URL Encode/Decode

What is URL Encoding?

URL encoding, also known as Percent-encoding, is a mechanism for encoding information in a Uniform Resource Identifier (URI). Since URLs can only be sent over the Internet using the ASCII character-set, any characters outside this set must be converted into a valid ASCII format.

Reserved vs. Unreserved Characters

Characters in a URL are divided into two categories:

• Unreserved: Characters that have no special meaning and can be used directly (A-Z, a-z, 0-9, -, ., _, ~).
• Reserved: Characters that have special structural meanings (:, /, ?, #, [, ], @, !, $, &, ', (, ), *, +, ,, ;, =). These must be encoded if used as data.

encodeURI() vs. encodeURIComponent()

In web development, choosing the right encoding method is critical:

• encodeURI(): Used for encoding a full URL. It ignores structural characters like http://, /, and ?.
• encodeURIComponent(): Used for encoding a single component of a URL (like a query parameter). It encodes almost all non-ASCII and reserved characters, ensuring data doesn't break the URL structure.

Common Encoding Examples

Security and Performance

Improper URL encoding can lead to serious security vulnerabilities such as Open Redirects or Parameter Pollution. Always encode user-provided data before appending it to a URL string. Additionally, modern browsers handle some encoding automatically, but server-side processing still relies on standardized percent-encoding for data integrity.