Difference between the Accept and Content-Type HTTP headers

As you correctly note, the Accept header is used by HTTP clients to tell the server what content types they'll accept. The server will then send back a response, which will include a Content-Type header telling the client what the content type of the returned content actually is.

However, as you may have noticed, HTTP requests can also contain Content-Type headers. Why? Well, think about POST or PUT requests. With those request types, the client is actually sending a bunch of data to the server as part of the request, and the Content-Type header tells the server what the data actually is (and thus determines how the server will parse it).

In particular, for a POST request resulting from an HTML form submission, the Content-Type of the request will (normally) be one of the standard form content types below, as specified by the enctype attribute on the <form> tag:

• application/x-www-form-urlencoded (default, older, simpler, slightly less overhead for small amounts of simple ASCII text, no file upload support)
• multipart/form-data (newer, adds support for file uploads, more efficient for large amounts of binary data or non-ASCII text)

• Accept: is what the browser is able to digest, for example, all the languages someone can understand.
• Content-Type: is what format the actual data is in, for example what language someone is speaking. Since computers can't (well, now they can) recognize other types like people can say "oh, he's German!" or "she's speaking Chinese!"

Accept is like

Here is my request and I would like (to Accept) this response format

Content-Type is like

Here is my request (or response) and this (Content-Type) is the format of the content I am sending in my request (or response)