Postman API is a web-based, free, and stable tool used in building, managing, creating requests, backend testing, publishing, sharing, and documenting APIs. It's an API client that helps developers build, visualize data, authenticate, and manage APIs developed in REST, GraphQL, and SOAP. Postman automates tests in Continuous Integration (CI) or Continuous Delivery (CD) pipelines, making software development easy and quick. The tool allows developers to design API schema, simulate responses, detect bugs, and mock servers. It also enables the production of an API that runs as expected before it's released for consumer use. Postman is accessible through the web with a Chrome extension or desktop application for Mac, Windows, and Linux. The tool provides multiple environments and integration options, saves time by scheduling and automating tests, and simplifies monitoring. It also offers a free framework, user-friendly interface, and tutorials to help developers get started.