throttlecheck

Your speed test says 400 Mbps. So why does Netflix buffer? Speed tests measure the one server your ISP knows you're testing with. throttlecheck downloads from Netflix's own video servers, a public video stream and the big download CDNs, side by side with a neutral control, and shows you which ones your internet provider is holding back.

uvx throttlecheck

_{Demo with made-up results, generated by docs/demo.py.}

What it tests

Each one gets 4 parallel downloads for 8 seconds; the first 1.5 seconds are ignored while connections speed up. The control runs first and last, and the faster of the two is the baseline.

How it decides

• Looks throttled: under 25% of the control, or under 60% and flat. A rate limiter holds speed at one number (mobile carriers like 1.5, 3 or 5 Mbps for video); a busy network goes up and down.
• Slower: under 60% of the control without the flat line. Could be throttling, could just be a server further away.
• Normal: everything else.

Throttling is usually by time of day or by plan, so run it a few times, including at busy evening hours, before calling your ISP. Mobile hotspots and "unlimited" phone plans are where you're most likely to see it.

Options

throttlecheck                       # everything
throttlecheck --only netflix        # control + Netflix
throttlecheck --seconds 15          # longer, steadier measurements
throttlecheck --streams 8           # more parallel connections (fast fiber)
throttlecheck --json                # for scripts and cron

A full run downloads a few hundred megabytes on a fast connection; mind your data cap on mobile.

Install

uvx throttlecheck           # run without installing
pipx install throttlecheck  # or install it

Requires Python 3.9+. The only dependency is rich. macOS, Linux and Windows.

License

MIT