Swagger is an open-source tool that helps developers design, build, and document RESTful APIs (Application Programming Interfaces). Swagger provides a set of rules for how to describe APIs in a common language that everyone can understand.
Swagger is comprised of a mix of open-source, free and commercially available tools that aid in the API lifecycle. Swagger tools are broadly divided into two categories: Swagger definition tools (like Swagger Editor, Swagger UI, and Swagger Codegen), which are used for designing, building, and documenting APIs, and Swagger inspection tools (like Swagger Inspector), used for testing and validating APIs.
Swagger helps developers define APIs in a common format (OpenAPI Specification), and its tools allow these APIs to be built, used, and tested without the need for manual intervention.