Character Encoding Chart
To help promote the cause of Web Standards and adhering to specifications, here is a quick reference chart explaining which characters are “safe” and which characters should be encoded in URLs.
Classification Included characters Encoding required?
Safe characters Alphanumerics [0-9a-zA-Z], special characters $-_.+!*'(), and reserved characters used for their reserved purposes (e.g., question mark used to denote a query string) NO
ASCII Control characters Includes the ISO-8859-1 (ISO-Latin) character ranges 00-1F hex (0-31 decimal) and 7F (127 decimal.) YES
Non-ASCII characters Includes the entire “top half” of the ISO-Latin set 80-FF hex (128-255 decimal.) YES
Reserved characters $ & + , / : ; = ? @ (not including blank space) YES*
Unsafe characters Includes the blank/empty space and " < > # % { } | \ ^ ~ [ ] ` YES
* Note: Reserved characters only need encoding when not used for their defined, reserved purposes.
Usafe Characters
More about “unsafe” characters from RFC1738:
Characters can be unsafe for a number of reasons. The space character is unsafe because significant spaces may disappear and insignificant spaces may be introduced when URLs are transcribed or typeset or subjected to the treatment of word-processing programs. The characters “<” and “>” are unsafe because they are used as the delimiters around URLs in free text; the quote mark (“"”) is used to delimit URLs in some systems. The character “#” is unsafe and should always be encoded because it is used in World Wide Web and in other systems to delimit a URL from a fragment/anchor identifier that might follow it. The character “%” is unsafe because it is used for encodings of other characters. Other characters are unsafe because gateways and other transport agents are known to sometimes modify such characters. These characters are “{”, “}”, “|”, “\”, “^”, “~”, “[”, “]”, and “`”.
All unsafe characters must always be encoded within a URL. For example, the character “#” must be encoded within URLs even in systems that do not normally deal with fragment or anchor identifiers, so that if the URL is copied into another system that does use them, it will not be necessary to change the URL encoding.
