Response Mocker Doctor Ultimate is a Chrome extension designed to facilitate HTTP and WebSocket request mocking with exceptional precision. This tool allows developers to simulate various API responses, including error codes and unusual WebSocket messages, by intercepting requests directly through Chrome's DevTools Protocol. Users can match requests based on URLs, methods, bodies, headers, and query parameters using substring, glob, or regex matching modes. The extension also supports CORS configurations with a single click, making it easier to work with cross-origin requests.

In addition to HTTP mocking, the extension provides robust WebSocket support, enabling users to intercept WebSocket messages and reply with custom server messages. The tool includes features like JavaScript predicates for dynamic rule matching, and the ability to craft dynamic responses that can vary based on incoming requests. With a user-friendly interface, features such as rule import/export, and a master toggle for easy management, Response Mocker Doctor Ultimate streamlines the process of testing front-end applications against diverse backend scenarios.