HTTP headers | If-None-Match

The HTTP Header If-None-Match is a request-type header. Generally, it is used to update the entity tags on the server. Firstly, the Client provides the Server with a set of entity tags (E-tags). The Server compares the given tags with those it already has for the resource. Then, the Server will provide the requested page with a 200 status code only when none of the entity tags given to it matches. Or else, a 304 Not Modified status is returned by the Server.

There are two types of algorithms used to compare the entity tags. They are:

  • Weak Comparison Algorithm
  • Strong Comparison Algorithm