Web (Chrome DevTools Protocol)

Overview

The web adapter captures web page accessibility trees via the Chrome DevTools Protocol (CDP). This works with Chrome, Chromium, and Chromium-based browsers (Edge, Brave, etc.).

Requirements

Chrome or Chromium-based browser
Browser must be started with --remote-debugging-port flag

Setup

Start Chrome with remote debugging

# macOS
/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --remote-debugging-port=9222

# Windows
chrome.exe --remote-debugging-port=9222

# Linux
google-chrome --remote-debugging-port=9222

Install with web extra

pip install computeruseprotocol[web]

npm install computeruseprotocol
# Web adapter is included by default

Capture

# Python
python -m cup --platform web --cdp-port 9222

# TypeScript
npx cup --platform web --cdp-port 9222

The web adapter connects to Chrome's DevTools WebSocket endpoint, enables the Accessibility domain, and retrieves the full ARIA accessibility tree. It then maps ARIA roles directly to CUP roles (they share the same vocabulary).

Role mapping

Web ARIA roles map 1:1 to CUP roles since CUP's role taxonomy is ARIA-derived:

ARIA Role	CUP Role
`button`	`button`
`checkbox`	`checkbox`
`combobox`	`combobox`
`textbox`	`textbox`
`link`	`link`
`img`	`img`
`list`	`list`
`listitem`	`listitem`
`dialog`	`dialog`
`tab`	`tab`
(etc.)	(same)

Action mapping

CUP Action	Web (CDP) Implementation
`click`	`Input.dispatchMouseEvent` at element center
`type`	`DOM.focus` + `Input.insertText`
`setvalue`	`Runtime.callFunctionOn` to set `.value`
`toggle`	`DOM.focus` + click
`expand` / `collapse`	Click
`select`	`DOM.focus` + click
`scroll`	`Input.dispatchMouseEvent` with `mouseWheel` type

Platform-specific properties

For the full platform-specific property schema, see Node Structure.

The web adapter captures CSS selectors and XPaths in platform.web, useful for hybrid automation approaches.

Limitations

Requires Chrome to be started with --remote-debugging-port
Only captures the active tab by default
Shadow DOM elements may have limited accessibility tree representation