URL encoding or URL escaping is a way of representing special characters and non-ASCII characters in a URL, using percent-encoding or percent-notation. This is necessary because some characters have special meanings in URLs, and certain browsers or servers may not handle these characters correctly if they are not encoded. The percent-encoding was introduced as a way to safely transmit special characters in URLs as part of the HTTP/1.0 specification in 1996.
When a character is encoded using percent-encoding, it is replaced by a sequence of three characters: a percent sign ("%") followed by two hexadecimal digits that represent the ASCII code for the original character. For example, the percent-encoded string "%20" represents a space character.
A URL-decoder calculator can decode such strings, replacing the encoded sequences with their corresponding ASCII characters. In addition to reserved characters such as space, the calculator can decode UTF-8 encoded characters, which are represented by a sequence of percent-encoded bytes.