app_eval

This tool on every surface: CLI · MCP · Python · JavaScript · Go · Java · .NET

Run a JavaScript expression in the current WebView and return its value as a string. Needs a WebView context — switch with app_context first. Objects come back as JSON. This is the escape hatch for anything app_map and app_text do not cover, and the way to ask a page a question directly rather than inferring the answer from what is on screen.

Changes the device, the app or the session: readOnlyHint is false.

Arguments

Name	Type	Required	What it is
device	string		Device serial to target, e.g. "emulator-5554". Omit when only one device is running.
driver	string: uiautomator2, uiautomator, wda		Driver to use: "uiautomator2" (default for Android; fast, installs a server APK on first use), "uiautomator" (Android, installs nothing, slower, cannot type), or "wda" (WebDriverAgent: iOS simulators and iPhones).
expression	string	yes	A JavaScript expression, e.g. "document.title".

Examples

Each is the arguments of a tools/call request; the first is shown whole.

Read the page title in a WebView

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "app_eval",
    "arguments": {
      "expression": "document.title"
    }
  }
}

On a device

mobium eval document.title on an Android 15 emulator