vellum-ai 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.