Clojure MCP SDK

A pure Clojure SDK for building Model Context Protocol (MCP) servers. This library provides everything you need to create MCP servers that work over both STDIO and HTTP transports.

Features

• Full MCP Protocol Support: Implements the complete MCP specification (protocol version 2025-06-18)
• Support all MCP types: tools, prompts, resources, and resource templates
• Dual Transport Support: Run servers over STDIO (standalone process) or HTTP (persistent server, easy to hack on)
• Capability negotiation: Request roots from the client if they support it, notify client of new tools/resources/prompts

Quick Start

Add to your deps.edn:

{:deps {co.gaiwan/mcp-sdk {:mvn/version "0.0.0}}}

Create a simple MCP server:

(ns simple-mcp-server
  (:require
   [co.gaiwan.mcp :as mcp]
   [co.gaiwan.mcp.state :as state]
   [malli.json-schema :as mjs]))

;; Add a tool
(state/add-tool
 {:name "greet"
  :title "Greeting Tool"
  :description "Sends a personalized greeting"
  :schema (mjs/transform [:map [:name string?]])
  :tool-fn (fn [req {:keys [name]}]
             {:content [{:type "text" :text (str "Hello, " name "!")}]
              :isError false})})

;; Add a prompt
(state/add-prompt
 {:name "joke-rating"
  :title "Joke Rater"
  :description "Rate how funny a joke is"
  :arguments [{:name "joke" :description "The joke to rate" :required true}]
  :messages-fn (fn [req {:keys [joke]}]
                 [{:role "user"
                   :content {:type "text"
                             :text (str "Rate this joke from 1-5:\n\n" joke)}}])})

#_(mcp/run-stdio! {})
(mcp/run-http! {:port 3999})

Development

This library uses Launchpad, use bin/launchpad to start a development process/REPL. See the Launchpad README for how to customize your deps.local.edn.

License

Copyright © 2025 Arne Brasseur

Licensed under the Apache License, Version 2.0.