MIME Type

application/x-www-form-urlencoded

Form

Traditional MIME type for HTML form submissions encoded as key-value pairs.

MIME type reference, HTTP example, browser usage, common mistakes, and related content.

What is the application/x-www-form-urlencoded MIME type?

The MIME type application/x-www-form-urlencoded is used to tell browsers, APIs, and servers how a file or response body should be interpreted.

MIME stands for Multipurpose Internet Mail Extensions, and MIME types are now a standard part of HTTP responses and web content delivery.

When a browser or client receives a response with application/x-www-form-urlencoded, it uses that information to decide how the content should be processed, rendered, downloaded, or executed.

Example

Content-Type: application/x-www-form-urlencoded

HTTP example

HTTP/1.1 200 OK
Content-Type: application/x-www-form-urlencoded
Content-Length: 1256

Common use cases

Classic form posts
Auth flows
Simple non-file form submissions

Common mistakes

Using the wrong MIME type for the file being served
Returning text/plain instead of application/x-www-form-urlencoded
Forgetting required parameters like charset when relevant
Using a deprecated MIME type in older server configurations
Serving assets with a mismatched Content-Type header, causing browser parsing issues

How browsers use it

Browsers use the Content-Type response header to decide how a response should be handled. For example, HTML is rendered as a page, CSS is parsed as styles, JavaScript is executed as script, and images are displayed visually. If the MIME type is incorrect, the browser may refuse to load the file correctly or may treat it as plain text or a download instead.

Developer note

Still common in login forms, payment flows, and older backend integrations.

Related MIME types

multipart/form-data text/plain application/json