bun-uia — Claude Code MCP server: drive Windows GUI
An MCP server that hands your coding agent control over native Windows windows through UI Automation. Useful when the target app is a desktop program, not a browser.
claude mcp add --env BUN_UIA_PROFILE=<BUN_UIA_PROFILE> --env BUN_UIA_OS=<BUN_UIA_OS> --env BUN_UIA_ALLOW=<BUN_UIA_ALLOW> --env BUN_UIA_DENY=<BUN_UIA_DENY> --env BUN_UIA_CURSOR=<BUN_UIA_CURSOR> --transport stdio bun-uia -- npx -y bun-uiaWhat bun-uia does
bun-uia is a Bun-based MCP server that exposes Windows UI Automation to an AI agent. The agent can walk the element tree of a native window, read control state, and act on it. The author pitches it as Playwright for the Windows desktop.
It runs over stdio with npx -y bun-uia. Configuration comes through environment variables: BUN_UIA_PROFILE, BUN_UIA_OS, BUN_UIA_ALLOW, BUN_UIA_DENY, BUN_UIA_CURSOR. The allow and deny lists decide which applications the agent may touch. Skip them and the server still starts, but nothing scopes its reach across your machine.
Windows is the only supported target, since UI Automation lives there. On macOS or Linux there is no API to bind to, so the server has nothing to talk to. You need Node.js or Bun available for npx to work.
What it helps with
- read the element tree of a native Windows window
- click a button in a desktop app from the agent
- restrict which applications the agent can reach
- script a GUI workflow without manual clicking
- pull control state out of a window as text
Example prompts for the agent
- Connect to the Notepad window and list the elements inside it
- Find the Save button in the open window and click it
- Limit the agent to
calc.exeand report what it can see
How to install bun-uia
Platform CLI
claude mcp add --env BUN_UIA_PROFILE=<BUN_UIA_PROFILE> --env BUN_UIA_OS=<BUN_UIA_OS> --env BUN_UIA_ALLOW=<BUN_UIA_ALLOW> --env BUN_UIA_DENY=<BUN_UIA_DENY> --env BUN_UIA_CURSOR=<BUN_UIA_CURSOR> --transport stdio bun-uia -- npx -y bun-uiaReplace <…> with your own values. 1 more environment variable is in the server README
Platform CLI
codex mcp add bun-uia --env BUN_UIA_PROFILE=<BUN_UIA_PROFILE> --env BUN_UIA_OS=<BUN_UIA_OS> --env BUN_UIA_ALLOW=<BUN_UIA_ALLOW> --env BUN_UIA_DENY=<BUN_UIA_DENY> --env BUN_UIA_CURSOR=<BUN_UIA_CURSOR> -- npx -y bun-uiaReplace <…> with your own values. 1 more environment variable is in the server README
Config file
{
"mcpServers": {
"bun-uia": {
"command": "npx",
"args": [
"-y",
"bun-uia"
],
"env": {
"BUN_UIA_PROFILE": "<BUN_UIA_PROFILE>",
"BUN_UIA_OS": "<BUN_UIA_OS>",
"BUN_UIA_ALLOW": "<BUN_UIA_ALLOW>",
"BUN_UIA_DENY": "<BUN_UIA_DENY>",
"BUN_UIA_CURSOR": "<BUN_UIA_CURSOR>"
}
}
}
}Replace <…> with your own values. 1 more environment variable is in the server README
Config file
{
"servers": {
"bun-uia": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"bun-uia"
],
"env": {
"BUN_UIA_PROFILE": "<BUN_UIA_PROFILE>",
"BUN_UIA_OS": "<BUN_UIA_OS>",
"BUN_UIA_ALLOW": "<BUN_UIA_ALLOW>",
"BUN_UIA_DENY": "<BUN_UIA_DENY>",
"BUN_UIA_CURSOR": "<BUN_UIA_CURSOR>"
}
}
}
}Replace <…> with your own values. 1 more environment variable is in the server README
Platform CLI
gemini mcp add -e BUN_UIA_PROFILE=<BUN_UIA_PROFILE> -e BUN_UIA_OS=<BUN_UIA_OS> -e BUN_UIA_ALLOW=<BUN_UIA_ALLOW> -e BUN_UIA_DENY=<BUN_UIA_DENY> -e BUN_UIA_CURSOR=<BUN_UIA_CURSOR> bun-uia npx -y bun-uiaReplace <…> with your own values. 1 more environment variable is in the server README
Step by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about bun-uia
How do I install bun-uia in Claude Code?
Run claude mcp add bun-uia -- npx -y bun-uia. To pass environment variables, use the longer form: `claude mcp add --env BUN_UIA_PROFILE=<BUN_UIA_PROFILE> --env BUN_UIA_OS=<BUN_UIA_OS> --env BUN_UIA_ALLOW=<BUN_UIA_ALLOW> --env BUN_UIA_DENY=<BUN_UIA_DENY> --env BUN_UIA_CURSOR=<BUN_UIA_CURSOR> --transport stdio bun-uia -- npx -y bun-uia`.
What does bun-uia do?
It gives an agent access to Windows UI Automation: finding elements in native windows, reading their state, and acting on them. It speaks MCP over stdio.
Which systems does bun-uia run on?
Windows only, because UI Automation is part of that OS. There is no way to start the server on macOS or Linux.
