generation, and contract testing.

Two common approaches are contract-first design, where the contract is defined before implementation, and code-first design, where the contract is inferred from a running API. Popular specifications include OpenAPI, AsyncAPI, RAML, and API Blueprint. These formats enable tooling for validation, mocking, and automated tests, as well as API discovery and governance.

Contract testing verifies compatibility between provider and consumer as the API evolves. Techniques such as consumer-driven contracts and tools like Pact support end-to-end testing across services. Versioning and deprecation policies are typically part of the contract to manage backward compatibility and planned migrations. Security, privacy, and data-sharing constraints are also documented in the contract.

Overall, API contracts function as living documents that evolve with API ecosystems. They support collaboration, reliable integration, and reduced runtime failures by aligning producer and consumer expectations.