URL Encode and Decode

1. What is URL Encode and Decode?
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What is URL encoding?

URL encoding stands for encoding certain characters in a URL by replacing them with one or more character triplets that consist of the percent character "%" followed by two hexadecimal digits. The two hexadecimal digits of the triplet(s) represent the numeric value of the replaced character.

The term URL encoding is a bit inexact because the encoding procedure is not limited to URLs (Uniform Resource Locators), but can also be applied to any other URIs (Uniform Resource Identifiers) such as URNs (Uniform Resource Names). Therefore, the term percent-encoding should be preferred.

Which Characters Are Allowed in a URL?

The characters allowed in a URI are either reserved or unreserved (or a percent character as part of a percent-encoding). Reserved characters are those characters that sometimes have special meaning, while unreserved characters have no such meaning. Using percent-encoding, characters which otherwise would not be allowed are represented using allowed characters. The sets of reserved and unreserved characters and the circumstances under which certain reserved characters have special meaning have changed slightly with each revision of specifications that govern URIs and URI schemes.

According to RFC 3986, the characters in a URL have to be taken from a defined set of unreserved and reserved ASCII characters. Any other characters are not allowed in a URL.

The unreserved characters can be encoded, but should not be encoded. The unreserved characters are:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t u v w x y z
0 1 2 3 4 5 6 7 8 9 - _ . ~

The reserved characters have to be encoded only under certain circumstances. The reserved characters are:

! * ' ( ) ; : @ & = + $ , / ? % # [ ]