microsoft/playwright · error · Error

Connecting to workers is only supported in Chromium.

Error message

Connecting to workers is only supported in Chromium.

What it means

Thrown by BrowserType._connectToWorker() when the BrowserType name is not chromium. Worker (service worker / web worker) target attachment via CDP is a Chromium-only feature, so firefox/webkit are rejected up front.

Source

Thrown at packages/playwright-core/src/client/browserType.ts:186

      slowMo: params.slowMo,
      isLocal: params.isLocal,
      noDefaults: params.noDefaults,
      artifactsDir: params.artifactsDir,
    }, new TimeoutSettings().timeout(params));
    return await this._browserFromConnectResult(result);
  }

  private async _browserFromConnectResult(result: { browser: channels.BrowserChannel, defaultContext?: channels.BrowserContextChannel }): Promise<Browser> {
    const browser = Browser.from(result.browser);
    browser._connectToBrowserType(this, {}, undefined);
    if (result.defaultContext)
      await this._instrumentation.runAfterCreateBrowserContext(BrowserContext.from(result.defaultContext));
    return browser;
  }

  async _connectToWorker(endpoint: string, options: { timeout?: number } = {}): Promise<Worker>  {
    if (this.name() !== 'chromium')
      throw new Error('Connecting to workers is only supported in Chromium.');
    const result = await this._channel.connectToWorker({
      endpoint,
    }, new TimeoutSettings().timeout(options));
    return Worker.from(result.worker);
  }
}

function isConnectionTransport(value: any): value is api.ConnectOverCDPTransport {
  return !!value && typeof value === 'object' && typeof value.send === 'function' && typeof value.close === 'function';
}

View on GitHub (pinned to c8fc3bf8d3)

Solutions

1. Restrict worker attachment to chromium.
2. For non-chromium engines, attach at page level only (no worker targets).
3. Branch on browserType.name() === 'chromium' before calling _connectToWorker.

Example fix

// before
await browserType._connectToWorker(endpoint);
// after
if (browserType.name() === 'chromium')
  await browserType._connectToWorker(endpoint);

if (browserType.name() !== 'chromium')
  throw new Error('Worker attachment is chromium-only.');

function supportsWorkerConnect(bt: any): boolean {
  return bt?.name?.() === 'chromium';
}

When it happens

Trigger: Calling the internal `_connectToWorker(endpoint)` on firefox or webkit. This is an internal method exercised by tooling/CDP integrations that attach to worker targets.

Common situations: Custom tooling that abstracts over all BrowserTypes and tries worker attachment uniformly; experimental integrations ported from chromium to other engines.

Related errors

• Connecting over CDP is only supported in Chromium and WebKit
• Root session cannot be closed
• Cannot disconnect from this worker
• page: expected Page or Frame
• Passing a ConnectionTransport to connectOverCDP is not suppo

AI-assisted analysis of microsoft/playwright@c8fc3bf8d3 (2026-08-12). Data as JSON: /api/errors/ddf71ea6732790aa. Report an issue: GitHub.