SVCB / HTTPS
An HTTPS record gives a browser connection information about a server before it even opens a connection to it: which application-layer protocols it supports, which port, and a handful of other details that would otherwise only be discovered after connecting. SVCB is the general-purpose record type behind it; HTTPS is specifically SVCB pre-configured for web traffic, the only variant most people will ever see in practice.
| Name | Type | Value |
|---|---|---|
| (apex) | HTTPS | 1 . alpn=h2,h3 |
Reading that value
The 1 is a priority, the same lower-goes-first idea as MX and SRV, letting more than one record offer alternatives. The single dot means "this same name", rather than pointing traffic somewhere else the way a CNAME would. What follows are params: alpn=h2,h3 advertises which application-layer protocols this server supports, HTTP/2 and HTTP/3 here, information a browser would otherwise only learn by actually negotiating it during the connection itself. Other params can hint at a specific port, or carry an IP address directly (ipv4hint / ipv6hint) so a browser doesn't need a separate A or AAAA lookup at all.
What this actually saves
The point of the record is handing a browser connection information up front, rather than making it discover the same details only after connecting. That reduces how much needs figuring out through the connection itself, fewer lookups, fewer round trips, but it's a reduction rather than a guarantee of zero: a browser can still need a follow-up query in some situations even with this record in place. None of it is required for a site to work either way, a browser falls back to its usual behaviour without it.
Encrypted Client Hello, mentioned rather than explained
One param worth knowing exists without needing to master it here: ech=, which carries the configuration for Encrypted Client Hello, a mechanism that hides which specific site is being requested from anyone observing the connection's very first exchange, even though the connection is already using HTTPS. Setting it up depends heavily on the hosting platform in use, which is why it's flagged rather than walked through on this page.
Building one
Expert Tools' SVCB / HTTPS check reads an existing record's params back in plain language, including the ones this page only mentions in passing, and its own wizard assembles one for you to review and publish.