Postman is an API development tool that began as a way to send HTTP requests and inspect responses, and grew into a broad platform for working with APIs. On its own product page Postman describes itself as a unified platform for designing, testing, distributing, documenting, and monitoring APIs, and positions itself as one of the most widely used API platforms in the world.
The tool started in 2012 as a simple browser extension built to make sending and replaying API requests easier than hand-crafting them with command-line utilities. From that origin it expanded into a standalone desktop application and a collaborative web service used by large teams to share and govern their API work.
Two organizing concepts sit at the center of Postman. Collections group related requests together so that whole workflows can be saved, shared, run, and reused, while environments hold sets of variables, such as base URLs, tokens, and keys, that let the same collection run against different deployment contexts like local, staging, and production by swapping the active environment.
Beyond manual request building, Postman’s own documentation describes capabilities for testing and automation, including a collection runner that executes requests in sequence and scripting that adds dynamic behavior and assertions to requests. These features let teams turn ad hoc API calls into repeatable test suites that can run inside continuous integration pipelines.
Postman also generates documentation from collections and API specifications and supports designing APIs from definitions, connecting the request-building experience to formal description formats. In doing so it sits alongside specification tools such as Swagger and the OpenAPI Specification, giving developers a single environment in which to design an API, exercise it, write tests against it, and publish documentation for its consumers.