Happy Eyeballs
Testing: SVCB/HTTPS Early Hints Test

Under Development: This test is currently a work in progress.

This test verifies whether clients utilize ipv4hint and ipv6hint from SVCB/HTTPS records to start connection attempts before the explicit A and AAAA records are received (Section 4.2.1).

Our DNS server intentionally delays its responses to A and AAAA queries but returns the HTTPS record immediately. Clients that use the hints embedded in the HTTPS record can begin the TCP or QUIC handshake right away; clients that wait for the A/AAAA responses will be blocked for the full delay duration.

The test runs two rows: With ipv4hint/ipv6hint uses an HTTPS record that includes address hints; Without hints (control) uses an HTTPS record without hints — a client that ignores hints should behave identically to the control row. Click or hover on any result badge to inspect the total fetch duration and DNS lookup duration: if hints are effective, the total time in the hint row stays short across all delay values while the control row grows proportionally with the delay.

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