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

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

Usage

See the README.md in the example/cljc-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

Contributing

Only code typed and reviewed by a human will be accepted for review, discussion, and maybe merged. We have a policy of keeping the source code clean, organized, and easy to read for a human.

Advices for improving the chances for your PR to be accepted:

• Keep your PR small and in line with an associated Github issue.
• If you plan some significant changes, it's best to discuss them in an issue first, to keep the contribution aligned with the technical direction of project.
• Do not reformat the source code unless you found a formatting issue, in which case you should use a separate PR just for that.

License

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

Copyright (c) Metosin and contributors.