# Computer Use

> Control a connected desktop

- Skill: `vellum-ai/computer-use` (Agent Skill, multi-file: 13 files)
- Install (CLI): `npx skillmds@latest add vellum-ai/computer-use`
- Raw SKILL.md: https://api.skillmd.com/api/skills/vellum-ai/computer-use/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: vellum-ai (https://skillmd.com/u/vellum-ai)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/vellum-ai/computer-use

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This skill provides the computer_use_* action tools for controlling a
connected desktop. CU tools run through the main agent loop via HostCuProxy.

The skill is internally preactivated for conversations with a connected desktop client.

Tools in this skill are proxy tools. Execution is forwarded to a connected
desktop client and is never handled locally by the assistant.

## Window-scoped observation (macOS)

`computer_use_observe` accepts optional `capture_window_id`, a native macOS
CGWindowID (not a browser tab ID or accessibility element ID). Obtain the ID
from a current native window inventory before using it; never guess one.
The native helper captures that window and its accessibility tree without
including secondary windows, even when another app covers the selected window.
A missing window must not be replaced with a desktop capture.

This is a **single observation**, not a session-wide privacy boundary: normal
click/type/scroll and other action tools still return their normal desktop
observations. Do not promise app-only capture for a whole control session.
The desktop must explicitly advertise `host_cu_window_capture` support on its
connection; the daemon rejects older or unsupported clients before requesting
any capture. Other desktop platforms reject this option.

The screenshot is window-relative, while action coordinates are screen points;
do not scale it using full-display dimensions. Prefer accessibility element IDs
and ensure the intended window is focused before a later action. Window-scoped
observation does not focus the window or confine subsequent input to that app.