microsoft/playwright · error · Error

Device emulation is not supported with cdpEndpoint.

Error message

Device emulation is not supported with cdpEndpoint.

What it means

Thrown by configFromCLIOptions() when a device preset is active (either --device or --mobile) and --cdpEndpoint is also set. Device emulation is applied as context options on a freshly created context, but a CDP endpoint connects to an already-running browser whose context Playwright does not own, so the emulation options cannot be honored reliably.

Source

Thrown at packages/playwright-core/src/tools/mcp/config.ts:316

    headless: cliOptions.headless,
  };

  // --sandbox was passed, enable the sandbox
  // --no-sandbox was passed, disable the sandbox
  if (cliOptions.sandbox !== undefined)
    launchOptions.chromiumSandbox = cliOptions.sandbox;

  let device = cliOptions.device;
  if (cliOptions.mobile) {
    if (device)
      throw new Error('Cannot use --mobile together with --device, pick one.');
    if (browserName === 'firefox')
      throw new Error('--mobile is not supported with the Firefox browser.');
    device = browserName === 'webkit' ? 'iPhone 17' : 'Pixel 10';
  }

  if (device && cliOptions.cdpEndpoint)
    throw new Error('Device emulation is not supported with cdpEndpoint.');

  // Context options
  const contextOptions: playwrightTypes.BrowserContextOptions = device ? playwright.devices[device] : {};

  if (cliOptions.proxyServer) {
    const proxy: playwrightTypes.LaunchOptions['proxy'] = { server: cliOptions.proxyServer };
    if (cliOptions.proxyBypass)
      proxy.bypass = cliOptions.proxyBypass;
    // Set on both to ensure CLI takes precedence over any proxy set in the config file
    // (launchOptions.proxy applies at browser launch, contextOptions.proxy at context creation).
    launchOptions.proxy = proxy;
    contextOptions.proxy = proxy;
  }

  if (cliOptions.storageState)
    contextOptions.storageState = cliOptions.storageState;

  if (cliOptions.userAgent)

View on GitHub (pinned to c8fc3bf8d3)

Solutions

1. Drop --device/--mobile when connecting via --cdp-endpoint, and configure emulation inside the target browser instead.
2. If you need device emulation, remove --cdp-endpoint so Playwright launches and owns the browser context.
3. If both are required, launch a browser with the device profile locally and expose its CDP endpoint yourself, then connect without --device.

Example fix

// before
playwright mcp --device "Pixel 10" --cdp-endpoint ws://localhost:9222
// after (own the browser)
playwright mcp --device "Pixel 10"
// after (use existing browser, no emulation)
playwright mcp --cdp-endpoint ws://localhost:9222

if ((cliOptions.device || cliOptions.mobile) && cliOptions.cdpEndpoint) {
  throw new Error('Device emulation cannot be combined with --cdp-endpoint.');
}

function deviceEmulationActive(opts: { device?: string; mobile?: boolean }): boolean {
  return Boolean(opts.device) || Boolean(opts.mobile);
}

When it happens

Trigger: Combining `--device "Pixel 10" --cdp-endpoint ws://host:9222` or `--mobile --cdp-endpoint ...` on the MCP CLI.

Common situations: Wanting to drive an existing Chrome instance (e.g. for debugging or a pre-launched browser) while also wanting mobile emulation; leftover --device from a previous run combined with a new --cdp-endpoint.

Related errors

• Cannot use --mobile together with --device, pick one.
• --mobile is not supported with the Firefox browser.
• Invalid resolution format: use ${name}="800x600"
• Invalid ${name}: ${value}. Valid values are: ${options.join(
• Init script file does not exist: ${script}

AI-assisted analysis of microsoft/playwright@c8fc3bf8d3 (2026-08-12). Data as JSON: /api/errors/2164586497491412. Report an issue: GitHub.