Implementation:Microsoft Playwright CrDevTools

Knowledge Sources	Microsoft_Playwright
Domains	Chromium, DevTools
Last Updated	2026-02-12 00:00 GMT

Overview

Concrete tool for intercepting and persisting Chrome DevTools preferences via runtime bindings provided by the Playwright library.

Description

The `CRDevTools` class intercepts preferences-related DevTools embedder methods through a Chrome Runtime binding (`__pw_devtools__`) and stores preferences as a JSON file at a specified path in the browser installation directory. It supports `getPreferences`, `setPreference`, `removePreference`, and `clearPreferences` methods. The class lazily loads preferences from disk on first access and batches write operations through a promise chain (`_savePromise`) to avoid concurrent file writes. It also installs a JavaScript snippet into the DevTools page that overrides the `InspectorFrontendHost` methods to route through the binding.

Usage

Use CrDevTools when Playwright opens DevTools alongside an automated browser and needs to persist user preferences (like dark mode, panel layouts) across sessions.

Code Reference

Source Location

• Repository: Microsoft_Playwright
• File: packages/playwright-core/src/server/chromium/crDevTools.ts

Signature

export class CRDevTools {
  constructor(preferencesPath: string);
  install(session: CRSession): void;
}

Import

import { CRDevTools } from '../server/chromium/crDevTools';

I/O Contract

Inputs

Name	Type	Required	Description
preferencesPath	string	Yes	File system path where DevTools preferences are stored as JSON
session	CRSession	Yes	CDP session for the DevTools target

Outputs

Name	Type	Description
(side effect)	void	Installs runtime binding and overrides DevTools preference methods

Usage Examples

import { CRDevTools } from '../server/chromium/crDevTools';

const devtools = new CRDevTools('/path/to/browser/devtools-preferences.json');
devtools.install(devToolsSession);
// DevTools preferences will now be persisted to the specified file

Related Pages

• Environment:Microsoft_Playwright_Node_Runtime_Environment