urlencoded

URLencoded refers to the method of encoding data within URLs by replacing certain characters with percent-encoded representations. It is widely used to transmit non-ASCII data and reserved characters in query strings and form data. The encoding method, percent-encoding, converts a byte value to a percent sign followed by two hexadecimal digits. In URIs, unreserved characters (A–Z, a–z, 0–9, and "-", ".", "_", "~") may appear unencoded; all other characters should be percent-encoded. For spaces, application/x-www-form-urlencoded encoding commonly represents them as plus signs (+) in query components of forms, though percent-encoded space (%20) is also valid. In path components, spaces are typically encoded as %20.

In web forms, data submitted via HTTP POST with content type application/x-www-form-urlencoded is encoded with key=value pairs joined by ampersands, with reserved characters percent-encoded and spaces often as pluses. For query strings in URLs, the same encoding is used, and libraries vary whether they produce + or %20 for spaces.

JavaScript provides encodeURIComponent and encodeURI functions to perform URL encoding; the former encodes most non-URI characters, while the latter preserves URI-reserved characters. In server and client code, libraries implement percent-encoding with UTF-8 by default, turning non-ASCII characters into a sequence of bytes before percent-encoding each byte.

Limitations include that URL encoding is not a secure form of encryption; characters in untrusted input should be validated and sanitized. It is defined by standards such as RFC 3986 (percent-encoding, URI syntax).