davidpham87/mcp-bb-clj

mcp-bb-clj

An MCP server/client written in clojure for babashka

Implementation of MCP protocol (https://modelcontextprotocol.io/specification/2025-06-18/schema) using only babashka (clojure) libraries https://book.babashka.org/#libraries

Split implementation:

• Data manipulation through pure functions
• Expose the function using http-skit server.
• Make a client as well.

Inspiration:

• https://github.com/hugoduncan/mcp-clj

Tools

The server comes with several built-in tools:

• cljfmt: Formats Clojure code using cljfmt.
  • Input: code (string)
• zprint: Formats Clojure code or EDN using zprint.
  • Input: code (string), options (optional EDN string)
• find-malformed-delimiters: Checks Clojure code for malformed delimiters.
  • Input: code (string)
• clj-kondo: Lints Clojure code using clj-kondo.
  • Input: code (string)
  • Prerequisite: The clj-kondo binary must be installed and available in the system PATH.
• echo: Echoes the input text.
• Malli Tools: Tools for working with Malli schemas (validate-schema, generate-sample, infer-schema).

Adding new Tools and Prompts

Adding a Tool

To add a new tool, define it as a map and register it in src/mcp_bb_clj/core.clj.

1. Define the tool:

   A tool definition requires a :name, :description, :inputSchema (JSON Schema), and an :implementation function.

   Example:

   (def my-tool
     {:name "my-tool"
      :description "A custom tool description"
      :inputSchema {:type "object"
                    :properties {"arg" {:type "string"}}
                    :required ["arg"]}
      :implementation (fn [{:keys [arg]}]
                        {:content [{:type "text" :text (str "You said: " arg)}]})})
   

2. Register the tool:

   Add the tool to the mcp-server/add-tool! call in src/mcp_bb_clj/core.clj.

   (mcp-server/add-tool! mcp-server
                         {:tools [echo-tool
                                  my-tool]})
   

Adding a Prompt

Prompts can be defined similarly and used as templates.

1. Define the prompt:

   (def my-prompt
     {:name "explain-code"
      :description "Explains the provided code."
      :arguments {:type "object"
                  :properties {"code" {:type "string"}}
                  :required ["code"]}
      :messages [{:role "user"
                  :content "Explain this code:\n\n{{code}}"}]})