Judge whether a video call will hold up
Look at latency and jitter first, then whether the up and down rates can carry the picture.
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Guide
The speed test uses the public https://speed.cloudflare.com endpoint directly. The latency stage issues repeated __down?bytes=0 requests, discards the first connection as a warm-up and takes the smallest RTT, estimating jitter from the mean difference between adjacent samples; download and upload then step up through tiers of increasing data size.
Updated 2026-09-272 min read
| Stage | Actual network traffic |
|---|---|
| Latency | 9 × GET /__down?bytes=0, with the first sample only a warm-up |
| Download | 1 MB → 10 MB → 25 MB → 100 MB, possibly ending early depending on speed |
| Upload | 1 MB → 5 MB → 25 MB POSTed to /__up, possibly ending early depending on speed |
Look at latency and jitter first, then whether the up and down rates can carry the picture.
Measure once in each configuration at the same spot and compare the link behaviour.
Read the sample taken about every 200 ms to judge whether the link is stable.
No. The POST data is a random binary payload generated on the spot by the page.
The test connects directly to Cloudflare, so Cloudflare can see the usual network request information and your exit IP and receives the random test payload; the page never uploads your files or text. Do not run it without permission on a network that bills for traffic or forbids speed testing.
Updated 2026-09-27
Measure latency, jitter, download and upload with a live speed curve and use-case ratings
A test uses up to about 170 MB of traffic, so be careful on mobile data
The test service is provided by Cloudflare and takes about 15-40 seconds
The test connects directly to Cloudflare's global nodes, so the result reflects the link quality between you and that node; a proxy / VPN, browser throttling or a weak Wi-Fi signal will all affect it. On slow networks the larger file sizes are skipped automatically to save traffic.