What does HTTP status code 226 mean?
The 226 IM Used status code indicates that the server has fulfilled a GET request and the response is a representation of the result of one or more instance manipulations applied to the current instance, as negotiated using the A-IM request header.
When to use it in APIs
Defined by RFC 3229 for delta encoding, where a client that already holds an older version of a resource asks the server to return only the difference (the “delta”) rather than the full body. The server responds with 226 and an IM header identifying the instance manipulation (e.g., a diff algorithm) used to produce the payload, letting the client reconstruct the current version while saving bandwidth.
How it compares to other codes
- 200 OK: Returns the full current representation, whereas 226 returns only a delta relative to a version the client already has.
- 206 Partial Content: Returns a byte range of a resource requested via the
Rangeheader, while 226 returns a computed difference negotiated via theA-IMheader.
