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  1. Home
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  3. HTTP protocol checker
Your files stay on your device

HTTP protocol checker

Show which HTTP version a probe negotiates for a URL and whether Alt-Svc advertises HTTP/3, with QUIC marked not tested.

This tool is in beta

Still being tested. If a result looks wrong, tell us.

Report a problem

Press the button to check the protocol

Nothing leaves this page until you do. Type the full address, scheme included.

Honest limits, stated up front. The probe lanes do not surface the connection's negotiated protocol (ALPN), so this tool reports the negotiated version as not surfaced rather than guessing from headers. QUIC is marked Not Tested: no lane here dials UDP, so an h3 advertisement is evidence of advertising, never proof of a working HTTP/3 connection. For the version your own browser negotiates, open the site's DevTools protocol column.

URL

Up to 2,048 characters

The URL is probed with GET, following redirects up to 10 so the answer comes from the page the URL lands on. The Alt-Svc response header is read for an HTTP/3 advertisement.

What leaves your browser

The URL you type is fetched through this project's capped proxy server (GET only, public hosts only, size and time caps, rate-limited), because a browser cannot read another origin's response headers itself. This page leaves your browser only when you press the button; never on load, never in the background. Nothing is sent anywhere else. Google Analytics still measures the visit to this page, and it never receives what you run through this tool.

More network tools

  • HTTP timing probe
All network tools

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