The Content-Encoding entity header is used to compress the media-type. When present, its value indicates which encodings were applied to the entity-body. It lets the client know how to decode in order to obtain the media-type referenced by the Content-Type header.

The recommendation is to compress data as much as possible and therefore to use this field, but some types of resources, such as jpeg images, are already compressed. Sometimes, using additional compression doesn't reduce payload size and can even make the payload longer.

Header type Entity header
Forbidden header name no

Syntax

Content-Encoding: gzip
Content-Encoding: compress
Content-Encoding: deflate
Content-Encoding: identity
Content-Encoding: br

// Multiple, in the order in which they were applied
Content-Encoding: gzip, identity
Content-Encoding: deflate, gzip

Directives

gzip
A format using the Lempel-Ziv coding (LZ77), with a 32-bit CRC. This is the original format of the UNIX gzip program. The HTTP/1.1 standard also recommends that the servers supporting this content-encoding should recognize x-gzip as an alias, for compatibility purposes.
compress
A format using the Lempel-Ziv-Welch (LZW) algorithm. The value name was taken from the UNIX compress program, which implemented this algorithm. Like the compress program, which has disappeared from most UNIX distributions, this content-encoding is not used by many browsers today, partly because of a patent issue (it expired in 2003).
deflate
Using the zlib structure (defined in RFC 1950) with the deflate compression algorithm (defined in RFC 1951).
identity
Indicates the identity function (i.e., no compression or modification). This token, except if explicitly specified, is always deemed acceptable.
br
A format using the Brotli algorithm.

Examples

Compressing with gzip

On the client side, you can advertise a list of compression schemes that will be sent along in an HTTP request. The Accept-Encoding header is used for negotiating content encoding.

Accept-Encoding: gzip, deflate

The server responds with the scheme used, indicated by the Content-Encoding response header.

Content-Encoding: gzip

Note that the server is not obligated to use any compression method. Compression highly depends on server settings and used server modules.

Specifications

Specification Title
RFC 7231, section 3.1.2.2: Content-Encoding Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content
RFC 7932: Brotli Compressed Data Format Brotli Compressed Data Format

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome 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
br
ExperimentalNon-standard
Chrome Full support 50Edge No support NoFirefox Full support 44IE No support NoOpera Full support 36Safari No support NoWebView Android Full support 51Chrome Android Full support 51Edge Mobile No support NoFirefox Android Full support 44Opera Android No support NoSafari iOS No support NoSamsung Internet Android Full support 5.0

Legend

Full support  
Full support
No support  
No 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.

See also

Document Tags and Contributors

Last updated by: jamesdhurd,