All termsENGINEERING & ARCHITECTURE

API

Application Programming Interface

Also known as: Application Programming Interface

DEFINITION

A defined interface for one piece of software to communicate with another — the contract between client and server.

In depth

Most modern SaaS products expose at least one API: internal (between your frontend and backend) and often external (for integrations and automation). External APIs are products in themselves — they need pricing, versioning, documentation, and SLAs.

Best-in-class API design today means REST + OpenAPI for CRUD, plus webhooks for server-pushed events. GraphQL is strong when the client shape varies a lot. gRPC is for internal service-to-service.

Put it into practice

feature

API reference generator

Related terms

Webhooks

Server-to-server HTTP callbacks fired when a specific event happens — the push counterpart to pull APIs.

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Last reviewed 14 April 2026 by Abhi Verma.