Methodology

How we measure website performance

What we measure

  • TTFB Time to First Byte — how long until the server starts sending a response. This is the primary speed metric we rank by. Lower is better.
  • Total time Total elapsed time for the HTTP response to complete, including all headers and body content received.
  • Uptime % Percentage of checks where the site returned a successful HTTP response (2xx or 3xx status code) within the timeout window.

How we measure

Each check is an HTTPS GET request made by a Cloudflare Worker to the domain's root URL (https://domain.com/). We follow up to one redirect.

Timeout 10 seconds. Requests that don't complete within 10s are recorded as failed (is_up = false).
Infrastructure Cloudflare Workers — globally distributed edge compute. Requests originate from Cloudflare's edge network.
Frequency Every domain is checked approximately every 30 minutes, on a rotating schedule across the full S&P 500 list.

What we don't measure

  • Full page render time (no browser, no JavaScript execution)
  • DNS resolution time (not broken out separately)
  • CDN cache hit/miss status
  • Asset load times (images, CSS, JS files)
  • Mobile vs. desktop performance
  • Geographic variation (single Cloudflare edge region per check)
  • Core Web Vitals (LCP, CLS, FID)

Limitations & caveats

Bot blocking: Some companies detect and block automated requests. A site appearing "down" may simply be blocking our monitor rather than being genuinely unavailable. We can't distinguish between these cases.

CDN caching: Many large sites serve cached responses from CDN edge nodes, which may appear faster than their actual origin server performance.

Redirects: If a domain redirects to a different URL (e.g., www. subdomain), the redirect time is included in our measurement.

Single region: Currently all checks originate from a single Cloudflare region. Companies with stronger East Coast vs. West Coast infrastructure may appear faster or slower depending on routing.

S&P 500 inclusion: We use the S&P 500 constituent list at the time of our data collection. Companies added or removed from the index may lag behind real-time changes.

Future plans

  • Multi-region checks (US East, US West, Europe, Asia)
  • DNS resolution timing broken out separately
  • Historical trend data over weeks and months
  • Public API for accessing raw data
  • Alerting / status subscriptions