OpenAPI is a standard way to describe a web API in one document, listing its endpoints, inputs and outputs, so people and programs can understand and call it.
In plain words
To use a web API you need to know its addresses, what to send and what comes back. The OpenAPI Specification puts all of that in a single document written in JSON or YAML, in a form that does not depend on any programming language. Humans can read it, and tools can use it to generate client code, developer portals and test cases.
A quick example
Imagine a weather service with an endpoint that takes a city and returns a forecast. Its OpenAPI document spells out the path, the city parameter and the shape of the reply. A developer, or a program reading the document, can then call the service correctly without seeing its source code.
Where you'll meet it
- Documenting and designing web APIs.
- Generating client code and API tests.
Related
Sources
- DocsOpenAPI Specification, OpenAPI Initiative · read 29 Sept 2026
- DocsWhat is OpenAPI?, OpenAPI Initiative · read 29 Sept 2026
Checked by WhatIsAI against the sources above · 29 Sept 2026. Spotted an error? Report it.