Phone Use

Overview

You can see and control the Android screen through three channels:

• The UI tree — screen_operation_accessibility reads the semantic tree (text, labels, bounds, clickability) and acts on nodes by token.
• Pixels — screenshot captures the screen as an image and view_image reads image files, so you can visually inspect any app.
• Coordinates — screen_operation_shell injects tap/swipe/key events at screen-pixel coordinates.

Use the tree first; drop to pixels and coordinates when the tree cannot see or reach the target. Coordinates may come from node bounds or from a screenshot — compute them, never guess.

First-use consent: when the accessibility or overlay permission is missing, the first screen tool call asks the user to grant both. If the user declines, the tool fails with a consent message — tell the user what to enable and stop; do not retry in a loop. Root is not required; it only shortens the permission chain.

Workflow

1. Open the target

Prefer open_uri when a deep link lands closer to the goal than the launcher activity (e.g. a map at coordinates, a settings page). Otherwise resolve with find_installed_apps if the name is ambiguous, then launch_app.

2. Read the screen

Start with screen_operation_accessibility(operation: "read"). If the tree is empty or root-only, the app uses a non-native UI (Flutter, Unity, WebView, self-drawn canvas) — the tree will not work for this app. Do not retry the read. Instead switch to screenshot + coordinate operations via screen_operation_shell.

3. Act

• Tree shows a labeled, clickable node → tap it by token.
• Target is unlabeled, a bare container, or the node's bounds look misaligned with what you see → take a screenshot, locate the real target visually, convert image coordinates to screen pixels (see below), and tap with screen_operation_shell.
• set_text needs the accessibility method; there is no shell fallback for typing.

Image → screen coordinates. The screenshot is downscaled; its width/height in the result are the image's, not the screen's. Screen dimensions are in the tree header. Scale per axis: screen_x = image_x * screen_w / image_w (same for y).

4. Verify

Write operations return the updated tree automatically. Check that the UI actually reached the expected state — a success status means the event was injected, not that the app reacted. If the screen did not change as expected, re-examine: the target may be self-drawn (bounds unreliable — see §3), the tap may have landed on an overlay, or the app may need more time (wait_ms). On SHELL_TIMEOUT or SHELL_SESSION_LOST, verify the screen before retrying as the action may have partially executed.

5. Scroll

Scroll lists with screen_operation_shell(operation: "swipe", ...) — accessibility scroll steps are app-defined and unreliable. Derive coordinates from the scrollable container's bounds, swiping ~70% of the container. Start the gesture mid-container, not at the bottom edge: bottom-docked bars (tab bars, mini-players, toolbars) steal the touch-down. If a dock's bounds contain the start point, move the start above its top edge.

6. Navigate

Use key events via screen_operation_shell: Back (code: 4), Home (code: 3), Recents (code: 187).

Scrolling heuristics

• Before scrolling a list, define the exit condition in observable UI: a result count, an empty state, a section boundary.
• After two separate swipes the visible items are unchanged and nothing is loading → the list boundary is reached. Retarget once in case the gesture missed the container before concluding.
• One swipe per decision when hunting a specific item; batching 2–3 swipes is acceptable only when skipping intermediate states cannot miss the target.

App traps

When an unexpected result reveals a stable, verified rule about an app's UI, save it with memory (one natural-language sentence naming the app, the misleading element, and the correct action). Do not memorize temporary state, the current tab, or unverified guesses.