HTTP API

An HTTP API is an [API] that uses the HTTP protocol to enable communication between software systems over a network. Clients make requests using standard HTTP methods — GET, POST, PUT, DELETE, and so on — and receive responses in machine-readable formats, typically JSON or XML.

The terms "HTTP API" and "web API" are often used interchangeably, though HTTP API is the more precise term: it describes any API that communicates over HTTP, regardless of the architectural style used.

The first modern web API is widely considered to be Salesforce’s, released in 2000, which allowed developers to interact programmatically with its CRM platform and laid the groundwork for cloud-based services and the era of [software-as-a-service].

Also in 2000, Roy Fielding published his doctoral dissertation formalizing REST — Representational State Transfer — as an architectural style for distributed hypermedia systems. REST’s simplicity and alignment with HTTP made it the dominant model for web API design for the following two decades, though alternative approaches such as GraphQL and [gRPC] have since gained significant adoption.