MCP Toolkit

This library is a very unofficial MCP SDK in Clojure.

It handles the communication between MCP clients and MCP servers, and attempts to provide a Clojure-ish experience to developers working on expending the MCP ecosystem.

Status: alpha quality

Tested on Claude Desktop and Claude Code, no problems found for the features implemented.

Implemented features

• [x] API for both clients & servers
• [x] CLJC
  • [x] Clojure
  • [x] Clojurescript
  • [ ] Babashka
• I/O agnostic library
• Uses Promesa to support async tasks in prompts, resources and tools
• Compatible with protocol versions
  • [x] 2024-11-05
  • [x] 2025-03-26
  • [ ] 2025-06-18 (not yet)
• MCP features implemented
  • [x] Cancellation
  • [x] Ping
  • [x] Progress
  • [x] Roots
  • [x] Sampling
  • [x] Prompts
  • [x] Resources
  • [x] Tools
  • [x] Completion
  • [x] Logging
  • [ ] Pagination
• Example projects
  • [x] MCP server in CLJC, uses STDIO transport
  • [x] MCP client in CLJC, connects to the server above using STDIO transport
  • [x] MCP server in CLJ, uses HTTP with SSE transport
  • [ ] [MCP server in CLJ], uses Streamable HTTP transport (PR welcome)

Usage

See the README.md in the example-server-stdio/ project to learn:

• how to use this library to make your own MCP server in Clojure, and
• how to develop its components (prompts, resources and tools) via the REPL while the server is running.

Additionally, see the documentation on CLJDocs or in the doc/ directory.

Testing

npm install
./bin/kaocha --watch

Its place in the AI ecosystem

MCP toolkit aims to be more convenient for the Clojure community than the official MCP SDKs for Java or Typescript.

It provides utilities to build an MCP server in Clojure(script), but doesn't provide any prompts, resources or tools to help working on a Clojure codebase. It is typically used for building general purpose MCP stuffs.

Other MCP libs

• MCP Clojure SDK: similar library, discovered after being mostly done implementing this one 😅
• Calva's Backseat Driver
• Clojure MCP
• Modex

License

This project is distributed under the Eclipse Public License v2.0.

Copyright (c) Metosin and contributors.