Failed to fetch CDP version info from ${versionUrl}: ${respo

Error message

Failed to fetch CDP version info from ${versionUrl}: ${response.status} ${response.statusText}

What it means

resolveCdpWebSocketUrl fetches the Chrome DevTools Protocol /json/version endpoint to discover the browser's webSocketDebuggerUrl. If the HTTP response is not OK (non-2xx), the library throws with the target URL and status/statusText. This means the CDP endpoint was reachable enough to answer but rejected the request or reported an error.

Source

Thrown at browser/firecrawl/src/resolve-cdp.ts:25

): Promise<string> {
  if (url.startsWith('ws://') || url.startsWith('wss://')) {
    return url;
  }

  if (url.startsWith('http://') || url.startsWith('https://')) {
    const baseUrl = url.replace(/\/$/, '');
    const versionUrl = `${baseUrl}/json/version`;

    logger?.debug?.(`Resolving WebSocket URL from ${versionUrl}`);

    const controller = new AbortController();
    const timeoutId = setTimeout(() => controller.abort(), 10000);

    try {
      const response = await fetch(versionUrl, { signal: controller.signal });

      if (!response.ok) {
        throw new Error(
          `Failed to fetch CDP version info from ${versionUrl}: ${response.status} ${response.statusText}`,
        );
      }

      const data = (await response.json()) as { webSocketDebuggerUrl?: string };
      if (!data.webSocketDebuggerUrl) {
        throw new Error(`No webSocketDebuggerUrl found in CDP version response from ${versionUrl}`);
      }

      logger?.debug?.(`Resolved WebSocket URL: ${data.webSocketDebuggerUrl}`);
      return data.webSocketDebuggerUrl;
    } catch (error) {
      if (error instanceof Error && error.name === 'AbortError') {
        throw new Error(`Timeout resolving WebSocket URL from ${versionUrl} (10s)`);
      }
      throw error;
    } finally {
      clearTimeout(timeoutId);

View on GitHub (pinned to 75dd419e61)

Solutions

Check the response status in the error: 401/403 means auth, 404/410 means the session is gone — create a new browser session
Verify the Firecrawl API key and apiUrl configuration
Retry the connection; if the remote browser was torn down, launch a fresh FirecrawlBrowser
Check network/proxy interference with the versionUrl

Defensive patterns

Strategy: retry

Validate before calling

const res = await fetch(versionUrl);
if (!res.ok) console.error('CDP endpoint unhealthy:', res.status, await res.text());

Try / catch

try {
  const browser = new FirecrawlBrowser(config);
} catch (e) {
  if (e instanceof Error && e.message.includes('Failed to fetch CDP version info')) {
    // status embedded in message; 401/403 = auth, 404/410 = recreate session
    await recreateBrowserSession();
  } else throw e;
}

Prevention

Pre-flight check the /json/version endpoint before constructing the browser
Rotate API keys before expiry; treat 401/403 as auth, 404 as dead session
Recreate browser sessions instead of reusing long-lived CDP URLs
Log response bodies on failure to distinguish proxy vs CDP errors

When it happens

Trigger: Calling new FirecrawlBrowser(...) or accessing the browser's wsUrl when the Firecrawl-provided CDP versionUrl responds with an HTTP error status (401, 403, 404, 500, 502, etc.).

Common situations: Expired or invalid Firecrawl API key embedded in the URL; wrong or stale CDP endpoint (browser session already terminated); proxy/gateway errors between client and remote browser; misconfigured apiUrl.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/f8afaec1e6b22e4a. Report an issue: GitHub.