What is URL encoding?

URL Encoding (also known as percent-encoding) is a method to encode arbitrary data in a uniform resource identifier (URI) using only the ASCII characters legal within a URI.

URLs are designed to use characters from the ASCII character set. Because URLs often need to include characters outside this set (like spaces or non-ASCII characters), or characters with special meaning within the URL syntax, URL encoding is necessary.

How URL-Encoding works?

ASCII Characters:

For ASCII characters (code points 0–127), URL encoding checks if the character is "unreserved" (like letters, digits, -, _, ., ~). If it’s not, the character is replaced with a percent sign %followed by its two-digit hexadecimal ASCII value. For example, the space character ( ) has an ASCII value of 32, which is0x20in hex, so it becomes %20. Similarly,@ (ASCII 64) becomes %40.

Non-ASCII Characters:

For non-ASCII characters (code points above 127), the character is first encoded using UTF-8 into one or more bytes. Each byte is then percent-encoded separately. For instance, the Unicode character ✓ (U+2713) is UTF-8 encoded into three bytes: E2 9C 93, and these are percent-encoded as %E2%9C%93. This ensures characters from all languages and symbols can be safely represented in URLs using only ASCII-compatible sequences.

RFC 3986 defines "reserved characters" as those that have special meaning within the URL syntax. These characters must be encoded when they appear as data within a URL component, to prevent them from being misinterpreted as URL syntax.