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// http header · response header

ETag

Version identifier used for caching

What the ETag header does

An ETag is an opaque version identifier for a resource — change the resource, change the ETag. Clients send it back in If-None-Match to revalidate their cache, letting the server answer 304 Not Modified when nothing changed.

Example

ETag: "33a64df5"

Where it's used

ETag is a response header. Response headers are sent by the server to describe the response and tell the client how to handle it.

Other response headers

Content-Encoding Content-Disposition ETag Last-Modified Location Set-Cookie Server Retry-After WWW-Authenticate
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.