MockPro - API & Stream Mocker

MockPro is a powerful Chrome extension for developers who need to intercept and mock network requests without setting up external tools or proxy servers. It works entirely in the browser, supporting REST APIs, Server-Sent Events (SSE), and WebSocket connections. Whether you're building a frontend that depends on an unfinished backend, testing edge cases with specific API responses, or debugging streaming connections, MockPro gives you full control over what your application sees — with zero configuration on the server side. KEY FEATURES REST API Mocking Intercept fetch() and XMLHttpRequest calls Set custom status codes, headers, and response bodies Match requests by URL pattern, HTTP method, headers, and body content Support for wildcard (*) and regex URL patterns SSE (Server-Sent Events) Mocking Intercept EventSource connections Define custom event sequences with configurable delays Support for named event types Optional repeat/loop mode for continuous streaming WebSocket Mocking Intercept WebSocket connections Define messages sent on connect Create response rules that match incoming messages Echo client messages with the {{message}} template Advanced Matching URL wildcards: https://api.example.com/users/* Regex patterns: //api/v[0-9]+/users/ Header matching: only mock when specific headers are present Body matching: only mock when request body contains specific text Developer Experience Professional code editor with JSON syntax highlighting (CodeMirror 6) Built-in search and replace (Ctrl+F) with match highlighting JSON Tree View to visualize response structure One-click JSON formatting Request logging with real-time monitoring Import/Export rules as JSON for team sharing Delay simulation to test loading states Per-rule enable/disable toggle Global on/off switch HOW IT WORKS Open the MockPro dashboard from the extension popup Create a new rule — choose REST, SSE, or WebSocket Set a URL pattern to match Define your mock response Enable the rule and refresh your page MockPro injects a lightweight interceptor into web pages that catches matching network requests before they reach the server, returning your configured responses instantly. USE CASES Frontend development when backend APIs are not ready Testing error states (500, 404, 403 responses) Simulating slow network responses with delay Mocking real-time data streams (SSE/WebSocket) Reproducing specific API behaviors for debugging Demo and presentation environments QA testing with controlled API responses NEW IN 2.4 — CLAUDE CODE / MCP INTEGRATION Pair MockPro with the optional mockpro-mcp server (npm) to let Claude Code or any MCP client drive the extension directly from your editor: • Create, update, toggle, delete rules without leaving the IDE • Generate rules from OpenAPI specs in one command • Record live traffic and replay as fixtures • Inspect any open tab — read console logs, network logs, WebSocket frames • Query DOM, simulate clicks/typing, navigate tabs • Subscribe to real-time per-tab streams via MCP resources Setup: install the extension, then run: claude mcp add --scope user --transport stdio mockpro -- npx -y mockpro-mcp --extension-id <YOUR_ID> The MCP server runs locally on 127.0.0.1:27319 — no data leaves your machine. All write tools can be disabled via --readonly flag. DEVELOPER TOOLS TAB The extension also bundles 20+ utility tools — JSON formatter, Base64 encoder, JWT decoder, regex tester, image converter, color picker, hash generators, and more — accessible directly from the dashboard. PRIVACY MockPro works entirely locally in your browser. No data is sent to external servers. All rules and configuration are stored in Chrome's local storage. See our privacy policy for details. OPEN SOURCE MockPro is free and open source. Contributions and feedback are welcome.