MCPJam Inspector
UnclaimedTest and develop ChatGPT and MCP apps locally without ngrok or ChatGPT subscription.
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TL;DR - MCPJam Inspector
- Locally test and develop ChatGPT and MCP apps.
- Emulates ChatGPT behavior, exposing API calls and JSON-RPC traffic.
- Includes OAuth debugger and LLM playground for testing with various models.
Pricing: Free plan available
Best for: Growing teams
What is MCPJam Inspector?
MCPJam Inspector is a local development tool designed for building and testing ChatGPT Apps SDK and MCP (ext-apps) applications. It provides an emulator that simulates ChatGPT's behavior, exposing all `windows.openai` API calls and JSON-RPC traffic, similar to Chrome DevTools for web applications. This allows developers to rapidly iterate on their apps without needing an ngrok tunnel or a ChatGPT subscription.
The tool also includes an OAuth debugger to visualize and verify MCP authorization flows against the MCP specification. Additionally, its LLM playground offers 1:1 emulation with ChatGPT, enabling developers to test their apps against various models, including frontier models like GPT-5, and view them in different display modes. MCPJam aims to streamline the development process for AI applications by providing a comprehensive local testing environment.
Available on: Web, macOS, Windows
Pros & Cons
Pros
- Useful for MCP protocol inspection
- Developer tool
- Open source
- Good for debugging
Cons
- Very niche use case
- Requires MCP knowledge
- Small user base
Preview
Key Features
MCP debuggingProtocol inspectionMessage loggingConnection testingError diagnosisDeveloper tools
Pricing Plans
Pricing checked Jul 28, 2026
Community
Free
- Test server primitives like tools, resources, prompts
- LLM playground for testing in real environments
- Playground free models or bring your own key
- Evals / pen test limited to 1 test case
- OAuth testing with dynamic client registration
- Collaboration features like share tools
- Up to 3 users per team
- Launch Inspector: npx@mcpjam/inspector@latest
Enterprise
Contact us
- Everything in Community, plus:
- Unlimited evals / pen test runs
- Integrate tests into your CI/CD
- Security and evals agent
- Server quality analysis agent
- Unlimited playground use with any model
- Advanced collaboration features
- No seat limits
- Customer success 24/7 support
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MCPJam Inspector FAQ
How does MCPJam Inspector facilitate local development for ChatGPT applications?
MCPJam Inspector provides a local emulator that simulates ChatGPT's behavior, exposing all
windows.openai API calls and JSON-RPC traffic. This allows developers to rapidly iterate on their ChatGPT Apps SDK and MCP applications without requiring an ngrok tunnel or a ChatGPT subscription.Which teams would benefit most from using MCPJam Inspector?
Teams developing ChatGPT Apps SDK and MCP (ext-apps) applications would find MCPJam Inspector most beneficial. It is designed for developers who need to test and debug their AI applications in a local environment before deployment.
How is MCPJam Inspector priced?
MCPJam Inspector is available on a free tier, allowing users to get started without initial cost. Paid plans are offered for those requiring more usage or additional features.
Can MCPJam Inspector help with OAuth authorization flows?
Yes, MCPJam Inspector includes an OAuth debugger specifically designed to visualize and verify MCP authorization flows. This feature ensures compliance with the MCP specification during the development process.
What kind of LLM testing capabilities does MCPJam Inspector offer?
MCPJam Inspector features an LLM playground that offers 1:1 emulation with ChatGPT. Developers can test their applications against various models, including frontier models, and view them in different display modes.
How does MCPJam Inspector compare to Playwright MCP for debugging?
MCPJam Inspector is specifically designed as a developer tool useful for MCP protocol inspection and debugging, providing an emulator for local testing. Playwright MCP, while also a testing tool, focuses on browser automation rather than direct MCP emulation and debugging.
What are the main trade-offs when choosing MCPJam Inspector?
MCPJam Inspector addresses a very niche use case, requiring specific knowledge of the MCP protocol. Its specialized nature means it caters to a smaller user base compared to more general development tools.
Source: mcpjam.com