MimeType

A MIME type, or media type, is a label that identifies the format and nature of a piece of data. It is typically written as type/subtype, with optional parameters. The term mimetype is commonly used as shorthand in programming contexts. MIME types are standardized and registered to help software understand how to process content, particularly in networking and email.

The type component is a broad category such as application, audio, image, text, video, multipart, font, or message. The subtype specifies a specific format, for example html, json, jpeg, or mp4. Parameters can follow after a semicolon, with charset being a common parameter for text types, as in text/html; charset=UTF-8. These parameters may convey character encoding, boundaries for multipart messages, or other processing hints.

MIME types are used in various protocols. In HTTP, the Content-Type header tells clients how to interpret the body of a response. In emails, MIME parts carry type information so recipients and mail agents can handle attachments correctly. Applications use MIME types to select decoders, renderers, or editors.

Registration and maintenance of MIME types are handled by the IANA MIME Media Types registry. New types are defined by IANA in coordination with standards bodies, vendors, and communities. Some legacy or experimental types may be defined with caveats, and some old extensions do not map reliably to a single MIME type.

While MIME types aim to be precise, there is no universal mapping from file extensions to types. Content sniffing and misreporting can cause security risks, so systems should rely on explicit Content-Type values and validate inputs accordingly.

Common examples include text/plain, text/html, application/json, image/jpeg, audio/mpeg, and video/mp4.