URL encoding, also known as percent-encoding, is a mechanism defined in RFC 3986 for representing special characters 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 -- or characters that have special meaning in a URL -- must be replaced with a percent sign (%) followed by two hexadecimal digits representing the character's byte value. For example, a space becomes %20, an ampersand becomes %26, and a forward slash becomes %2F.
URLs use certain characters as delimiters: ? separates the path from the query string, & separates query parameters, = assigns values to parameters, and # marks the fragment identifier. If your data contains any of these reserved characters, failing to encode them will break the URL structure and cause unexpected behavior. Non-ASCII characters such as accented letters, Chinese characters, or emoji also require encoding to be safely transmitted. The difference between encodeURI and encodeURIComponent matters: the former preserves URL structure characters while the latter encodes everything except letters, digits, and a few safe symbols, making it the right choice for encoding individual parameter values.
URL encoding is essential when building query strings for API requests, constructing redirect URLs, passing user-generated content as URL parameters, or creating share links that include titles or descriptions. Web developers use it to safely embed file paths with spaces, handle internationalized domain names, and encode form data submitted via GET requests. This tool lets you quickly encode or decode URL strings directly in your browser without sending your data to any server, making it ideal for debugging API calls, testing webhook URLs, and constructing complex query parameters.