HTTPfy

306 (Unused)

Unused: reserved code, previously "Switch Proxy" in a draft; no longer used.

306 at a glance

Code
306
Name
(Unused)
Class
3xx Redirection
Status
Registered as reserved / unused
Defined in
RFC 9110, Section 15.4.7
Cacheable by default
No by default. Caches store it only when the response carries explicit freshness (Cache-Control max-age, s-maxage or Expires).

What 306 means

306 is reserved. It was used in a previous draft of HTTP/1.1 ("Switch Proxy") and dropped before publication; RFC 9110 keeps the number reserved so it is never reassigned. No compliant server sends it.

What typically causes a 306

  • None in practice. If you see it, the server is buggy or using it as a private code.

Fix it on the server

  • Pick a real redirect code (302, 307) instead.

Fix it as a client or visitor

  • Treat it as an unknown 3xx, i.e. like 300, per RFC 9110's rule for unrecognised codes.

Example response

HTTP/1.1 306 (Unused)

Opens the HTTP headers tool with your URL filled in; it shows the status line and headers of every redirect hop.

Checking a whole domain's redirects? The HTTP status checker follows http, https, www and non-www variants and shows every hop.