HTTP Request Timing
Load a URL in headless Chromium and stream every fetched resource with size and timing.
Reports up to 400 resources. Hard wall-clock cap 50 s.
Cross-origin responses without a Timing-Allow-Origin header report size as 0 (browser limitation).
negotiated and refuses TLS 1.3. The cert chain itself is fine — this is a handshake-stack issue, not a verification one. Typical fingerprint: older Apache / IIS / Nginx with a modern Let's Encrypt cert grafted on, or a stale load balancer config. Modern Chrome's TLS 1.3 ClientHello (with post-quantum key share, ~1.5 KB) often fails against such servers; we launch Chromium with --disable-features=PostQuantumKyber here so the load can still complete via TLS 1.2.
Monitor this automatically
NetTests can run this check on a schedule, preserve historical results, compare changes over time, and alert you the moment something breaks.
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What does this tool measure?
It loads your URL in a real headless Chromium browser and records every network request the page triggers — HTML, CSS, JavaScript, images, API calls — along with its HTTP status, size, and timing. This gives you a realistic picture of what a visitor's browser actually loads, not just the server response.
How is this different from a simple ping or HTTP header check?
A ping only tests ICMP reachability. An HTTP header check fetches a single response. This tool runs a full browser load, following redirects, executing JavaScript, and fetching all sub-resources — so it catches slow third-party scripts, broken asset URLs, and render-blocking resources that simpler tools miss.
What causes a high total load time?
- Large unoptimised images or JavaScript bundles.
- Slow third-party scripts (analytics, chat widgets, ads).
- Many sequential requests (render-blocking CSS/JS).
- High server TTFB (Time to First Byte) — indicates slow origin or no caching.
- Uncompressed assets — enable gzip/Brotli on your server.
What does a non-200 status on a sub-resource mean?
A 404 on a CSS or JS file means the asset is missing — the page may render broken. A 5xx on an API call indicates a server error. 3xx redirects add latency. Each non-200 resource is highlighted in the results table.
Why does the page load differently here than in my browser?
The tool runs from this server's network location without cookies, cache, or login state. Performance differs due to geographic distance, missing session state, and the absence of browser cache. Use it to test cold-load from an external vantage point, not to reproduce a logged-in session.