Swagger - Powerful Opensource Framework for RESTful API

Swagger is the most powerful opensource framework for RESTful API.  As its opensource lots of developers are supporting it in many modern programming languages and environments.

It is based on OpenAPI specifications which defines a standard, language-agnostic interface to REST APIs which allows both humans and computers to discover and understand the capabilities of the service without access to source code, documentation, or through network traffic inspection. Actually since 1st January 2016 Swagger Specification has been donated to the Open API Initiative (OAI) and is the foundation of the OpenAPI Specification.

It contains a set of core tools that enable the usage of Swagger in a variety of situations, you can check out these tools here.

One of the best tool is Swagger Editor, it lets you edit API specifications in YAML inside your browser and to preview documentations in real time, and you have options of generating server or client code in different languages.

There are more other tools available but personally I feel using Swagger more easy, you can try it on below link and share your opinion in comment section

Swagger Editor

Swagger Homepage