The If-Match HTTP request header makes the request conditional. For GET and HEAD methods, the server will send back the requested resource only if it matches one of the listed ETags. For PUT and other non-safe methods, it will only upload the resource in this case.

The comparison with the stored ETag uses the strong comparison algorithm, meaning two files are considered identical byte to byte only. This is weakened when the  W/ prefix is used in front of the ETag.

There are two common use cases:

  • For GET and HEAD methods, used in combination with an Range header, it can guarantee that the new ranges requested comes from the same resource than the previous one. If it doesn't match, then a 416 (Range Not Satisfiable) response is returned.
  • For other methods, and in particular for PUT, If-Match can be used to prevent the lost update problem. It can check if the modification of a resource that the user wants to upload will not override another change that has been done since the original resource was fetched. If the request cannot be fulfilled, the 412 (Precondition Failed) response is returned.
Header type Request header
Forbidden header name no

Syntax

If-Match: <etag_value>
If-Match: <etag_value>, <etag_value>, …

Directives

<etag_value>
Entity tags uniquely representing the requested resources. They are a string of ASCII characters placed between double quotes (Like "675af34563dc-tr34") and may be prefixed by W/ to indicate that the weak comparison algorithm should be used.
*
The asterisk is a special value representing any resource.

Examples

If-Match: "bfc13a64729c4290ef5b2c2730249c88ca92d82d"

If-Match: W/"67ab43", "54ed21", "7892dd"

If-Match: *

Specifications

Specification Title
RFC 7232, section 3.1: If-Match Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic support
ExperimentalDeprecatedNon-standard
Chrome Full support YesEdge Full support YesFirefox Full support YesIE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support YesOpera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yes

Legend

Full support  
Full support
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.
Deprecated. Not for use in new websites.
Deprecated. Not for use in new websites.

See also

Document Tags and Contributors

Contributors to this page: mfuji09, ExE-Boss, fscholz, teoli
Last updated by: mfuji09,