Overview

application/x-www-form-urlencoded is the default encoding for submitting HTML forms via GET/POST, formatting fields as a `key=value&key2=value2` string identical to a URL query string. It reuses the percent-encoding used in query strings, placed in the body.

Details

Each name and value is percent-encoded, and spaces are replaced with `+` by historical convention (a decoder must turn `+` back into a space): e.g. `name=John+Doe&city=Seoul%2FKR`. The WHATWG URL standard's application/x-www-form-urlencoded parser defines these rules, and non-ASCII characters are percent-encoded as their UTF-8 bytes.

This type suits short textual key-value data but is a poor fit for file uploads: percent-encoding binary bloats the size, and there is no place for per-field metadata such as filenames or a per-part Content-Type. When files are involved, use multipart/form-data. For plain text forms, urlencoded is smaller and simpler to parse.

Syntax

e.g. Content-Type: application/x-www-form-urlencoded

Notes

• Values containing `&`, `=`, `+`, or `%` must be percent-encoded; skipping this breaks field boundaries and misaligns parsing.
• Servers impose limits on body size and field count (e.g. PHP's max_input_vars), so a large number of fields can be silently truncated.
• There is no charset parameter in the spec, so servers usually assume the form page's encoding (UTF-8). An old trick hints encoding via Accept-Charset or a hidden field.

Related types

Related headers