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// http header · request header

If-None-Match

Conditional request based on an ETag

What the If-None-Match header does

If-None-Match makes a request conditional on an ETag: the client sends the ETag it already has, and the server replies 304 Not Modified (no body) if the resource is unchanged. It's the core of efficient revalidation and saves bandwidth.

Example

If-None-Match: "33a64df5"

Where it's used

If-None-Match is a request header. Request headers are sent by the client to describe the request and what the client can accept.

Other request headers

Accept Accept-Encoding Accept-Language Authorization Content-Type Content-Length Cookie Host Origin Referer User-Agent If-None-Match Range
TOOL

HTTP Headers Parser

Turn a block of raw headers into readable JSON.

REFERENCE

All HTTP Headers

Common request, response, caching, CORS, and security headers.

GUIDE

How to Read and Parse HTTP Headers

The anatomy of headers and how to work with them.