Swagger is an open-source framework used for designing, building, documenting, and consuming RESTful web services. It provides a set of tools and specifications to help developers create APIs that are easy to understand and use. The core of Swagger is the OpenAPI Specification (OAS), a standard format for describing API endpoints, request parameters, responses, and authentication methods. With Swagger, developers can generate interactive API documentation that allows users to test endpoints directly from the documentation interface. It also includes tools for generating server and client code in various programming languages, streamlining the API development process. Swagger's ability to standardize and simplify API development ensures consistency, improves collaboration, and enhances the overall developer experience, making it a popular choice for building robust and maintainable APIs.