URL Encoding Guide: What is URL Encoding & How to Encode/Decode URLs

Table of Contents

What is URL Encoding?
Reserved vs Unreserved Characters
How URL Encoding Works
When Do You Need URL Encoding?
URL Encoding in Code

What is URL Encoding?

URL encoding (also called percent encoding) converts characters that are not allowed in URLs into a format that can be safely transmitted. Each disallowed character is replaced with a percent sign (%) followed by two hexadecimal digits representing the character's ASCII or UTF-8 value.

For example, a space character becomes %20, the @ symbol becomes %40, and the & symbol becomes %26.

💡 Why it matters

Without URL encoding, a search query containing & would be interpreted as a URL parameter separator, completely breaking the request.

Reserved vs Unreserved Characters

URL characters fall into two categories:

Unreserved characters — safe to use in URLs without encoding: letters A–Z a–z, digits 0–9, and the symbols - _ . ~

Reserved characters — have special meaning in URLs and must be percent-encoded when used as data (not as delimiters):

Character	Encoded form	URL meaning
Space	%20 (or +)	Not allowed
&	%26	Parameter separator
=	%3D	Key-value separator
?	%3F	Query string start
#	%23	Fragment identifier
+	%2B	Sometimes used for space
/	%2F	Path separator
@	%40	Userinfo separator

How URL Encoding Works

The encoding process converts each character to its UTF-8 byte sequence, then represents each byte as %XX where XX is the hexadecimal value.

Example: encoding the text "hello world & more"

Space → %20
& → %26
Result: hello%20world%20%26%20more

For non-ASCII characters like accented letters or emoji, each byte of the UTF-8 encoding is encoded separately. The emoji 🎉 (U+1F389) becomes %F0%9F%8E%89.

When Do You Need URL Encoding?

Search queries — user input passed as a URL parameter must be encoded to prevent breaking the query string.
API requests — parameters containing special characters must be encoded before being appended to API URLs.
Form submissions — browsers automatically encode form data, but manual API calls require encoding.
Redirect URLs — a redirect target URL passed as a parameter must itself be encoded.
File names in URLs — file names containing spaces or special characters must be encoded.

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URL Encoding in Code

Every major language includes built-in URL encoding functions:

JavaScript: encodeURIComponent("hello world") — encodes a single component. Use encodeURI() for full URLs.

Python: from urllib.parse import quote; quote("hello world")

PHP: urlencode("hello world")

⚠️ Common mistake

In JavaScript, use encodeURIComponent() for individual query parameter values, not encodeURI(). The latter does not encode &, =, and ? which are reserved in query strings.

Frequently Asked Questions

Both represent a space, but in different contexts. %20 is the standard percent-encoding and works everywhere. The + sign represents a space only in application/x-www-form-urlencoded data (HTML form submissions). Use %20 in URL paths; + is only valid in query strings of form-encoded data.

No. You should only encode the values within a URL — not the protocol, domain, path separators, or query string delimiters. Use encodeURIComponent() for individual values and encodeURI() for a complete URL that may already contain structural characters.

URL encoding replaces special characters with %XX sequences to make them safe for URLs. Base64 converts binary data into a text string using 64 printable characters. They solve different problems — URL encoding is for making data safe in URL context; Base64 is for encoding binary data as text.

The + convention for spaces comes from the HTML form encoding standard (application/x-www-form-urlencoded). Browsers use + when submitting form data. Modern practice prefers %20 as it is unambiguous in all URL contexts.

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