ErrorFindly
2262xx SuccessNone

HTTP 226 IM Used

Defined in RFC 3229

What Does HTTP 226 Mean?

The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.

Common Causes

  1. 1Delta encoding response for bandwidth optimization
  2. 2Server applying instance manipulations to cached content
  3. 3Differential content delivery for efficiency

Impact

  • ⚠Content loads with reduced bandwidth usage
  • ⚠No visible difference to the user

Developer Fix

For web developers and application engineers

  1. 1Implement delta decoding in client if using IM
  2. 2Handle IM header negotiations properly
  3. 3Fall back to full content if delta fails

Server Admin Fix

For system administrators and DevOps engineers

  1. 1Configure instance manipulation support if needed
  2. 2Monitor bandwidth savings from delta encoding
  3. 3Ensure proper A-IM header handling

Frequently Asked Questions

Is 226 IM Used commonly encountered?
No, it is extremely rare in practice. Most servers use standard caching (304 Not Modified) or compression (gzip/brotli) instead of instance manipulations.
What is delta encoding in HTTP?
Delta encoding sends only the differences between the client's cached version and the current version, reducing bandwidth. The 226 status indicates this optimization was applied.

Related HTTP Status Codes

200OK304Not Modified

About the Author

Web Infrastructure Team

Verified against official RFC specifications and real-world server configurations. HTTP status code behavior confirmed across Apache, Nginx, and Cloudflare.