Chrome DevTools Access

When the DOM and fetch are not enough, a script you have installed can use the Chrome DevTools Protocol (CDP) on the pages it matches: read network responses including cross-origin iframes, send genuinely-trusted input to canvas apps that ignore synthetic events, rewrite requests mid-flight, set breakpoints, or capture full-page screenshots. You or your AI agent build the script; Customaise exposes the capability and gates it.

Turning it on, and the safety model

Installing a script that declares the grant does not give it access. You enable the capability yourself, per session, under Settings, Scripts, Chrome DevTools Access. It is off by default and resets every Chrome restart. A script must declare @grant CM_devtools and a written @devtools-justification you can read before installing. Chrome shows its own yellow banner while a session is held, one switch ends every session at once, and every session is recorded to a local audit log on your device. Marketplace scripts that use it are reviewed before they are listed.

Building one

Declare the grant and justification in the metadata header, then acquire a session with CM_devtools(), do your work, and release it; the scoped helper CM_withDevtools() acquires and releases for you even if your code throws. CDP method names come from the official Chrome DevTools Protocol reference. Customaise ships the full reference to your AI agent over MCP, so Cursor, Claude Code, Codex, and other connected agents already know the grant, the lifecycle, and the error codes; describe what you want and let the agent build the script.

Screenshots of any tab

The same Chrome debugger that powers CM_devtools also powers screenshots. An AI agent can capture any open tab, not only the one in front, and return a full-page image of the whole scrollable page without pulling a background tab to the front or taking your focus.