MockServer

MockServer is an open-source tool for mocking and proxying HTTP and HTTPS services, enabling teams to simulate external systems for testing, development, and CI pipelines. It can run as a standalone server, be embedded in tests, or operate inside containers, such as Docker, to fit into existing workflows.

The core functionality centers on defining expectations that map incoming requests to predefined responses. Users can specify matchers based on method, path, headers, or body, and return custom status codes, headers, and bodies. MockServer also supports request verification to confirm that expected requests occurred, as well as scenario-based workflows to model multi-step interactions. In proxy mode, it can forward unmatched traffic to real endpoints and can record interactions for later replay. Features such as response templating, delay injection, and fault simulation help simulate realistic service behavior and latency.

Typical use cases include isolating test environments from fragile or unavailable external services, validating client-side error handling, and driving end-to-end tests with stable responses. It is commonly employed in integration and contract testing, performance testing, and automated test suites. The tool provides a REST API and client libraries (notably Java and JavaScript) to programmatically define and manage mocks. It also offers a command-line interface and a Docker image, making it easy to integrate into build pipelines.

MockServer is released under an open-source license and has an active community contributing features and integrations. It is often compared with other API mocking tools and complements testing ecosystems by providing reliable, configurable service virtualization.