About URL encoding
URLs can only contain a limited set of ASCII characters. Special characters like spaces, ampersands and non-ASCII letters must be percent-encoded — replaced with a percent sign followed by two hexadecimal digits representing the character's byte value. For example, a space becomes %20 and the letter a-umlaut becomes %C3%A4.
This tool uses encodeURIComponent, which encodes everything except letters, digits and the characters - _ . ! ~ * ( ). It is the correct function to use when encoding a query string parameter value or a path segment, not an entire URL.