Last-Modified Header

Table of Content

  • Syntax
  • Directives
  • Examples
  • Browser Compatibility
  • How to modify Last-Modified header The Last-Modified response HTTP header provides the date and time when the origin server believes the resource was last modified before the request was made. This is used with cache validation to allow browsers to check if a cached copy of the page is up-to-date, valid and does not need to be re-fetched. This makes load times faster and reduces server load.


The Last-Modified HTTP header uses the following syntax:

Last-Modified: day_name, day month year hrs:min:sec GMT


The Last-Modified header only contains the date directive, which determines the last time the document was modified.


For a file that was modified on 25th October 2021 at 15:30:00 GMT, the Last-Modified header would look like:

Last-Modified: Mon, 25 Oct 2021 15:30:00 GMT

Browser Compatibility

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

How to modify Last-Modified header

ModHeader is a browser extension that allows you to modify HTTP request and response headers. To change the Last-Modified header with ModHeader in Chrome, perform the following steps:

  1. Click the ModHeader icon at the top right of Chrome to open its panel.
  2. In the Response headers section, click Add.
  3. In the Header name field, enter Last-Modified.
  4. In the Header value field, enter the time you want, such as Wed, 21 Oct 2018 07:28:00 GMT.
  5. Click Add to apply your changes.

The extension inserts the header before the server responds, which is useful for testing how your app behaves when receiving different Last-Modified values. Please be wary of using it on production environments, as it can affect the cache behavior.