A REST API is an application programming interface (Application Programming Interface) that lets two software applications communicate with each other through the HTTP protocol — the very one that powers the Web. REST (Representational State Transfer) is an architectural style described by Roy Fielding in 2000; it relies on existing Web standards rather than a proprietary protocol, which makes it simple to adopt and broadly interoperable.
In a REST API, each piece of data is exposed as a resource identified by a URL (for example /clients/123). You act on these resources with the standard HTTP verbs: GET to read, POST to create, PUT or PATCH to update, DELETE to remove. Exchanges most often travel in JSON format, which is lightweight, human-readable and easy for machines to process.
REST is stateless (session-less): each request carries all the information needed to process it, notably the authentication token, without the server having to remember the context of previous exchanges. Responses come with an HTTP status code (200 success, 201 created, 401 unauthorized, 404 not found…). This simplicity is why REST has become the de facto standard for integrations between applications.
eyeot exposes a REST API documented to the OpenAPI specification and secured with tokens. It is the foundation of the integrations module and of connecting third-party tools; application authorization relies in particular on OAuth 2.1.