field Registered
Verified 2026-09-18 · registry updated
2026-08-28Alt-Used
Indicates the alternative service used to reach an origin.
Use Alt-Used with Alt-Svc diagnostics; it does not redirect the origin or replace certificate and authority validation.
httpheaderhttp2http3
Reference (http)
Alt-Used: example.com
Use Alt-Used with Alt-Svc diagnostics; it does not redirect the origin or replace certificate and authority validation.
Common mistakes
- Treating Alt-Used as proof that an alternative endpoint is trusted.
IANA registry: http-fields/field-names
Registry reference: RFC 7838: HTTP Alternative Services