Computer MCP

Computer MCP

Computer use you can actually leave running.

A macOS computer-use MCP server built for the part everyone skips: what happens in the hours you are not watching.

• It runs in every MCP client, not one app. Claude Code, Cursor, VS Code, Codex, or your own agent - one npx line, the same server everywhere. It is not tied to a single vendor's desktop app or plan.
• It does not take over your Mac. It presses buttons and fills fields in windows that stay behind the one you are in, and it leaves your pointer where you put it. When an app pulls itself to the front as it opens, the front is handed straight back and the reply says so - nothing is left stealing what you are typing.
• It does not pretend. When something is refused or fails, it says so and says why. The most common complaint about agents driving a computer is that they carry on as if it worked.
• Several can run at once. No session lock, no one-at-a-time limit. Writes to the shared log take a short file lock, so two servers cannot break the chain between them.
• It will not go near your passwords. Keychain, 1Password and five others are refused in the default mode (in the foreground - while an agent has the screen, or with CMCP_BACKGROUND=0 - they ask every time), and password fields are blacked out while the screenshot is still in memory. A screen recording leaves password managers out, but does not black out password fields.
• You can read back what it did. Every call lands in an append-only log, fingerprinted rather than stored in clear.
• Electron apps are not a blind spot. Slack, VS Code, Discord and Notion build their accessibility tree lazily, so most tools find an empty window. This one switches the tree on itself before it looks. Measured on a VS Code fork with two windows open: 0 buttons before, 728 after, same windows, same moment. CMCP_INGEN_ELECTRON=1 turns it off if you would rather the app did not pay for keeping a tree it otherwise would not build.

Honest limits: macOS only. It reads the accessibility tree, so an app that draws its own controls on a canvas and publishes nothing - some games, some plotting tools - is still a blind spot. A browser is a separate case: the switch above is an Electron API, and Chrome does not implement it. Measured on Chrome: 29 buttons before and after, unchanged. You get the browser's own window - tabs, toolbar, address bar - and the page inside it only when Chrome has built that tree itself (measured both ways, see the limits below). For a page, drive the browser with a browser tool.

No account, no API key, no model inside it. MIT.

npx @agent360/computer-mcp

No Swift needed: the package ships a universal binary for Apple silicon and Intel. It carries the ad-hoc signature macOS needs to run it at all - not a Developer ID signature, and not notarized. Gatekeeper may therefore ask you the first time.

computermcp.dev · Security model

Why

Handing an agent your keyboard, mouse and screen is the most useful thing you can give it and the least reversible. A screenshot of a working developer's Mac can contain a password manager mid-unlock, a .env open in the editor, or customer data. A stray keystroke in a terminal is not a typo - it is a command.

Most desktop-automation MCP servers hand all of that over at once, with no way to say *that, but not that*. So the careful people don't run them on the machine where the work actually is.

This is the same capability with the dangerous edges answered.

The three gates

1. Passwords never reach the model. Secure text fields and password-manager windows are painted opaque black on the bitmap *in memory*, before the PNG is written. There is no moment where an unredacted picture of your desktop exists as a file. Native fields expose the role AXSecureTextField; fields in a web page expose role AXTextField with the *subrole* AXSecureTextField. Checking only the role would catch native fields and let every browser password box through - so both are checked. In a web page the field is only found when the browser shows its page to the accessibility layer, and Chrome has done so on one and the same Mac at one time and not at another (see the limits below). Where it does not, the field is not painted over; what it shows is the browser's own dots, unless the page itself shows the password in plain text.

2. The dangerous places ask first. By default the agent works without interrupting you - that is what lets it run while you do something else - and every write is logged. What never goes through on its own: password managers and Keychain are refused in the default mode, because the menu bar cannot show what would be typed (in the foreground - while an agent has the screen, or with CMCP_BACKGROUND=0 - they ask *every single time*, even with allow), and that one is not configurable. Terminals and editors, where a keystroke can be a command, ask once per app per session. Quitting an app, closing a window, switching Space, and destructive-looking menu items ask every time; an action whose target app cannot be identified is refused in the default mode. The gate judges the app an action lands in: an app opened some other way - Spotlight, a shortcut - is guarded by what the agent then tries to do in it. Want a question before the first write too? Set CMCP_MODE=ask. If nobody answers, the answer is no.

3. Everything is written down. ~/.local/state/computer-mcp/audit.jsonl, mode 0600, append-only: every call, its target app, and whether it was allowed or refused with the reason. Every line carries its call's id, which together with the server's session id pairs the decision and the outcome of one call, even with several agents running. Each line also carries a fingerprint of itself and the line before it, so a removed or edited line breaks the chain. That is not a signature: whoever can write the file as you - including an agent with a terminal - can rewrite all of it. If you need proof against that, copy the log off the machine. If the log cannot be written - a full disk, a locked file - write actions are refused until it can. Two gaps remain: an action already under way when the disk fills can lack its outcome line, and typing that is cut off by the helper's time limit is logged as an error without saying how many characters arrived. Typed text is stored as a length and a *salted* SHA-256 prefix, never in clear - an audit trail full of passwords is its own breach. The salt is random per run and never written down, because an unsalted hash of a short password can be guessed offline by whoever holds the log. The honest cost: two actions can be compared within one run, not across runs.

Here is what that looks like, unedited. In the lines below an agent typed a sentence into TextEdit behind the window the person was using, asked in the menu bar to move a file to the Trash and got no answer (the run sets CMCP_ASK_TIMEOUT=1, so the question ended after a second and is logged as denied; with the default the call is logged as waiting and the question stays about ten minutes), then was refused when it tried to type into 1Password. They come from an isolated test run - its own state folder and stand-ins for the helper and the menu bar icon, so no real screen was touched and nobody's own log was read - which node scripts/log-uddrag.mjs repeats. In the presence fields, the idle times come from the stand-in helper and the icon version from the stand-in icon; the session count comes from the isolated state, and the surface is derived. Only the box setting was read from the Mac that made the run. A test checks that every line is byte for byte in the full log of that run and that its chain holds.

{"ts":"2026-10-20T18:52:45.701Z","session":"fabb2663","call":"746fffee","tool":"computer_type","tier":"write","args":{"app":{"length":8,"sha256_12":"1b330dc3a979","salted":true},"text":{"length":37,"sha256_12":"51f664abcb74","salted":true}},"target":"com.apple.TextEdit","mode":"allow","asker":"custom","decision":"allowed","asked":false,"reason":"CMCP_MODE=allow","l":1,"kaede":"e02a3d1b3560ea17"}

{"ts":"2026-10-20T18:52:45.705Z","session":"fabb2663","call":"746fffee","tool":"computer_type","tier":"write","target":"com.apple.TextEdit","phase":"executing","l":1,"kaede":"c1e763106513c3e7"} {"ts":"2026-10-20T18:52:46.112Z","session":"fabb2663","call":"746fffee","tool":"computer_type","outcome":"ok","effect":"sent","l":1,"kaede":"b053781eb3511c4d"} {"ts":"2026-10-20T18:52:47.761Z","session":"fabb2663","call":"88f2d9ae","tool":"computer_menu","tier":"write","args":{"app":{"length":6,"sha256_12":"0771e2f86fa0","salted":true},"path":"File > Move to Trash"},"target":"com.apple.finder","mode":"allow","asker":"menubar","presence":{"idle_at_ask":600,"idle_at_end":600,"server":"0.4.0","icon":"0.4.0","box":"on","sessions":1,"surface_derived":"box+menu"},"decision":"denied","asked":true,"reason":"background mode: nobody answered in the menu bar in time","l":1,"kaede":"9b82d6ae5a36942d"} {"ts":"2026-10-20T18:52:48.229Z","session":"fabb2663","call":"0ba79155","tool":"computer_type","tier":"write","args":{"app":{"length":9,"sha256_12":"84b5a01fae6a","salted":true},"text":{"length":7,"sha256_12":"b56e1d9fbfd2","salted":true}},"target":"com.1password.1password","mode":"allow","asker":"custom","decision":"denied","asked":false,"reason":"background mode: this would need a dialog, and a dialog takes the screen (a password app can never be approved from the menu bar)","l":1,"kaede":"1be981d7eeaf7445"}

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Each gate has a test, and each test has been mutation-checked: break the code on purpose and the test goes red. See Testing.

Install

# Claude Code

claude mcp add computer -- npx -y @agent360/computer-mcp

Or, inside Claude Code, as a plugin pinned to the version on npm:

/plugin marketplace add Agent360dk/computerMCP

/plugin install computer-mcp@agent360

// Cursor, VS Code, Codex CLI - mcp.json

{ "mcpServers": { "computer": { "command": "npx", "args": ["-y", "@agent360/computer-mcp"] } } }

Then grant two macOS permissions: System Settings → Privacy & Security → Accessibility, and the same under Screen Recording. Ask your agent to call computer_permissions and it will tell you what is still missing.

Which app do you grant them to? macOS attributes these to the *responsible process*, and which process that is depends on how you launched the server. Run from a terminal, it is usually the terminal. Run by an MCP client over npx, it may be the client instead. The honest answer is: grant it to whichever app the system dialog names, and if no dialog appears, start with the app that launched the client and check computer_permissions again.

Untested, and we would rather say so: we have not yet measured this from a

clean machine with permissions reset, so we cannot tell you with certainty

which of the two it will be in your setup. Upgrading is measured for

Accessibility (issue #4):

the grant belonged to the host app, not to our ad-hoc signed helper - a copy of

the helper with a different signature, started from a new path, still had it -

so in that setup an upgrade did not send anyone back to System Settings. Screen

Recording after an upgrade has not been measured