Mock Express is a browser extension designed for developers and testers, enabling the interception, inspection, and modification of HTTP requests and responses directly from Chrome. This tool is particularly beneficial for those working with unstable APIs, as it allows users to simulate various scenarios such as error states and latency. Key features include the ability to modify request headers and bodies, block specific requests, and delay requests to mimic slow network conditions.

Additionally, Mock Express provides functionality for response actions, allowing users to override real API responses with custom data, which is essential for testing frontend components without relying on backend services. The extension is lightweight, privacy-focused, and integrates seamlessly with modern frontend stacks, making it an ideal choice for frontend developers, QA engineers, and development teams looking to create stable testing environments.