QPACK header compression
Your browser sends a bunch of headers with every request. HTTP/2 compresses them with HPACK; HTTP/3 uses QPACK. Both maintain a dynamic table — headers seen before get compressed to a tiny index reference on the second request. Click the buttons to see it happen live with your own headers.
Your browser isn't using HTTP/3 on this connection — the demo still works, but the QPACK column shows what HTTP/3 would cost.
raw headers
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HPACK (h2)
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QPACK (h3)
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Request #: your repeated headers now cost of request #1 — the dynamic table at work.
Cumulative header bytes across requests
Show field-by-field breakdown
| header | raw | HPACK | QPACK | how |
|---|
These are re-encodings of the headers your browser really sent — computed server-side with both encoders on identical input. They are not bytes sniffed off the wire; the live HTTP/3 connection does its own QPACK.