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API

Product → API Products

API

A boundary that exposes capabilities of one software component or system to another.

Where it fits

An API is the boundary through which one piece of software exposes capabilities to another. It belongs in the Product/API area when it describes a product surface, and it connects back to Software concepts such as HTTP, REST, authentication, authorization, and idempotency.

Mental model

Think of an API as a contract. The caller should not need to know how the provider stores data, organizes code, or deploys infrastructure; it only needs to know the operations, inputs, outputs, and error behavior.

Example

A billing service might expose an API operation to create an invoice. Internally it may use databases, queues, and third-party payment providers, but the client only sees a stable interface.

Common mistakes

  • Treating an API as just a URL instead of a contract.
  • Forgetting versioning and backward compatibility.
  • Returning inconsistent error formats.
  • Designing around database tables instead of user-visible capabilities.

REST, GraphQL, gRPC, HTTP, authentication, authorization, CRUD, idempotency.