226 IM Used

What HTTP 226 IM Used Means

The server fulfilled a GET request and the response is a result of instance manipulations applied to the current instance.

Part of HTTP Delta encoding: the response represents one or more transformations (deltas) applied to the resource rather than the full body.

Common Causes

• Client supports delta encoding (A-IM header)
• Server returns a delta instead of the full resource

How to Fix It (For Visitors)

• No action needed

How to Fix It (For Developers/Admins)

• Send the IM header listing the instance manipulations used
• Implement delta encoding only where it provides a benefit

Returning a 226 IM Used (Code Examples)

If you build APIs or web apps, here is how to send an HTTP 226 response and how to test for it:

Node.js (Express)

app.get('/resource', (req, res) => {
  res.status(226).json({ error: 'IM Used' });
});

Python (Flask)

@app.route('/resource')
def resource():
    return jsonify(error='IM Used'), 226

PHP

<?php
http_response_code(226);
header('Content-Type: application/json');
echo json_encode(['error' => 'IM Used']);

Check the status with curl

curl -I https://example.com/resource
# Look for: HTTP/1.1 226 IM Used

Frequently Asked Questions

What does HTTP 226 IM Used mean?

Part of HTTP Delta encoding: the response represents one or more transformations (deltas) applied to the resource rather than the full body. In short: The server fulfilled a GET request and the response is a result of instance manipulations applied to the current instance.

How should I handle an HTTP 226 IM Used response?

Send the IM header listing the instance manipulations used. Implement delta encoding only where it provides a benefit.

Official Specification

The 226 IM Used status code is defined in RFC 3229.

View the IANA HTTP Status Code Registry →