URL encoding is the practice of translating unprintable characters or characters with special meaning within URLs to a representation that is unambiguous and universally accepted by web browsers and servers. These characters include:

• ASCII control characters – Unprintable characters typically used for output control. Character ranges 00-1F hex (0-31 decimal) and 7F (127 decimal). A complete encoding table is given below.
• Non-ASCII control characters – These are characters beyond the ASCII character set of 128 characters. This range is part of the ISO-Latin character set and ncludes the entire “top half” of the ISO-Latin set 80-FF hex (128-255 decimal). A complete encoding table is given below.
• Reserved characters – These are special characters such as the dollar sign, ampersand, plus, common, forward slash, colon, semi-colon, equals sign, question mark, and “at” symbol. All of these can have different meanings inside a URL so need to be encoded. A complete encoding table is given below.
• Unsafe characters – These are space, quotation marks, less than symbol, greater than symbol, pound character, percent character, Left Curly Brace, Right Curly Brace , Pipe, Backslash, Caret, Tilde, Left Square Bracket , Right Square Bracket, Grave Accent. These character present the possibility of being misunderstood within URLs for various reasons. These characters should also always be encoded. A complete encoding table is given below.

The encoding notation replaces the desired character with three characters: a percent sign and two hexadecimal digits whose correspond to the position of the character in the ASCII character set.

Example:

One of the most common special characters is the space. You can’t type a space in a URL directly. A space position in the character set is 20 hexadecimal. So you can use %20 in place a space when passing your request to the server.

http://www.example.com/new%20pricing.html

This URL actually retrieves a document named new pricing.html from the www.example.com

ASCII control characters encoding

This includes the encoding for character ranges 00-1F hex (0-31 decimal) and 7F (127 decimal)

Non-ASCII control characters encoding

This includes the encoding for the entire “top half” of the ISO-Latin set 80-FF hex (128-255 decimal.)

Reserved characters encoding

Following is the table to be used to encode reserved characters.

Unsafe characters encoding

Following is the table to be used to encode unsafe characters.

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