HTTP 226 — IM Used
HTTP 226 is the delta-encoding response: the server applied instance manipulations the client requested via the A-IM header and returns the resulting delta rather than a full representation.
When 226 shows up
- Bandwidth-conscious clients fetching only changed parts of a resource.
- Proxy layers that negotiate delta encodings to save transfer.
Mocking a 226 response
A response with this status can be faked end to end with a local mock rule — no backend changes needed. The configuration below mirrors the rule fields the ApiSimul editor uses (method, path, status, delay in milliseconds, response body):
{
"method": "GET",
"path": "/api/feed",
"status": 226,
"delay": 240,
"enabled": true,
"body": null
}Dynamic placeholders such as {{random.name}}, {{string.uuid}} or {{number.int 1 100}} can appear inside the body to vary each response, which keeps client-side list rendering and retry logic honest during development.
Frequently asked questions
What does HTTP 226 mean?
The response is the result of applying the requested instance manipulations — a delta applied on top of a cached base, not a fresh full copy.
How can I test a 226 response without a real backend?
Define a mock rule with the method and path your client requests and set the status to 226. The example configuration above returns this response after the listed delay, so the client exercises its 226 handling exactly as it would against a live server.
Related status codes
Need the response in your own project? Spin up rules for any status with the ApiSimul mock server, or browse every status code page.