What did 306 Switch Proxy mean?
It appeared only in a draft of HTTP/1.1 and was meant to tell clients to switch proxies. It was never standardised, and the number is now permanently reserved.
HTTP 306 UNUSED (FORMERLY SWITCH PROXY)
Reserved. Was "Switch Proxy" in a draft and is no longer used. 306 belongs to the 3xx redirection class and is defined in RFC 9110.
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About HTTP 306
What Does HTTP 306 Unused (Formerly Switch Proxy) Mean?
Reserved. Was "Switch Proxy" in a draft and is no longer used. The code is registered with IANA and defined in RFC 9110.
Redirection: the client must take another step to finish the request. Every code from 300 to 399 shares that general meaning, so a client that does not recognise 306 must treat it like 300.
When Do You See a 306 Response?
306 is reserved and unused. A draft of HTTP/1.1 briefly defined it as Switch Proxy, to tell clients to use a different proxy for subsequent requests, but the idea was dropped before standardisation. IANA keeps the number reserved so nobody gives it a new meaning that old software could misread. No legitimate server sends 306, and if you see one it almost certainly comes from a bug or a test harness.
How Do You Handle a 306?
Never send 306. A client that receives it should apply the generic 3xx rule, treating it as an unspecified redirection, and should not follow it automatically. If one of your services returns 306, check for a hand-coded status number or a typo in a redirect helper. Pick a real redirect such as 302, 307, or 308 depending on whether the move is temporary and whether the method must be preserved.
What Does a 306 Response Look Like?
HTTP/1.1 306 (Unused)
(reserved: no server should send this status)306 is not cacheable by default: a browser or CDN stores it only when Cache-Control or Expires explicitly allows it.
To inspect a real one without sending it anywhere:
- Copy the response headers from your browser Network tab, or from
curl -i. - Paste them into the Header decoder to see every header explained.
- Check caching in the Cache lane and the Location target in the decoder.
Which Status Codes Are Related to 306?
- 305 Use Proxy: Deprecated. Clients ignore it for security reasons.
- 307 Temporary Redirect: A temporary redirect that keeps the method and body: a POST stays a POST.
- 302 Found: A temporary redirect. Clients may change POST to GET; use 307 to forbid that.
Browse every code on the HTTP status codes page.
What Other Lanes Are in the Reference Section?
- HTTP status codes: Every IANA-registered status code, with a page per code.
- MIME types: File extensions to Content-Type, searchable both ways, plus a Content-Type parser.
- HTTP methods: GET, POST, PUT, PATCH, DELETE and the rest: safe, idempotent, cacheable.
Elsewhere in 2http: Header decoder, Cookie decoder, Cache-Control decoder, CORS checker, User-agent parser, and all eleven lanes on the 2http home page. Part of the 2suite.io privacy-first ecosystem.
Frequently Asked Questions
Can I use 306 for my own purpose?
No. Reusing reserved codes confuses clients and proxies. Use a registered code that fits, or return a standard code with details in the body.
Is HTTP 306 an error?
No. 306 is reserved and unused, so a correct server never sends it; a client that receives it should treat it like a generic 3xx response.
Is a 306 response cacheable by default?
No. Caches store a 306 only when Cache-Control or Expires explicitly allows it.
How Can You Verify That Nothing Leaves This Browser?
You do not have to take our word that your headers stay here. Developer tools show every request a page makes, so you can watch this page work and confirm that nothing is sent. The check takes under a minute.
- Open your browser developer tools with
F12, orCmd+Option+Ion a Mac, and select the Network tab. - Reload the page and let it finish. You will see the page's own files, its web fonts, and one anonymous page-view request. Nothing has been typed yet, so none of them can contain your headers.
- Click the clear icon in the Network tab so that the log is empty.
- Paste real headers into any lane and read the result.
- Look at the Network tab again. It is still empty. For extra proof, turn on offline mode after the page loads and every lane keeps working.
Only two things can add a line to that log, and neither carries your headers. Submitting the feedback form sends the vote and comment you typed. Typing characters in a script the page has not displayed yet, such as Cyrillic or Greek, can make the browser fetch the matching font file, and that request names only the font.
2http never sends a request on your behalf: the request builder writes code for you to run, and the meta inspector reads source you paste instead of fetching a URL. The production site also sends a Content-Security-Policy header that tells your browser to refuse connections to anywhere except this site and the anonymous analytics endpoint.