Swagger is a very good open-source tool for documenting   APIs provided by microservices. It provides very easy to use interactive documentation. By the use of swagger annotation on REST endpoint, api documentation can be auto-generated and exposed over the web interface. An internal and external team can use web interface, to see the list of APIs and their inputs & error codes. They can even invoke the endpoints directly from web interface to get the results. Swagger UI is a very powerful tool for your microservices consumers to help them understand the set of endpoints provided by a given microservice.