1. Handling Special Symbols

Certain special symbols (like spaces and punctuation marks) cannot be used directly in a URL; otherwise, parsing errors will occur. Escape characters convert these symbols into a format of % + hexadecimal encoding values, making them valid within the URL.

• Examples:
  • A space ( ) should be escaped as %20 or + (the latter was an earlier convention, but %20 is now recommended).
  • The question mark (?), which separates the URL from query parameters, must be escaped as %3F if it needs to be passed as a regular character.
  • The percent sign (%), which is the escape character itself, must be escaped as %25 if it needs to be transmitted.

2. Supporting Non-ASCII Characters

URLs natively support only the ASCII character set (e.g., English letters, numbers). For non-ASCII characters like Chinese, Japanese, etc., escape characters are used to encode them into byte sequences of character sets such as UTF-8.

• Examples:
  • The Chinese characters “你好” have UTF-8 bytes E4 BD A0 E5 A5 BD, which are escaped as %E4%BD%A0%E5%A5%BD.
  • The Japanese character “あ” has UTF-8 bytes E3 81 82, which are escaped as %E3%81%82.

3. Ensuring Correct URL Semantics

Some symbols in URLs have special meanings (e.g., / represents path separation, # represents an anchor, & separates query parameters). If these symbols need to be passed as regular characters, they must be escaped to avoid misinterpretation.

• Examples:
  • The # in a path should be escaped as %23; otherwise, the browser will treat it as an anchor identifier.
  • The & in query parameters should be escaped as %26; otherwise, it will be mistaken for a parameter separator.

4. Compatibility with Different Systems and Protocols

Operating systems, browsers, or servers may handle URL characters differently. Escape characters serve as a unified encoding standard, ensuring that URLs can be correctly parsed across various environments.

• Use Cases:
  • Passing parameters with special symbols in HTTP requests (e.g., the @ in a password should be escaped as %40).
  • Embedding file paths, email addresses, or other content with special symbols in a URL.

Common URL Escape Characters Table

Original Character	Escaped Form	Description
Space	%20	One of the most common escape characters
?	%3F	Question mark
#	%23	Anchor symbol
%	%25	The percent sign itself
&	%26	Query parameter separator
=	%3D	Equal sign
+	%2B	Plus sign (formerly used for spaces)
"	%22	Double quote
,	%2C	Comma
<	%3C	Less than sign
>	%3E	Greater than sign
{	%7B	Left curly brace
}	%7D	Right curly brace
|	%7C	Separator
\	%5C	Backslash
^	%5E	Caret
~	%7E	Tilde
[	%5B	Left square bracket
]	%5D	Right square bracket
`	%60	Backquote
;	%3B	Semicolon
/	%2F	Slash
?	%3F	Question mark
:	%3A	Colon
@	%40	At symbol
$	%24	Dollar sign
Chinese “中”	%E4%B8%AD	UTF-8 encoded character “中”

Notes

1. Encoding Method:
   • Modern URLs typically use UTF-8 encoding for escaping to ensure multilingual support.
   • Avoid mixing different encodings (such as GBK), which may cause garbled text.
2. Automated Tools:
   • In programming, built-in functions can generate escaped URLs (e.g., encodeURIComponent() in JavaScript, urllib.parse.quote() in Python).
   • Manual escaping is error-prone; it’s recommended to use online URL encoding tools.

Through escape characters, URLs can safely and accurately transmit various complex characters, making them an essential foundation in network communication.