Pure JSON-RPC 2.0 over stdio. Zero dependencies. Full Model Context Protocol compliance. Drop it into Claude Desktop and go.
Most MCP tutorials start with an SDK that pulls in dozens of transitive dependencies. You inherit their bugs, their breaking changes, and their opinions about how your server should work.
MCP Server Builder gives you a working JSON-RPC server with zero external packages. One file. Standard Node.js. You understand every line because there's nothing hidden behind a framework.
Handles initialize, notifications/initialized, tools/list, and tools/call. Proper handshake sequence, correct response format, no shortcuts.
JSON-RPC 2.0 error codes for parse errors (-32700), invalid requests (-32600), method not found (-32601), and invalid params (-32602). Structured failures, not crashes.
No npm install. No node_modules. Just Node.js 18+ and your code. Works offline, deploys anywhere, audits in minutes.
Ships with echo and add tools as working examples. See the pattern, copy it, add your own tools in minutes.
Add a tool definition to the array, add a handler case, return the result. No decorators, no config files, no build step. Three changes and you're done.
node pure-jsonrpc-server.js starts reading JSON-RPC from stdin and writing responses to stdout. That's the entire startup sequence.
Define a tool in the TOOLS array with a name, description, and input schema. Write a handler function that takes arguments and returns results. No framework to learn.
Point Claude Desktop, Claude Code, or any MCP client at your server. The protocol handshake happens automatically. Your tools show up in Claude's tool list.
One-time purchase. Source code is yours forever.
Tell us which API you need Claude to access. We'll scope it and get back to you within 24 hours.
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