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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.
## 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.
## Starting an interactive sesssion
A [Personal access token](../../user/profile/personal_access_tokens.md)(PAT) is one way to
start an interactive session. To do this, select **Authorize** from the main page, and a
dialog box prompts you to enter your PAT, which is valid for the current web session.
To test the endpoint, first select **Try it out** on the endpoint definition page. Input the parameters
as required, then select **Execute**. In the following example, we executed a request for the `version`
endpoint (no parameters required). The tool shows the `curl` command and URL of the request, followed
by the server responses that are returned. You can create new responses by editing the relevant parameters
