Encode and decode URLs

URLs may only contain a restricted set of characters. Anything outside it, including spaces, non-English letters, and the characters that give a URL its structure, has to be written as a percent sign followed by two hexadecimal digits. That substitution is what percent-encoding means.

The choice that decides whether the result works is which of two jobs you are doing. Escaping a single value, such as a search term going into a query parameter, has to escape ampersand and equals, because leaving them alone lets one value pretend to be several parameters. Escaping a complete address must not touch those same characters, or the slashes and colon that hold the address together are destroyed. Picking the wrong one is the usual reason an encoded link stops resolving, so the choice is presented directly rather than hidden.

Decoding reverses either form. A string that contains a bare percent sign, such as a copied line with a discount figure in it, is not valid percent-encoding, and the tool explains that rather than failing without a reason.

URLs pasted into a converter regularly carry session identifiers, signed download links, or internal hostnames. Conversion happens in the browser for the same reason the rest of the site works that way: the address never needs to reach anyone else for the escaping to be worked out.