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3xx Redirection Reserved, unused

306 Unused (formerly Switch Proxy)

Reserved and unused. 306 was once proposed as "Switch Proxy" but dropped; it must not be used, and clients treat it as an unknown 3xx code.

Category
3xx Redirection
Reason phrase
(Unused)
Specification
RFC 9110, Section 15.4.7 (opens in a new tab)
Redirect
No
Cacheable by default
No

306 is reserved. In an Internet-Draft from the late 1990s it was proposed as Switch Proxy, meaning that the client should use the proxy given in a Set-Proxy header for its following requests. The idea was abandoned, and since RFC 2616 the code has been listed as unused. RFC 9110 keeps it reserved so that it is never given another meaning.

A client that receives 306 treats it like any unknown 3xx code, which means as 300 Multiple Choices: it is not followed automatically.

Example response

HTTP
HTTP/1.1 306 Switch Proxy
Date: Fri, 06 Nov 2026 10:15:32 GMT
Content-Length: 0

SEO and redirect checking

There is no legitimate use of 306. A URL that returns it will not be followed or indexed; use a standard redirect code instead.

Common causes and use cases

  • Custom or buggy server code sends 306 by mistake, usually meaning 307 or 302.
  • A test or demo endpoint deliberately returns unusual codes.
  • Replace any 306 with 307 or 308, depending on whether the move is temporary or permanent.

Related status codes

All HTTP status codes

URL Redirect Checker

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