oai/openapi-specification

The OpenAPI Specification is a community-maintained standard that defines how to describe HTTP APIs, the interfaces that let software systems talk to each other over the internet, in a structured, machine-readable format. Think of it as a universal blueprint language for APIs: instead of reading through scattered documentation or guessing how to call a service, developers write (or generate) one document in either YAML or JSON format that describes exactly what endpoints exist, what data they accept, and what they return. This solves a very common problem in software development: when you want to connect to someone else's service (say, a payment provider or weather service), you normally have to dig through their docs, experiment with requests, and write custom client code by hand. With an OpenAPI document in place, tools can automatically generate that code for you, produce interactive documentation that you can click through in a browser, or build automated tests, all from the same source of truth. You would use this when building or consuming a web API and you want to save time, reduce miscommunication between teams, or unlock automated tooling. It is particularly useful when a frontend team needs to work against a backend that is still being built: the OpenAPI document serves as a contract both sides agree on upfront. The specification itself is just a written standard, this repository is written in Markdown and represents the document defining what a valid OpenAPI description looks like, not software you install or run. It is maintained by the OpenAPI Initiative, a Linux Foundation project, with community input.