URL Encoder/Decoder

Why URL Encoding Matters

URL encoding, also known as percent-encoding, converts characters into a format safe for internet transmission. Since URLs only support ASCII, special characters like emojis, spaces, and non-Latin scripts must be encoded. UTF-8 encoding is the standard that converts any character into byte sequences, each byte represented as %HH. Without proper encoding, characters like & or = would break query parameter parsing and corrupt URL structure.

Reserved Characters Explained

Char	Name	Purpose
?	Question Mark	Separates path from query
&	Ampersand	Separates query parameters
=	Equals	Name-value separator
/	Slash	Path segment separator
#	Hash	Fragment identifier
%	Percent	Escape indicator

Characters That Need Encoding

Safe Characters

Only A-Z, a-z, 0-9, -, _, ., ~ are safe without encoding. All others require percent-encoding using UTF-8.

Common Use Cases

• Form Submission: Query parameters with special characters
• API Endpoints: URLs with dynamic path parameters
• Redirect URLs: Query strings and fragments
• HTML Links: Safe URL generation

Important Notes

URL encoding differs from Base64 encoding. URL encoding uses percent-encoding (%20 for space), while Base64 uses a different alphabet for binary data.

For query parameters, use encodeURIComponent() to properly encode all special characters including & and =.

Frequently Asked Questions

encodeURI vs encodeURIComponent?

Use encodeURI() when preserving /, ?, #. Use encodeURIComponent() for individual query values with any special characters.

Why %20 and not + for spaces?

Plus sign encoding is legacy form encoding. Modern URLs use %20 for spaces. Plus only appears in application/x-www-form-urlencoded form data.

How are Unicode characters encoded?

First converted to UTF-8 bytes, then each byte percent-encoded. 你好 becomes %E4%BD%A0%E5%A5%BD (3 bytes per character).

What happens without encoding?

Unencoded special characters break parsing, cause security vulnerabilities like parameter injection, or corrupt data transmission.

Can I decode multiple times?

Only if double-encoded. Typically decode once. Double encoding happens when data is encoded, then encoded again as part of another parameter.

Are hex digits case-sensitive?

Both %2F and %2f are valid and equivalent. Case-insensitive, though uppercase is conventionally used.