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# Interactive API documentation
Introduces the interactive documentation tool for the GitLab API.
## About the OpenAPI specification
The [OpenAPI specification](https://swagger.io/specification/) (formerly called Swagger) defines a standard, language-agnostic interface to RESTful APIs. OpenAPI definition files are written in the YAML format, which is automatically rendered by the GitLab browser into a more human-readable interface. For general information about the GitLab APIs, see [API Docs](../README.md).
## Overview
The [interactive API documentation tool](openapi.yaml) allows API testing directly on the GitLab.com
website. Only a few of the available endpoints are documented with the OpenAPI spec, but the current
list demonstrates the functionality of the tool.
![API viewer screenshot](img/apiviewer01-fs8.png)
## Endpoint parameters
When you expand an endpoint listing, you'll see a description, input parameters (if required),
and example server responses. Some parameters include a default or a list of allowed values.