API documentation

APIs are usually documented so that developers know how to use and integrate with them.

Documentation can be in both human-readable and machine-readable forms. Human-readable documentation is designed for developers to understand how to use the API. It may include detailed explanations, examples, and usage scenarios. Machine-readable documentation is designed to be processed by software for automating tasks like API integration and validation. It's written in structured formats like JSON or XML.

API documentation is often publicly available, particularly if the API is intended for use by external developers. If this is the case, always start your recon by reviewing the documentation.

Even if API documentation isn't openly available, you may still be able to access it by browsing applications that use the API.

To do this, you can use Burp Scanner to crawl the API. You can also browse applications manually using Burp's browser. Look for endpoints that may refer to API documentation, for example:

/api
/swagger/index.html
/openapi.json

If you identify an endpoint for a resource, make sure to investigate the base path. For example, if you identify the resource endpoint /api/swagger/v1/users/123, then you should investigate the following paths:

/api/swagger/v1
/api/swagger
/api

You could also use a list of common paths to directly fuzz for documentation.