If-None-Match Header

Table of Content

  • Syntax
  • Directives
  • Examples
  • Browser Compatibility
  • How to modify If-None-Match header The If-None-Match HTTP request header makes the requested operation conditional. It is used to prevent redundant updates or to reduce unnecessary network traffic. The header field can contain one or more ETags. If any of the ETags match the current entity tags of the requested resource, the server must not perform the requested method, unless necessary to verify that the resource has not been modified.


If-None-Match: <etag_value>
If-None-Match: <etag_value>, <etag_value>, ...


<etag_value>: Entity tags uniquely representing the requested resources. They can be weak or strong and are enclosed in double quotes.


Example of a single ETag:

If-None-Match: "686897696a7c876b7e"

Example of multiple ETags:

If-None-Match: "686897696a7c876b7e", "abc123def456"

Browser Compatibility

Browser Compatibility
Chrome Supported
Firefox Supported
Safari Supported
Opera Supported
Edge Supported

How to modify If-None-Match header

ModHeader is a Chrome extension that can be used to modify the If-None-Match header. After installing and opening ModHeader, you can click 'Add' under 'Request headers'. In the 'Name' field, enter 'If-None-Match', and in the 'Value' field, enter your ETag. This can be useful for testing cache validations where you may want to simulate a specific ETag to ensure the server returns the desired response, such as a 304 Not Modified status, indicating that the client’s cached version is still up-to-date.