HTTP 226 — IM Used
HTTP 226
IM Used
The server is returning a delta against a copy the client already has, rather than the whole resource.
What 226 actually means
From the "delta encoding in HTTP" extension: rather than resending an entire document that changed slightly, the server sends only the difference, and answers 226 to say the body is one or more instance manipulations applied to the client's cached copy. It was a clever idea that almost nothing implements. If you have met it at all, it was probably in an academic paper or a protocol test suite.
Common causes
- A client sent `A-IM:` requesting delta encoding and the server supports it
- A specialised sync or replication system built on RFC 3229
If you're just trying to view the page
- Nothing — effectively never seen in normal browsing
- If a tool reports one, the request succeeded; the body is a patch rather than the whole document
If it's your site
- Do not build on this; support is essentially nonexistent in browsers and CDNs
- For efficient updates, use conditional requests with ETags, or a purpose-built sync protocol
Reference
- Status code
- 226
- Reason phrase
- IM Used
- Category
- 2xx — Success
- Defined in
- RFC 3229 §10.4.1
Common questions
- What does HTTP 226 mean?
- The server is returning a delta against a copy the client already has, rather than the whole resource. From the "delta encoding in HTTP" extension: rather than resending an entire document that changed slightly, the server sends only the difference, and answers 226 to say the body is one or more instance manipulations applied to the client's cached copy. It was a clever idea that almost nothing implements.
- How do I fix a 226 error?
- Nothing — effectively never seen in normal browsing
- Is 226 a client error or a server error?
- 226 is in the 2xx range, which means success. It is not an error at all.
Related pages
- 200 OK The request worked and the response contains what was asked for.
- 204 No Content The request succeeded and there is deliberately no body to send back.
- 201 Created The request succeeded and a new resource was created as a result.
- 206 Partial Content The server is returning only the requested byte range of a file, not the whole t
- 202 Accepted The request was accepted for processing, but the work has not finished yet.
- 207 Multi-Status A WebDAV response carrying separate status codes for several resources at once.
- 203 Non-Authoritative Information The request succeeded, but an intermediary modified the response on the way.
- 205 Reset Content The request succeeded and the client should clear the form that sent it.
- 208 Already Reported Inside a WebDAV multi-status response, this member was already listed earlier so