html form submission type

When you make a POST request, you have to encode the data that forms the body of the request in some way.

HTML forms provide three methods of encoding.

  • application/x-www-form-urlencoded (the default)
  • multipart/form-data
  • text/plain

Work is being done on adding application/json.

The specifics of the formats don’t matter to most developers. The important points are:

When you are writing client-side code, all you need to know is use multipart/form-data when your form includes any <input type="file"> elements.

When you are writing server-side code: Use a prewritten form handling library (e.g. Perl’s CGI->param or the one exposed by PHP’s $_POST superglobal) and it will take care of the differences for you. Don’t bother trying to parse the raw input received by the server.

Never use text/plain.


If you are writing (or debugging) a library for parsing or generating the raw data, then you need to start worrying about the format. You might also want to know about it for interest’s sake.

application/x-www-form-urlencoded is more or less the same as a query string on the end of the URL.

multipart/form-data is significantly more complicated but it allows entire files to be included in the data. An example of the result can be found in the HTML 4 specification.

text/plain is introduced by HTML and is useful only for debugging — from the spec: They are not reliably interpretable by computer — and I’d argue that the others combined with tools (like the Net tab in the developer tools of most browsers) are better for that).

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