grafana/k6 · critical

getting browser version information

Error message

getting browser version information: %w

What it means

fetchVersion calls Browser.getVersion over CDP right after connecting to fill protocol/product/user-agent info (used by Version()/UserAgent()). This error wraps that call failing, meaning the connection died immediately after the handshake or the endpoint is not behaving like a Chromium browser-level DevTools endpoint.

Solutions

1. Fetch http://host:port/json/version and use its webSocketDebuggerUrl verbatim — old session URLs are invalid
2. Confirm the browser process stays alive across the connect (check logs/exit code)
3. Verify the endpoint is a Chromium browser-level DevTools endpoint, not a page target or WebDriver endpoint
4. Match the Chromium/headless-shell version to what the k6 browser module supports

Example fix

# before
K6_BROWSER_WS_URL=ws://localhost:9222/devtools/page/abc123 k6 run s.js # page-level endpoint

# after
curl -s http://localhost:9222/json/version | jq -r .webSocketDebuggerUrl
K6_BROWSER_WS_URL=<browser-level url> k6 run s.js

// Preflight the remote DevTools endpoint and pin the fresh browser-level URL
const res = http.get(`${__ENV.K6_BROWSER_CDP}/json/version`);
if (res.status !== 200) throw new Error('CDP endpoint not serving /json/version');
const wsUrl = res.json('webSocketDebuggerUrl');
if (!wsUrl || !wsUrl.includes('/devtools/browser/'))
  throw new Error('webSocketDebuggerUrl is not a browser-level endpoint');
__ENV.K6_BROWSER_WS_URL = wsUrl;

try {
  browser.userAgent(); // triggers version fetch
} catch (e) {
  if (String(e).includes('getting browser version information')) {
    // refetch /json/version, relaunch with fresh URL, retry once
  }
}

When it happens

Trigger: The WS URL pointing at a page-level endpoint (/devtools/page/<id>) or non-browser service; a stale ws URL from a previous browser session; the browser process crashing or the proxy dropping the session right after connect.

Common situations: K6_BROWSER_WS_URL copied from an old run or pointing at Chrome's HTTP port instead of the webSocketDebuggerUrl; browserless/CDP proxies terminating sessions; protocol version mismatch with unusual Chromium builds.

Related errors

• internal error while auto-attaching to browser pages
• internal error while getting browser target info
• adding init script to browser context
• can't fetch the page for unknown reason
• cannot set cookies

AI-assisted analysis of grafana/k6@3fcf5388d7 (2026-08-18). Data as JSON: /api/errors/723f7b2cc6bff4ba. Report an issue: GitHub.

Appendix: source

Thrown at internal/js/modules/k6/browser/common/browser.go:807

	product := b.version.product
	_, after, ok := strings.Cut(product, "/")
	if !ok {
		return product
	}
	return after
}

// fetchVersion returns the browser version information.
func (b *Browser) fetchVersion() (browserVersion, error) {
	var (
		bv  browserVersion
		err error
	)
	bv.protocolVersion, bv.product, bv.revision, bv.userAgent, bv.jsVersion, err = cdpbrowser.
		GetVersion().
		Do(cdp.WithExecutor(b.vuCtx, b.conn))
	if err != nil {
		return browserVersion{}, fmt.Errorf("getting browser version information: %w", err)
	}

	// Adjust the user agent to remove the headless part.
	//
	// Including Headless might cause issues with some websites that treat headless
	// browsers differently. Later on, [BrowserContext] will set the user agent to
	// this user agent if not set by the user. This will force [FrameSession] to
	// set the user agent to the browser's user agent.
	//
	// Doing this here provides a consistent user agent across all browser contexts.
	// Also, it makes it consistent to query the user agent from the browser.
	if b.browserOpts.Headless {
		bv.userAgent = strings.ReplaceAll(bv.userAgent, "Headless", "")
	}

	return bv, nil
}

View on GitHub (pinned to 3fcf5388d7)