cl-mcp

MCP server and client framework for Common Lisp.

Server: expose any CL function as an MCP tool — make-server → register-tool → run-server.

Client: connect to any MCP server subprocess, list tools, call tools — make-client → connect → list-tools / call-tool.

Framework handles JSON-RPC 2.0 framing, NDJSON stdio transport, MCP protocol negotiation, tool validation, threading, and error recovery. Consumer code is pure business logic.

Protocol: MCP 2025-06-18 (server) / 2025-11-25 (client) | Language: Common Lisp (SBCL) | License: MIT

Ships dev and integration SKILLS for your agent.

Quick Start — Server

sbcl --load cl-mcp.asd --eval "(ql:quickload :cl-mcp)"

(defvar *server* (cl-mcp:make-server :name "my-server" :version "1.0.0"))
(cl-mcp:register-tool *server* "ping"
  :description "Returns pong"
  :schema '(("type" . "object"))
  :handler (lambda (args) (declare (ignore args)) "pong"))
(cl-mcp:run-server *server*)

Quick Start — Client

sbcl --load cl-mcp.asd --eval "(ql:quickload :cl-mcp/client)"

(cl-mcp.client:with-mcp-client (client
    :name "my-agent"
    :command '("npx" "@modelcontextprotocol/server-filesystem" "/tmp"))
  (let ((tools (cl-mcp.client:list-tools client)))
    (format t "Available tools: ~{~a~^, ~}~%"
            (mapcar (lambda (t) (getf t :name)) tools)))
  (let ((result (cl-mcp.client:call-tool client "read_file"
                                         '(("path" . "/tmp/hello.txt")))))
    (print (getf result :content))))

Documentation

Document	Audience	Purpose
.claude/skills/integration/SKILL.md	Consumers	Using cl-mcp (server + client) in a project
.claude/skills/dev/SKILL.md	Contributors	Working on cl-mcp

Running Tests

# Server tests
sbcl --load cl-mcp.asd \
     --eval "(ql:quickload :cl-mcp/tests)" \
     --eval "(asdf:test-system :cl-mcp)"

# Client tests
sbcl --load cl-mcp.asd \
     --eval "(ql:quickload :cl-mcp/client-tests)" \
     --eval "(asdf:test-system :cl-mcp/client)"

Authors

Abhijit Rao / quasi / quasiLabs