URL Encoding Explained: When and Why to Encode URLs

What Is URL Encoding?

URL encoding (also called percent💡 Definition:A fraction or ratio expressed as a number out of 100, denoted by the % symbol.-encoding) converts characters into a format safe for URLs. Since URLs can only contain a limited set of ASCII characters, special characters must be encoded as %XX where XX is the hexadecimal value.

For example:

• Space → %20 or +
• Ampersand → %26
• Question mark → %3F
• Equals sign → %3D

Why URL Encoding Exists

URLs have special characters with specific meanings:

• ? separates the path from query parameters
• & separates query parameters
• = separates parameter names from values
• / separates path segments
• # indicates a fragment

If your data contains these characters, they must be encoded to avoid being misinterpreted.

Characters That Must Be Encoded

Always Encode

• Space: %20 (or + in query strings)
• Ampersand: %26
• Plus sign: %2B
• Percent: %25
• Question mark: %3F
• Hash: %23
• Non-ASCII characters: UTF-8 bytes as %XX

Safe Without Encoding

• Letters: A-Z, a-z
• Numbers: 0-9
• Unreserved: - _ . ~

Reserved (Context-Dependent)

• : / ? # [ ] @ ! $ & ( ) * + , ; =

Common Mistakes

1. Double Encoding

2. Not Encoding User Input

3. Using encodeURI vs encodeURIComponent

When to Encode vs Decode

Encode When:

• Building URLs with dynamic content
• Passing user input in query strings
• Including special characters in URL parameters
• Creating data URIs

Decode When:

• Reading query parameters from a URL
• Displaying URLs to users
• Processing form submissions
• Parsing URL-encoded data

URL Encoding in Different Languages

JavaScript

Python

PHP

Note: PHP urlencode uses + for spaces (form encoding), while rawurlencode uses %20 (standard URL encoding).

Space: + vs %20

There are two valid ways to encode spaces:

• %20: Standard URL encoding (RFC 3986)
• +: Form encoding (application/x-www-form-urlencoded)

Both are valid in query strings, but + is specific to form data. When in doubt, use %20 as its more universally supported.

International Characters

Non-ASCII characters (like ü, 中, or 🎉) are encoded as their UTF-8 bytes:

• ü (U+00FC) → %C3%BC
• 中 (U+4E2D) → %E4%B8%AD
• 🎉 (U+1F389) → %F0%9F%8E%89

This ensures URLs work correctly regardless of character encoding.

Testing Your URLs

Use our URL Encoder to test encoding and decoding. Common issues to check:

• Are all special characters properly encoded?
• Is the URL not double-encoded?
• Do international characters display correctly after decoding?