vellum-ai/app-control

This skill exposes the app_control_* proxy tools for driving a single named macOS application via raw input — keyboard, mouse, screenshot — that bypasses the system Accessibility tree. Use it only when explicitly directed to a specific app where the AX tree is unhelpful (emulators, games, OpenGL canvases, custom-rendered Electron apps). For general macOS UI navigation prefer the computer-use skill.

Tools in this skill are proxy tools — execution is forwarded to the connected macOS client, never handled locally by the assistant.

Cadence

Take 2-3 actions per turn, then yield with a short narration so the user can interject. Do not chain long sequences without surfacing what you are doing.

Always observe before acting

Call app_control_observe before your first input action whenever the screen state matters (e.g. you need to know what is on screen, where a UI element is, or whether the app is even running). Re-observe after actions that may have moved the window or changed visibility.

observe waits a short settle delay (default ~200ms) before capturing so the target app and the WindowServer can flush pending input and composite a fresh frame. If the captured screenshot looks one input behind the latest state (common with emulators or other slow-feedback apps), pass a larger settle_ms. For static UIs where you just want a quick snapshot, pass settle_ms: 0 to skip the wait.

Input choice

• Prefer app_control_sequence over multiple back-to-back app_control_press

calls when sending an ordered batch of presses (e.g. menu navigation, repeated movement). Sequence runs in a single round-trip — the target app is activated once at the start and the keys are sent serially without any window for keyboard focus to drift to another app between presses. Each step may carry its own duration_ms (hold) and gap_ms (pause after).

• Prefer app_control_combo over rapid sequential app_control_press for

simultaneous inputs (e.g. cmd+shift+4). combo holds every key at once; sequential presses interleave key-down and key-up events.

• Use app_control_type for literal text into a focused field.

Coordinate caveat

app_control_click and app_control_drag use window-relative coordinates. The window may move or resize between observation and click — if you are uncertain whether the window has shifted, re-observe first.

App targeting

Use bundle IDs (e.g. com.example.app) when possible — they are the most reliable identifier. Fall back to localized process names if a bundle ID is unavailable.

Ending the session

Call app_control_stop when you are done. Do not auto-quit the controlled app — stop only ends the app-control session, leaving the app running.