What is the HTTP Content-Type Header?

About

The Content-Type is a http header that defines the data type of the body of:

a request
or a response.

It specifies:

the mime type (mandatory)
and optionally the parameters of the mime:
- such as the character

The requested mime type of a request is specified by the accept header

Example

Resources	MIME type
HTML	text/html
JSON	text/json
XML	text/xml

See the MIME page for more.

Management

Set

See header set on how to set an header.

Example with an html meta

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>

Sniffing

When the Content-Type is not specified, a user agent such as browser may obtain it through sniffing.

Many web servers supply incorrect Content-Type header fields with their HTTP responses. In order to be compatible with these servers, user agents consider the content of HTTP responses as well as the content-Type header fields when determining the effective media type of the response.

Configuration to prevent sniffing with the X-Content-Type-Options header

X-Content-Type-Options: nosniff

The specification document describes an algorithm for determining the effective media type of HTTP responses that balances security and compatibility considerations.