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
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|
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
- 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-gzipas an alias, for compatibility purposes.
- 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).
- Using the zlib structure (defined in RFC 1950) with the deflate compression algorithm (defined in RFC 1951).
- Indicates the identity function (i.e., no compression or modification). This token, except if explicitly specified, is always deemed acceptable.
- A format using the Brotli algorithm.
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.
Note that the server is not obligated to use any compression method. Compression highly depends on server settings and used server modules.
|RFC 7932: Brotli Compressed Data Format||Brotli Compressed Data Format|
|RFC 7231, section 22.214.171.124: Content-Encoding||Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content|
|RFC 2616, section 14.11: Content-Encoding||Content-Encoding|
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The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.