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MCP

MCP lets an AI agent, such as Claude Code, work in the editor you're using. It gets the same access you have: your buffers, commands and ex commands. It's off until you turn it on.

Turning it on

Add this to init.scm:

(mcp-enable!)

The editor then listens on a socket only you can reach, $XDG_RUNTIME_DIR/imp/mcp.sock. An agent connects by running imp --mcp as its MCP server. For Claude Code:

claude mcp add imp -- imp --mcp

An agent with this access can evaluate Scheme, and so run anything you could. Turn it on only for agents you'd trust with your shell.

What an agent can do

An agent can:

  • List, read and edit buffers, including unsaved changes.
  • Open files and save buffers.
  • See where your cursor is, and move it.
  • Search a buffer.
  • Run a named command, or an ex command.
  • Read the language servers' errors and warnings.
  • Evaluate Scheme in the running editor.

Watching what it does

Each change an agent makes shows on the status line, starting with agent:. :mcp-log lists them all. Each edit an agent makes is one undo step, so u takes it back.

Adding a tool

define-mcp-tool! gives agents a tool of your own. It takes a name, a description, a JSON Schema for the arguments, and a procedure. The procedure gets the arguments and returns text.

(define-mcp-tool! "word_count"
  "Count the words in the current buffer."
  (schema '() '())
  (lambda (args)
    (number->string (length (split-whitespace (buffer-substring 0 (buffer-length)))))))

(schema '() '()) is a schema with no arguments.