Will iPhones on iOS 26 or new Chrome versions fail to connect to my server?
Enter your domain. We send each host the large ClientHello that current browsers send, and flag hosts that drop it.
What this checks
- Whether each host accepts a ClientHello large enough to carry X25519MLKEM768.
- Hosts that answer a small ClientHello but drop the large one.
What it can't see
- Middleboxes on your users' own networks.
- Hosts behind a CDN are tested at the CDN's edge.
Questions
Why would a larger ClientHello fail?
Some firewalls, load balancers and old TLS stacks assume the first message fits in one packet. A post-quantum key share makes it larger, and they drop the connection.
How do I fix it?
Update the device or software that drops it (often a load balancer or firewall). Until then, browsers that offer post-quantum key exchange may fail to connect.