There are two parties that could be responsible for determining whattype of content you are getting in a HTTP response, whether the data isHTML or a PDF or a JPEG or so on: the server or the client. The web hasopted to make it determined by the server ,and this is the correct place for a simple reason: consistency .

Imagine a world where the clients determine what the content type is.If there is no standard for how clients determine the content type, theconsistency problems are obvious;

When a web server answers your request for a URL, you get boththe contents of the URL and its type; ie, whether you are gettingHTML, plain text, a PNG image, a PDF, and so on. Specifically, thistype information is returned in the form of a MIME type in the Content-Type: HTTP reply header.

(Some web browsers then sniff the data themselves and second guess theweb server, generally with ruinous results.)

Now, the web server has to get this