226

IM Used

2xx Success

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Server perspective

Use 226 when the response body is not the full current representation, but the result of an agreed instance manipulation such as delta encoding.

When to use

  • •Return 226 only when the client explicitly negotiated a supported instance manipulation
  • •Use it for specialized caching or synchronization flows, not mainstream JSON APIs

How to respond

  • •Document the manipulation algorithm and negotiation rules clearly
  • •Make sure validators and reconstruction rules let the client rebuild the intended current representation

Headers to consider

  • •A-IM
  • •If-None-Match
  • •IM
  • •Delta-Base
  • •ETag

Response body

  • •Return the manipulated or delta-encoded payload, not the plain full representation

Server-side pitfalls

  • •Do not use 226 when the client does not understand the negotiated manipulation
  • •Do not confuse 226 with byte ranges or application-level patch documents

Examples

Delta sync response

Request:GET /feed with A-IM: diffe
Response:226 IM Used with delta instructions and validators

The server optimizes transfer by sending a reconstruction delta instead of the full resource.

References

Related 2xx Success Codes

200

OK

Everything worked perfectly! The server understood your request and sent back exactly what you asked for.

201

Created

Something new was created! Like adding a new post, user account, or file - the server made it and it now exists.

202

Accepted

We got your request and we're working on it! We'll process it later, but don't wait around - check back later to see if it's done.

203

Non-Authoritative Information

The request worked, but the response may have been adjusted by something in the middle, like a proxy, before it reached you.

204

No Content

Success. The server did what you asked, but there’s nothing useful to send back in the body.

205

Reset Content

Success! We did what you asked, and now please clear your form or reset your page so you can start fresh.

206

Partial Content

You asked for just a piece of a file (like pages 5-10 of a book), and here's that specific piece you wanted!

207

Multi-Status

I did multiple things for you - some worked, some didn't. Here's a detailed report of what happened to each item.

WebDAV
208

Already Reported

The server is saying, 'I already told you about this item earlier in the same detailed report, so I’m not repeating it.'

WebDAV