MCPJam Inspector
MCPJam Inspector is a comprehensive local testing and debugging tool for ChatGPT apps and MCP servers that provides a widget emulator, LLM playground, and OAuth debugging capabilities.
https://www.mcpjam.com/?ref=producthunt
Product Information
Updated:Feb 9, 2026
What is MCPJam Inspector
MCPJam Inspector is an open-source, enterprise-grade development tool designed specifically for interacting with Model Context Protocol (MCP) servers. It serves as a local-first development platform that allows developers to test and debug their ChatGPT apps, MCP apps (ext-apps), and MCP servers. Built as a modern monorepo with React + TypeScript frontend, Express.js backend, and CLI components, it provides a complete testing environment without requiring external dependencies like ngrok or ChatGPT subscriptions.
Key Features of MCPJam Inspector
MCPJam Inspector is a comprehensive local development and testing tool for ChatGPT apps and MCP servers, offering a React-based interface with real-time server connection management, tool execution, resource browsing, and chat capabilities across multiple AI providers. It supports multiple protocols (STDIO, SSE, Streamable HTTP), provides JSON-RPC observability, and includes features like an LLM playground, OAuth debugging, and ChatGPT widget emulation.
Multi-Protocol Support: Supports STDIO, SSE, and Streamable HTTP protocols, allowing developers to test and debug MCP servers using different communication methods
LLM Playground Integration: Provides a testing environment with access to various language models, including frontier models like GPT-5, enabling developers to test their applications against different AI models
OAuth Flow Debugging: Offers visualization and debugging tools for MCP authorization flows, helping developers verify their OAuth implementation compliance with MCP specifications
ChatGPT Widget Emulation: Functions like Chrome DevTools for ChatGPT Apps, exposing all windows.openai API calls and JSON-RPC traffic while fully simulating ChatGPT's behavior
Use Cases of MCPJam Inspector
Local App Development: Developers can build and test ChatGPT apps locally without requiring ngrok or ChatGPT subscription, streamlining the development process
API Testing and Debugging: Similar to Postman, allows developers to test API endpoints, trigger tools, and debug error messages in MCP servers
Enterprise MCP Server Testing: Organizations can test their MCP servers' tools, resources, prompts, and templates with full JSON-RPC observability in a controlled environment
Pros
Open-source with active community development
Comprehensive feature set compared to the original inspector
Local-first development approach eliminating external dependencies
Cons
Some features are still in beta and need polishing
Relatively new fork of the original inspector, may have stability issues
How to Use MCPJam Inspector
Install MCPJam Inspector: Run 'npx @mcpjam/inspector@latest' in your terminal to install and start the inspector. By default, it will start on port 3000.
Configure Custom Port (Optional): To use a different port, run 'npx @mcpjam/inspector@latest --port 4000' replacing 4000 with your desired port number
Connect Your MCP Server: Once the inspector starts, add your MCP server through the UI. You can configure server settings including name, type (stdio/http), URL, headers, and OAuth settings if needed
Test Tools and Resources: Use the inspector interface to view and manually trigger your server's tools, resources, prompts and templates. You can test all features with full JSON-RPC observability
Use LLM Playground: Test your server against different LLM models in the playground environment. You can use local models through Ollama or test against provided frontier models
Debug OAuth Flows: If your server uses OAuth, use the OAuth debugger to visualize and verify your authorization flows conform to MCP specifications
Test ChatGPT Apps: Use the ChatGPT Apps Builder feature to test apps locally with the widget emulator that simulates ChatGPT's behavior and exposes windows.openai API calls
Monitor JSON-RPC Logs: View all JSON-RPC traffic and message types like tools/call, ui/initialize, ui/message, and ui/open-link for debugging purposes
MCPJam Inspector FAQs
MCPJam Inspector is a local development client for testing and debugging ChatGPT apps, MCP ext-apps, and MCP servers. It works similar to Postman for API endpoints, allowing developers to trigger tools, test authentication, and debug their applications.
MCPJam Inspector Video
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