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HowFastly
Binary Cache:
- Cache: https://cache.ysun.co
- Key:
cache.ysun.co-1:WxPYwT5g3kt9XhUhHPpNLZKI9HIOsVVAuqSHpok8Qt4=
HowFastly measures your connection speed to the Fastly network, inspired by speed.cloudflare.com. People keep asking for a Fastly equivalent, and fastly-debug.com reports connectivity diagnostics rather than throughput.
This tool runs as a Fastly Compute instance (wasm32-wasip1) and streams test payloads, latency pings, and serves the Leptos web UI, built to showcase the flexibility of the Compute platform.
- Web: https://speed.edgecompute.app (or https://howfastly.edgecompute.app)
- CLI:
nix run github:stepbrobd/howfastly#howfastly
The CLI probes HTTP/3, which reqwest still gates behind an unstable cfg, so a crates.io install needs the flag that the flake sets for you:
RUSTFLAGS='--cfg reqwest_unstable'
For Nix users: cache.nixos.org and cache.ysun.co are both fronted by Fastly, so these numbers are a fairly accurate representation of how fast binary cache fetches will run on your connection.
Methodology (following Cloudflare's):
- 25 unloaded latency pings (median, jitter, min, avg)
- Download and upload transfers from 100 kB to 100 MB, size classes interleaved so both directions show estimates early
- Per size iteration counts (8/8/6/4/2), larger transfers have lower relative variance and need fewer repeats
- p90 headline speed, per size medians and box plots, loaded latency per direction (bufferbloat)
- 30s time budget per direction, roughly 640 MB transferred worst case
- Server processing time is subtracted from every sample via Server-Timing
For CLI:
nix run github:stepbrobd/howfastly#howfastly
howfastly follows cfspeedtest
flags, see --help.
Planned:
- HTTP/3. All measurements are currently on TCP (HTTP/2 in browsers, HTTP/1.1 in
CLI). The Fastly edge already terminates HTTP/3 for this service
(
curl --http3-onlygets a 200), but neither an Alt-Svc header nor an HTTPS DNS record advertises it, so no real client can use QUIC. Nix recently added HTTP/3 support in NixOS/nix#15961 by me ;) and both caches already uses it, so TCP-only results are not representative of h3 cache fetches.
Sponsorship disclaimer
Not an official Fastly product or project. This project is generously supported by Fastly through the Fast Forward program. The views and content of this project are solely those of the author and do not imply endorsement by Fastly.