API, explained
An API specifies what you can ask for, how to ask (endpoints, methods, parameters, authentication) and what you get back. The caller depends only on that contract, so the provider can change its internals freely, as long as the contract holds.
Most APIs on the web are HTTP APIs, commonly following REST conventions, GraphQL, or gRPC. Companies increasingly build products by composing other companies’ APIs for payments, messaging, identity, maps and AI, which is why changes to those contracts ripple so widely.
When a provider changes the contract in a way existing callers cannot absorb, that is a breaking change.
Related terms
- REST API: A REST API is an HTTP API organised around resources identified by URLs and manipulated with standard methods such as GET, POST, PUT, PATCH and DELETE.
- OpenAPI Specification: The OpenAPI Specification is a standard, language-agnostic format (YAML or JSON) for describing HTTP APIs: their paths, operations, parameters, schemas and authentication.
- Breaking change: A breaking change is a change to an API that causes a correctly written client, which worked before, to fail or behave differently without modifying its code.