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MIME Type

Last modified 22:17, 27 Dec 2008

The MIME type identifies the type of representation contained in the body of a HTTP request or response using the Content-Type header.  MIME types were first used for email transmissions, as is evidenced by its full name: Multipurpose Internet Mail Extensions.  Sometimes MIME types are also referred to as MIME media types or Internet media types.

The MIME type has a type and subtype separated by a slash (e.g. text/plain, image/gif, ...) and followed by one or more optional parameters. The major types are application, audio, image, text, and video. Application refers to a variety of formats.  For example, application/pdf refers to Adobe Acrobat documents and application/octet-stream refers to an arbitrary binary stream.

A complete list of official MIME types can be found at IANA MIME type registry.

Character Sets

In addition to the major type and subtype, a MIME type may contain the specification for a character set.  If the character set is omitted, the character set is determined by the major type: Latin1 for text/* and UTF-8 for application/*.

Since HTML is defined as MIME type text/html it is often provided with an character set specification in Content-Type headers.

Content-Type: text/html; charset=utf-8

XML MIME Types

The most common XML MIME types are application/xml and text/xml. Note that the latter is discouraged, because it uses the Latin1 character set by default.  However, for XML MIME types, there is also a provision to allow for an infinite number of recognizable XML MIME types by using the +xml suffix (e.g. application/atom+xml, application/xhtml+xml, ...).

In general, XML MIME types are of the form application/*+xml with the notable exception of SVG, which is image/svg+xml.

Custom MIME Types

Custom MIME types can be created by following these conventions:

  • Use x. as prefix to the subtype for experimental MIME types.  Note that the x- prefix is also valid for this purpose, but is discourage in favor of x. to promote symmetry with other prefixes.
  • Use vnd. as prefix to the subtypte for vendor specific MIME types which are part of a commercial product.  The vnd. prefix should be followed by the vendor name and subtype separated by a period (e.g. application/vnd.mozilla.xul+xml).
  • Use prs. as prefix to the subtype for personal/vanity MIME types which aren't part of a commercial product.
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