Urbit MCP

A general-purpose Model Context Protocol interface for Urbit.

Developer Setup

1. Build and Install

• Requires a running Urbit ship, real or fake, running on a machine you have terminal access to.

• Requires peru package manager. Install and set that up if you don't have it already. Make sure peru --version works.

Create and mount the desk on your Urbit ship:

> |new-desk %mcp
> |mount %mcp

In the urbit-mcp folder, run the build script. By default this will install dependencies into /dist in this folder. Use the -p argument to additionally copy the %mcp source and its dependencies into your ship's desk. This script will take a minute if it's your first time running it.

$ cd urbit-mcp
$ build.sh -p ~/path/to/zod/mcp

> |commit %mcp
> |install our %mcp

2. Authentication Setup

Get your ship's web login code from the Dojo:

> +code
lidlut-tabwed-pillex-ridrup
~zod:dojo>

Authenticate and get session cookie:

curl -i http://localhost:80/~/login -X POST -d "password=lidlut-tabwed-pillex-ridrup"

Extract the cookie from the set-cookie header, which will look like this:

urbauth-~your-ship=0v3.j2062.1prp1.qne4e.goq3h.ksudm

3A. Register with Claude

Add the MCP server to Claude using HTTP transport:

claude mcp add --transport http zod http://localhost:80/mcp --header "Cookie: urbauth-~your-ship=0v3.j2062.1prp1.qne4e.goq3h.ksudm" --scope user

3B. Register with Codex

Codex requires the mcp-proxy python package to function. Install with uvx mcp-proxy, then append this to your ~/.codex/config.toml:

[mcp_servers.fen]
command = "uvx"
args = [
  "mcp-proxy",
  "--transport", "streamablehttp",
  "--headers", "Cookie", "urbauth-~your-ship=0v2.20fhu.t7ki1.cftjr.3s8bv.d9i5l",
  "http://localhost:80/mcp"
]

Usage

Tools

Just ask! You can see the default tools here.

You can ask your LLM to add new Tools. Give it a description (and ideally, examples) and it will do its best, or provide a Hoon thread for it to adapt to run in %mcp-server. Threads in %mcp-server must be of signature $-((map @t argument:tool:mcp) shed:khan).

Prompts (slash commands)

MCP prompts for most default tools are available as slash commands, using the format /mcp__<mcp server>__<tool name>.

/mcp__zod__commit-desk mcp

Running these will append a predefined prompt to the conversation and call out to the LLM provider.

Type / in Claude Code to see available Prompts.

You can ask your LLM to add new Prompts. These can be any reusable snippet of text you like.

Resources (@ mentions)

MCP resources can be referenced with an @ mention to pull the contents into the context window.

@zod:https://docs.urbit.org/llms.txt

Type @ in Claude Code to see available Resources.

You can ask your LLM to add new Resources by providing an https:// URI to a public webpage or a beam:// URI to a file in Clay.

Development

Build Commands

• ./build.sh - Build full desk

• ./build.sh build-dev - Build dependencies

• ./build.sh clean - Clean build directories

• ./build.sh -p /path/to/desk - Build and copy to a ship's desk