You can invoke an API using the integrated API Console or a third-party tool like cURL.
WSO2 API Manager has an integrated API ConsoleSwagger UI, which is developed using the Swagger UI. Swagger UI is part of the Swagger project.
Swagger is is a 100% open source, standard,language language-agnostic specification agnostic specification and a complete framework for describing, producing, consuming, and visualizing RESTful APIs, without the need of a proxy a proxy or third-party services. Swagger allows consumers to understand the capabilities of a remote service without accessing its source code and interact with the service with a minimal amount of implementation logic. Swagger helps describe a services in the same way that interfaces describe lower-level programming code.
Also, see the Swagger 2.0 specification.