HTTP/3 & QUIC Checker 作成者: AMZLY

HTTP/3 & QUIC Checker — instantly see which HTTP version any website uses

HTTP/3 & QUIC Checker tells you at a glance whether the website you're currently visiting is served over the modern HTTP/3 protocol with QUIC — or still relies on older HTTP/2 or HTTP/1.1. No configuration, no clutter: the answer is right there in your toolbar icon.

What the icon tells you

The toolbar icon shows the site's HTTP version as a colored number, so you get the result without even clicking:

• Green "3" — The site supports HTTP/3 / QUIC. Either the page was actually loaded over HTTP/3, or the server advertises HTTP/3 via its alt-svc header (your browser will switch to it on the next visit).
• Yellow "2" — The site uses HTTP/2, but no HTTP/3 / QUIC.
• Grey "1" — The site uses only HTTP/1.1.
• Grey "?" — No data available yet (for example on internal browser pages). Just reload the page.

Click for the details

Click the icon and a small popup opens with the result in plain language — including which protocol was actually used for the current page (e.g. h3, h2, http/1.1). Perfect for a quick sanity check while browsing.

How it works

Detection happens entirely locally in your browser, using two reliable signals:

1. The alt-svc response header, which reveals whether the server offers HTTP/3 (QUIC).
2. The protocol actually negotiated for the page (via the browser's own navigation timing / nextHopProtocol).

Because browsers often only upgrade to HTTP/3 on the second visit to a site (after learning about it via alt-svc the first time), the extension correctly shows green even when the first load still used HTTP/2.

Who it's for

• Web developers & DevOps verifying that HTTP/3 / QUIC is correctly deployed on their servers or CDNs.
• Sysadmins & performance engineers auditing sites and infrastructure.
• Curious users & students who want to understand how the modern web is delivered.

Privacy first

This extension does not collect, store, or transmit any personal data. All protocol analysis is performed locally in your browser and never leaves your device. No tracking, no analytics, no external servers.

Available in 33 languages

The interface adapts automatically to your browser language, with full support for: English, German, French, Spanish, Italian, Dutch, Polish, Portuguese (Brazil & Portugal), Japanese, Turkish, Russian, Ukrainian, Chinese (Simplified & Traditional), Korean, Vietnamese, Indonesian, Thai, Arabic, Hebrew, Hindi, Tamil, Bengali, Swedish, Finnish, Danish, Norwegian, Czech, Slovak, Romanian, Hungarian and Greek. Right-to-left languages (Arabic, Hebrew) are displayed in proper RTL layout.

Lightweight & open

Fast, tiny, and built on Manifest V3. It only reads the information it needs to identify the protocol — nothing more. If you find it useful, there's an optional way to support development right from the popup.

Install it, open any website, and watch the number in your toolbar.