URL encoding, also known as percent-encoding, is a process used to encode special characters in a URL string so that it can be transmitted over the internet. Certain characters, such as spaces and punctuation marks, are not allowed in URLs and must be replaced with a percent symbol and a two-digit hexadecimal value representing the character's ASCII code.

URL encoding is necessary because certain characters in a URL string are not allowed and can cause errors when transmitted over the internet. Encoding these characters ensures that the URL can be transmitted without causing any problems.

The URL Encoder/Decoder tool works by converting special characters in a URL string into their corresponding percent-encoded representation and vice versa. To use the tool, simply paste your URL into the input field and click the "Encode" or "Decode" button. The tool will then perform the conversion and display the result in the output field.

You can encode or decode a URL in JavaScript using the built-in encodeURIComponent and decodeURIComponent functions. These functions will replace any special characters in the URL with their percent-encoded representation and vice versa.