Measures your connection against Cloudflare's speed-test endpoints (the same ones speed.cloudflare.com uses, CORS-enabled): a best-of-three latency probe, a warm-up, then download phases that escalate from 1 MB while the Worker's 4-second budget allows — a phase that runs out of time is cut short but its bytes still count — and a bounded upload of random bytes. Throughput is reported per phase and as a peak in Mbps with a plain-language verdict. Because the Worker stops at 5 seconds and uses one connection, treat the result as a floor for sustained multi-connection tests, especially on very fast links. No account, no cookies; Cloudflare sees your IP as with any request.