Writing an MCP Server Using Only Notepad

This verifies whether an MCP (Model Context Protocol) server can be built using only Windows' default Notepad, in a client environment where all external runtimes and IDEs are blocked.

As an alternative, it leverages the JavaScript-based execution engine built into the operating system. Referencing WelsonJS as an example that runs without external development tools, the server is implemented using only the built-in runtime.

The key point is that MCP operates over stdio and JSON-RPC 2.0.

• Request: MCP Client → stdin
• Response: MCP Server → stdout

To prevent console messages from contaminating the protocol, output is controlled with options like /quiet, and mcploader.js is written using the StdioServer and JsonRpc2 libraries.

The example tools are two: add_both_numbers and evaluate_js_es3. After registering the cscript command along with app.js, mcploader, and /quiet in Claude Desktop's claude_desktop_config.json and restarting, you check in the developer menu whether local-tools shows a running status.

Finally, by requesting number addition or JavaScript ES3 execution in the chat, it is verified that the MCP server actually responds.