HTTP/2, HTTP/3 and ALPN checker

Check supported HTTP versions, TLS ALPN negotiation, HTTP/1.1 fallback, QUIC hints and server configuration issues.

Options

Host or URLPort

Timeout

Probe HTTP/3 when this server supports it

Check HTTP/2, HTTP/3 and ALPN online

Enter a domain to test HTTPS protocol negotiation: ALPN, HTTP/2, HTTP/1.1 fallback, HTTP/3 probing and Alt-Svc headers.

The report helps spot server configuration gaps such as missing h2 in ALPN, missing HTTP/3 advertisement or a broken fallback path for older clients.

✓ The tool runs directly in the browser and is ready for quick checks without installing software.

✓ Input can be cleared and recalculated immediately, which is useful for repeated small tasks.

✓ Use fullscreen mode when you need more space for long text, structured data or large result blocks.

✓ Copy buttons are available on generated output so results can be reused in code, documents or support chats.

✓ Most operations are deterministic: the same input and options produce the same output.

✓ For sensitive content, prefer local browser tools and review the result before sharing it further.

Other Tools

HTTP Response Checker Online

Page loading speed checker

SSL/TLS test online

MX Toolbox online

Redirect checker online

DMARC, SPF, DKIM and BIMI checker online

User reviews

Reviews are checked before publication. We publish genuine positive feedback and specific criticism. Spam and insults without useful detail are not published; profanity and personal details are masked. Positive votes are counted immediately; negative votes are counted after review.

Reviews reflect users’ experiences, not a guarantee of results or a description of the service limits. Use the rating buttons above to leave a review.

No published reviews in this language yet.

HTTP/2, HTTP/3 and ALPN checker