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HTTP Header
ETag
CachingProvides a unique identifier for a specific version of a resource.
HTTP header reference, syntax, examples, and developer usage.
What is the ETag header?
The ETag HTTP header is used to transmit metadata between a client and server as part of HTTP requests or responses.
HTTP headers define how content should be interpreted, cached, authenticated, secured, or processed by browsers and APIs.
Direction
This header may appear in both HTTP requests and responses.
Syntax
ETag: "identifier"
Example
ETag: "abc123"
Common use cases
- Conditional requests
- Browser cache validation
- Reducing unnecessary downloads
Common mistakes
- Using the header in the wrong request or response context
- Sending invalid header values
- Incorrect header syntax
- Assuming the header automatically changes server behaviour