Pragma Header

Table of Content

• Syntax
• Directives
• Examples
• Browser Compatibility
• How to modify Pragma header The Pragma header is a specific piece of HTTP 1.0 headers used to define the browser's cache policies. This header predominantly served as a directive for backward compatibility with HTTP/1.0 caches where the Cache-Control HTTP/1.1 header is not yet present. This header is only supposed to be implemented in client requests but bears no resemblance to the responses' cache-control. However, the pragmatic use of Pragma header has largely been superseded by Cache-Control Header.

Syntax

Pragma: no-cacheCopy

Directives

The only directive used with the Pragma header is no-cache. It was used for backwards compatibility with HTTP/1.0 as a way to preclude caching.

Examples

Below is an example of how to implement the Pragma header:

GET /index.html HTTP/1.1
Host: www.example.com
Pragma: no-cacheCopy

In this case, the client is requesting index.html but also instructing the server not to use a cached version of the page.

Browser Compatibility

How to modify Pragma header

ModHeader is a Chrome extension used for modifying HTTP requests headers. Using ModHeader to modify the Pragma header is as simple as adding a new header and setting its value.

1. Open the ModHeader extension.
2. Click on 'Add' under the 'Request headers' tab and a new row will appear.
3. Input 'Pragma' in the 'Name' section and 'no-cache' in the 'Value' section.

This way, for every new client request, the Pragma header will be set to 'no-cache', instructing servers not to use cached versions of pages, thereby retrieving the freshest content.