MCPJam Inspector is the local development client for building and testing ChatGPT apps, MCP apps (Claude), and MCP servers. It provides a full widget emulator for instant iteration without ngrok or ChatGPT subscription requirements. Features ChatGPT Apps SDK support with windows.openai API (widgetState, callTool, structuredContent, sendFollowUpMessage, displayMode, CSP), MCP Apps (SEP-1865) with all JSON-RPC message types, and comprehensive OAuth debugging with visual inspection of every network message.
Additional capabilities include LLM playground with free access to frontier models (GPT-5, Claude Sonnet, Gemini 2.5) or custom API keys, MCP server debugging for local/remote connections with manual tool and resource invocation, server info viewing for icons/version/capabilities/instructions/widget metadata, and JSON-RPC observability. Apps Builder emulator supports Desktop/Tablet/Mobile views, locale changes, CSP permissions, light/dark mode, hover/touch, and safe area insets. Available via NPX (@mcpjam/inspector@latest) or desktop apps for Mac and Windows. Apache 2.0 license with active Discord community.
Use Cases:
www.mcpjam.com
npm version (https://img.shields.io/npm/v/@mcpjam/inspector?style=for-the-badge&color=blue) License: Apache 2.0 (https://img.shields.io/badge/License-Apache%202.0-blue.svg?style=for-the-badge) Discord (https://img.shields.io/badge/Discord-Join%20Server-5865F2.svg?style=for-the-badge&logo=discord&logoColor=white)
MCPJam Inspector is the local development client for ChatGPT apps, MCP apps (Claude), and MCP servers. Build and test your apps with a full widget emulator, chat with any LLM, and inspect your serverβs tools, resources, prompts, and OAuth flows.
No more ngrok or ChatGPT subscription needed. MCPJam is the fastest way to iterate on any MCP project.
Start up the MCPJam inspector:
npx @mcpjam/inspector@latest
Node.js (https://img.shields.io/badge/Node.js-20+-green.svg?style=for-the-badge&logo=node.js) TypeScript (https://img.shields.io/badge/TypeScript-5+-blue.svg?style=for-the-badge&logo=typescript)
We recommend starting MCPJam inspector via npx:
npx @mcpjam/inspector@latest
We also have a Mac and Windows desktop app:
| Capability | Description |
|---|---|
| ChatGPT Apps SDK | Local development for ChatGPT Apps SDK support. Full support for the windows.openai API: widgetState, callTool, structuredContent, sendFollowUpMessage, displayMode, CSP, and more. No more ngrok or ChatGPT subscription needed. Read more (https://www.mcpjam.com/blog/app-builder) |
| MCP Apps (Claude) | Full local development for MCP Apps (SEP-1865). Support for all JSON-RPC message types, such as tools/call, ui/initialize, ui/message, ui/open-link, and more. Read more (https://www.mcpjam.com/blog/mcp-apps-preview) |
| OAuth Debugger | Debug your MCP server's OAuth implementation at every step. Visually inspect every network message. Supports all protocol versions (03-26, 06-18, and 11-25). Support for client pre-registration, DCR, and CIMD. Read more (https://www.mcpjam.com/blog/oauth-debugger) |
| LLM playground | Chat with your MCP server against any LLM in the playground. We provide frontier models such as GPT-5 and Claude Sonnet for free, or bring your own API key. Playground supports ChatGPT apps and MCP Apps. Read more (https://www.mcpjam.com/blog/frontier-models) |
| MCP server debugging | Connect to and test any MCP server local or remote. Manually invoke MCP tools, resources, resource templates, and elicitation flows. View all JSON-RPC logs. Support for all features from the official MCP inspector. |
| Server info | View server icons, version, capabilities, instructions, and ChatGPT widget metadata exposed by the server. Read more (https://www.mcpjam.com/blog/server-instructions) |
Develop ChatGPT apps (https://developers.openai.com/apps-sdk/) and MCP apps (Claude) (https://github.com/modelcontextprotocol/modelcontextprotocol/pull/1865) in MCPJam's Apps Builder. Apps Builder is a local emulator to quickly view and iterate on your widgets.
window.openai messages in the logs.View every step of the OAuth handshake in detail, with guided explanations. Test with every version of the OAuth spec (03-26, 06-18, and 11-25). Support for client pre-registration, Dynamic Client Registration (DCR), and Client ID Metadata Documents (CIMD).
Try your server against any LLM model. We provide frontier models like GPT-5, Claude Sonnet, Gemini 2.5 for free, or bring your own API key. View your server's token usage.
MCPJam contains all of the tooling to test your MCP server. Test your server's tools, resources, prompts, templates, with full JSON-RPC observability. MCPJam has all features from the original inspector and more.
We're grateful for you considering contributing to MCPJam. Please read our contributing guide.
Join our Discord community (https://discord.gg/JEnDtz8X6z) where the contributors hang out at.
Some of our partners and favorite frameworks:
This project is licensed under the Apache License 2.0 - see the LICENSE.
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