mcp__unison__ucm_findLABSCO SUMMARY
The generic command tool is the reason this ages well.
Alongside the named tools there is one that passes any UCM command straight through, so a command the wrapper does not know about still works — at the cost of you needing to know the syntax, since errors are returned as UCM produced them. Point UCM at the same codebase from a terminal and you can watch what the assistant is doing rather than inferring it from tool output.
What it is
A Haskell MCP server that speaks to UCM, Unison's codebase manager, so an assistant can work in a Unison codebase directly. Because Unison stores code by content hash rather than in files, the usual read-and-edit approach does not apply — every operation here goes through UCM.
What you get
- Working with definitions —
mcp__unison__ucm_findto search,mcp__unison__ucm_viewfor source,mcp__unison__ucm_addfor new ones,mcp__unison__ucm_updatefor existing,mcp__unison__ucm_delete,mcp__unison__ucm_lsto list a namespace mcp__unison__ucm_runto evaluate an expression, andmcp__unison__ucm_testwhich generatesscratch.uwhen it is missingmcp__unison__ucm_dependenciesto show what a definition depends on- Projects and branches —
mcp__unison__ucm_list_projects,mcp__unison__ucm_switch_project,mcp__unison__ucm_project_create,mcp__unison__ucm_list_branches,mcp__unison__ucm_switch_branch,mcp__unison__ucm_branch_create,mcp__unison__ucm_merge - Libraries —
mcp__unison__ucm_lib_install,mcp__unison__ucm_share_installfor a specific version from Unison Share, andmcp__unison__ucm_share_search, which reports library information rather than performing a real search mcp__unison__ucm_commandas an escape hatch that runs any UCM command with its arguments, so commands added to UCM later still work — errors come back from UCM unchanged
Requirements
Unison installed and ucm on your PATH — brew install unisonweb/unison/unison-language on macOS. Building needs Haskell Stack; clone the repository and stack build, then find the binary with stack path --local-install-root. Register it with claude mcp add unison <YOUR_PATH_TO_BINARY_UNISON_MCP_SERVER> <YOUR_PATH_TO_UNISON_PROJECT> — the project directory is an argument, not an environment variable. To work in the same codebase from a terminal at the same time, start UCM with ucm --codebase <YOUR_PATH_TO_UNISON_MCP_SERVER>/.unison. MIT.
Setup effort
Build from source — git clone https://github.com/mizchi/unison-mcp.git
USE CASES
01
Finding out how something is defined
Search for the name, view the source, and read what it depends on without leaving the conversation.
02
Writing and checking a new function
Add the definition, evaluate an expression against it, and run the tests.
03
Working on a change in isolation
Create a branch, make the updates there, and merge when it holds together.
04
Pulling in a library
Install it, then list the lib namespace to see what names it brought with it.
05
Running a UCM command with no wrapper
Pass the command and arguments straight through when the named tools do not cover it.
20 tools
Listed in project docs. Your client may show a different list.
mcp__unison__ucm_addmcp__unison__ucm_runmcp__unison__ucm_viewmcp__unison__ucm_updatemcp__unison__ucm_lsmcp__unison__ucm_deletemcp__unison__ucm_testmcp__unison__ucm_dependenciesmcp__unison__ucm_list_projectsmcp__unison__ucm_switch_projectmcp__unison__ucm_project_createmcp__unison__ucm_list_branchesmcp__unison__ucm_switch_branchmcp__unison__ucm_branch_createmcp__unison__ucm_mergemcp__unison__ucm_lib_installmcp__unison__ucm_share_searchmcp__unison__ucm_share_installmcp__unison__ucm_commandBEFORE YOU INSTALL
What to know first
Tools you get
20 tools named in the project's documentation. The mcp__unison__ prefix in the documentation comes from registering the server as unison; the tool names themselves look like ucm_find. Every tool needs a working ucm on PATH.
INSTALLATION
Connect your client
You clone and build this one yourself.
Server setup
TERMINAL
git clone https://github.com/mizchi/unison-mcp.git
cd unison-mcp
stack build
stack path --local-install-root
claude mcp add unison <YOUR_PATH_TO_BINARY_UNISON_MCP_SERVER> <YOUR_PATH_TO_UNISON_PROJECT>MCP Clients
Claude Desktop
CLAUDE DESKTOP · JSON
{
"mcpServers": {
"unison": {
"command": "<YOUR_PATH_TO_UNISON_MCP_SERVER>/.stack-work/install/.../bin/unison-mcp-server-exe",
"args": [
"<YOUR_PATH_TO_UNISON_PROJECT>"
]
}
}
}Claude Code
CLAUDE CODE · TERMINAL
claude mcp add unison <YOUR_PATH_TO_BINARY_UNISON_MCP_SERVER> <YOUR_PATH_TO_UNISON_PROJECT>
