#+TITLE: elisp-dev-mcp: MCP Server for Agentic Elisp Development

[[https://github.com/laurynas-biveinis/elisp-dev-mcp/actions/workflows/elisp-test.yml][https://github.com/laurynas-biveinis/elisp-dev-mcp/actions/workflows/elisp-test.yml/badge.svg]]
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[[https://melpa.org/#/elisp-dev-mcp][https://melpa.org/packages/elisp-dev-mcp-badge.svg]]
[[https://stable.melpa.org/#/elisp-dev-mcp][file:https://stable.melpa.org/packages/elisp-dev-mcp-badge.svg]]

* Overview

=elisp-dev-mcp= is an Emacs package that provides an MCP (Machine Code Protocol) server
for agentic Elisp development. It enables AI agents to assist with Elisp coding tasks
by providing a structured API to interact with Emacs and manipulate Elisp code.

This package leverages [[https://github.com/laurynas-biveinis/mcp-server-lib.el][mcp-server-lib.el]] for the underlying MCP infrastructure.

* Installation

From [[https://melpa.org/#/elisp-dev-mcp][MELPA]] or [[https://stable.melpa.org/#/elisp-dev-mcp][MELPA Stable]]:

=M-x package-install RET elisp-dev-mcp RET=

* Usage

** Registering with an MCP Client

After =mcp-server-lib= has been properly installed (including =M-x mcp-server-lib-install=), register =elisp-dev-mcp= with your MCP client:

#+begin_example
claude mcp add -s user -t stdio elisp-dev -- ~/.emacs.d/emacs-mcp-stdio.sh --init-function=elisp-dev-mcp-enable --stop-function=elisp-dev-mcp-disable --server-id=elisp-dev-mcp
#+end_example

Before using the MCP server, you must start it in Emacs with =M-x mcp-server-lib-start=. Stop it with =M-x mcp-server-lib-stop= when done.

** Available MCP Handlers

*** Elisp Function Documentation
- Name: =elisp-describe-function=
- Description: Get full documentation for an Emacs Lisp function
- Parameters:
  - =function=: The name of the function to describe (string)
- Returns:
  - =description=: The function's documentation (string)
  - or =error=: Error message if something went wrong (string)

*** Elisp Function Definition
- Name: =elisp-get-function-definition=
- Description: Get the source code definition of an Emacs Lisp function
- Parameters:
  - =function=: The name of the function to retrieve (string)
- Returns:
  - For Elisp functions:
    - =source=: The function's source code including header comments if present (string)
    - =file-path=: Path to the file where the function is defined (string)
    - =start-line=: First line number of the definition including header comments (1-based integer)
    - =end-line=: Last line number of the definition (1-based integer)
  - For C-implemented functions:
    - =is-c-function=: Boolean indicator that this is a C function (always true)
    - =function-name=: The name of the function (string)
    - =message=: A message indicating the function is implemented in C source code (string)

*** Elisp Variable Description
- Name: =elisp-describe-variable=
- Description: Get information about an Emacs Lisp variable without exposing its value
- Parameters:
  - =variable=: The name of the variable to describe (string)
- Returns:
  - =name=: Variable name (string)
  - =bound=: Whether variable is currently bound (boolean, false for declared but unbound variables)
  - =value-type=: Type of the value (string, e.g. "cons", "string", "integer")
  - =documentation=: Variable documentation or null if none (string or null)
  - =source-file=: Path to the file where the variable is defined (string)
  - =is-custom=: Whether it's a customizable variable (boolean)
  - =custom-group=: The custom group this variable belongs to (string, only present for custom variables)
  - =custom-type=: The custom type specification (string, only present for custom variables)
  - =is-obsolete=: Whether the variable is marked obsolete (boolean)
  - =obsolete-since=: Version when the variable became obsolete (string, only present if obsolete)
  - =obsolete-replacement=: Suggested replacement for the obsolete variable (string, only present if obsolete)
  - =is-alias=: Whether the variable is an alias for another variable (boolean)
  - =alias-target=: The variable this is an alias for (string, only present if alias)
  - =is-special=: Whether the variable is a special (dynamically scoped) variable (boolean)
  - or =error=: Error message if something went wrong (string)

*** Elisp Info Documentation Lookup
- Name: =elisp-info-lookup-symbol=
- Description: Look up Elisp symbols in Info documentation and return the complete documentation node
- Parameters:
  - =symbol=: The Elisp symbol to look up (string)
- Returns:
  - =found=: Whether documentation was found (boolean)
  - =symbol=: The symbol that was looked up (string)
  - =node=: The Info node name containing the documentation (string, when found)
  - =manual=: The Info manual name, typically 'elisp' (string, when found)
  - =content=: The complete Info node content including all examples, cross-references, and related information (string, when found)
  - =info-ref=: Info reference like '(elisp)Node Name' for direct access (string, when found)
  - =message=: Error or not-found message (string, when not found)

*** Elisp Source File Reader
- Name: =elisp-read-source-file=
- Description: Read Elisp source files from Emacs system directories or ELPA packages. Accepts either library names or absolute file paths.
- Parameters:
  - =library-or-path=: Library name (e.g., ="subr"=, ="org"=) or absolute path to =.el= file (string)
- Returns:
  - The complete file contents as a string
  - or =error=: Error message if library not found, file not found, invalid format, or access denied (string)
- Input modes:
  1. *Library names* (recommended for built-in and installed packages):
     - Simple names without path separators: ="subr"=, ="files"=, ="org"=
     - Resolved via Emacs =locate-library= function (searches =load-path=)
     - Examples: ="subr"=, ="mcp-server-lib"=, ="org"=
  2. *Absolute paths* (for compatibility with other =elisp-dev= tools):
     - Full paths ending in =.el=
     - Returned by =elisp-get-function-definition=
     - Examples: ="/opt/homebrew/.../lisp/files.el"=, ="/Users/name/.emacs.d/elpa/package-1.0/package.el"=
- Security:
  - Only reads from Emacs system lisp directories and ELPA directories
  - Rejects paths with =..= traversal
  - Resolves symlinks to prevent escaping allowed directories
  - Library names must resolve to paths within allowed directories
- Features:
  - Transparently handles =.el.gz= compressed files
  - Works with both built-in Emacs libraries and installed packages
  - Returns complete file contents as string

** Configuration for Alternative Package Managers

By default, =elisp-read-source-file= can only access Emacs system
directories and standard =ELPA= packages. For users of alternative
package managers like straight.el, elpaca, or custom package setups,
you can configure additional allowed directories:

#+begin_src elisp
(setq elisp-dev-mcp-additional-allowed-dirs
      '("~/.emacs.d/straight/build/"
        "~/.emacs.d/straight/repos/"
        "~/my-elisp-packages/"))
#+end_src

*Security Note:* Only add directories you trust, as this allows the
 MCP server to read any =.el= files in these locations.

* Similar packages

- [[https://codeberg.org/jlouisbiz/rcd-mcp-emacs-documentation][rcd-mcp-emacs-documentation]]

* License

This project is licensed under the GNU General Public License v3.0 (GPLv3) - see the LICENSE file for details.