microsoft/playwright · error · Error

Cannot use --mobile together with --device, pick one.

Error message

Cannot use --mobile together with --device, pick one.

What it means

Thrown by configFromCLIOptions() when both --mobile and --device are supplied. --mobile is a shorthand that auto-selects a device preset ('iPhone 17' for webkit, 'Pixel 10' otherwise), so it is mutually exclusive with an explicit --device name. The guard prevents two sources of device-emulation configuration from contradicting each other.

Source

Thrown at packages/playwright-core/src/tools/mcp/config.ts:309

function configFromCLIOptions(cliOptions: CLIOptions): Config & { configFile?: string } {
  const { browserName, channel } = resolveBrowserParam(cliOptions.browser);

  // Launch options
  const launchOptions: playwrightTypes.LaunchOptions = {
    channel,
    executablePath: cliOptions.executablePath,
    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;

View on GitHub (pinned to c8fc3bf8d3)

Solutions

1. Remove one of the two flags. Keep --device if you want a specific Playwright device descriptor, or --mobile if you want the auto-selected default preset.
2. If flags come from a config file or environment, audit that file for both keys being set and remove one.
3. Check any wrapper script or alias that appends flags automatically.

Example fix

// before
playwright mcp --mobile --device "iPhone 15"
// after (explicit device)
playwright mcp --device "iPhone 15"
// after (auto mobile preset)
playwright mcp --mobile

if (cliOptions.mobile && cliOptions.device) {
  throw new Error('Choose either --mobile or --device, not both.');
}

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

When it happens

Trigger: Invoking the MCP CLI with both flags set, e.g. `--mobile --device "iPhone 15"`. Also reachable from a config file or env that populates both cliOptions.mobile and cliOptions.device.

Common situations: Copy-pasted flags from an example that used --device into a command that already had --mobile; migration from --device to --mobile without removing the old flag; a wrapper script that sets both unconditionally.

Related errors

• --mobile is not supported with the Firefox browser.
• Device emulation is not supported with cdpEndpoint.
• 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/9700a4ab2116e688. Report an issue: GitHub.