URLs (Uniform Resource Locators) can only contain a very limited set of characters from the US-ASCII charset. These characters include upper and lowercase alphabets (
A-Za-z), digits (
0-9), and the special characters (
Some ASCII characters like
/ have special meaning within URLs. Other ASCII characters like
newline are unprintable. All these ASCII characters and any non-ASCII character must be encoded so that it can be safely placed inside URLs
Following class of characters are not allowed within URLs:
- Reserved characters: Some characters like
=are reserved for special purpose in the URLs. For example, the character
?is used to specify query parameters, the character
&is used to separate two query parameters. These characters cannot be placed in URLs without encoding.
- Unprintable characters: ASCII characters in the range 0-31 and 127 are unprintable. These are also called control characters. These characters are not allowed in URLs.
- Unsafe characters: Other ASCII characters like
\are considered unsafe and are not allowed in URLs.
- Non-ASCII characters: Any character outside the US-ASCII charset are not allowed in URLs.
%20 is the percent encoding of the
%2f is the percent encoding of forward slash (
%3f is the percent encoding of question mark (