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HTTP Header
If-None-Match
CachingMakes the request conditional based on an ETag value.
HTTP header reference, syntax, examples, and developer usage.
What is the If-None-Match header?
The If-None-Match 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
If-None-Match: "etag-value"
Example
If-None-Match: "abc123"
Common use cases
- Cache validation
- Preventing unnecessary downloads
- Conditional GET requests
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