Happy Eyeballs
Webtester

Happy Eyeballs version 1 defines the racing of IPv4 vs. IPv6. The term Connection Attempt Delay (CAD) describes the delay a client waits for the IPv6 response before issuing an IPv4 connection. We test this behavior of your client by artificially adding latency to IPv6 packets. Depending on your client's settings, it will wait for the IPv6 connection attempt.

Happy Eyeballs version 2 defines the racing of A vs AAAA DNS queries and uses the term Resolution Delay (RD) to describe the configured accepted delay between A and AAAA responses. We test this behavior of your client by artificially adding latency to A or AAAA queries. In this test, not only your client but also the configured resolver and any forwarder in the resolution chain can impact the result.

Happy Eyeballs version 3 extends connection racing to the application layer, specifically racing QUIC against TLS/TCP. Browsers implementing this version should fall back to the alternative protocol if one is unresponsive to avoid blocking. We test this by varying the handshake delay to determine if and when your client decides to switch protocols.

Happy Eyeballs version 3 extends connection racing to the application layer. Browsers implementing this version should fall back between IP versions and protocols to avoid blocking if one is unresponsive. We test this by varying the handshake delay and IP version-specific delay to determine if and when your client decides to switch protocols and IP versions.

The test checks how your browser establishes connections when HTTP/3 is available. We simulate various scenarios where HTTP/3 can be discovered via Alt-Svc headers or HTTPS DNS records.