Download Test

What to test here

This page offers binary files of different sizes for download. Different browsers and HTTP clients like curl, as well as intermediate SSE security gateways, may show quite different download speeds depending on protocol. See Speed of H3 for background.

Click Fetch & Verify to measure download throughput and verify content integrity directly in your browser, or use the curl command in the table to trigger the download from a shell. An SHA-256 checksum is listed for each file — any modification or truncation introduced by a gateway will be detected. On a mismatch, the browser function scans block-by-block to identify exactly where the content diverged. The file structure that makes this possible is described in the section below.

To compare throughput across protocols, fetch the same file over different hostnames — for example https://h2.sse-testcenter.org/download/1m.bin vs. https://h3.sse-testcenter.org/download/1m.bin — or use the Hosts page to navigate to a specific protocol host and run the download from there. The protocol widget in the header shows what protocol your current connection is using.

Structured binary files

Each file consists of consecutive SHA-256 block hashes: block i contains the 32-byte SHA-256 digest of the 4-byte big-endian encoding of i. The content is incompressible and fully deterministic — any byte can be verified without storing a reference copy.

curl -o /dev/null -w "%{speed_download} B/s\n" https://sse-testcenter.org/download/1k.bin

curl -o /dev/null -w "%{speed_download} B/s\n" https://sse-testcenter.org/download/100k.bin

curl -o /dev/null -w "%{speed_download} B/s\n" https://sse-testcenter.org/download/1m.bin

curl -o /dev/null -w "%{speed_download} B/s\n" https://sse-testcenter.org/download/10m.bin