MCPJam

MCPJam is an open-source, Postman-style testing and evaluation platform for MCP servers, letting developers test tools, prompts, resources, and authorization, compare models side by side, and read full request traces.

MCPJam is a local-first developer tool for testing, debugging, and inspecting MCP servers, as well as ChatGPT/OpenAI apps. As MCP adoption grows, developers need a reliable way to verify that their servers expose tools, prompts, and resources correctly and handle authorization properly, and MCPJam's Inspector is purpose-built for exactly that. The Inspector lets you connect a server, run its tools, and interactively test across many client configurations and models. It can compare multiple models side by side on the same prompt and surface the full user-to-agent-to-server trace for every call, making it much easier to debug why an MCP integration behaves the way it does. It also supports evaluations, so teams can measure MCP server behavior systematically. MCPJam Inspector runs three ways: a hosted web app requiring no install, a desktop app for Mac and Windows, or via the terminal. It is open-source and free, available on GitHub, making it an accessible standard tool for anyone building on MCP.