MockPro - API & Stream Mocker

Tracking since Apr 11, 2026.

Changelog

• Jun 4, 2026
  description

  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
  
  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.

  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.

• May 29, 2026
  permissions

  storage, tabs

  storage, tabs, alarms

Permissions & access

Permissions

storagetabsalarms

Host access

None declared

Screenshots