Paste the string into a browser-based URL encoder and it percent-encodes every character that is not safe in a URL, so a space becomes %20 and an ampersand becomes %26. The encoding runs locally in your browser, so query values containing emails, tokens or search terms are never sent anywhere.
Characters like ?, &, = and # have structural meaning in a URL, so putting them raw inside a query value corrupts the request: everything after a stray & is read as a new parameter. Percent-encoding, defined in RFC 3986, replaces each unsafe byte with % followed by its hex value, which is why a properly encoded parameter survives any URL intact.
The classic mistake is encoding an entire URL, which mangles the :// and the path slashes. The rule is to encode each component, typically each query parameter value, on its own, the way JavaScript's encodeURIComponent does. A tool that encodes and decodes both directions also makes it easy to unpack an existing URL and see what a garbled parameter actually contains.
The standard from RFC 3986 that replaces unsafe characters with % plus their hex value, for example a space becomes %20.
No. Encode each component, such as an individual query parameter value. Encoding a full URL breaks its structure.
No. Encoding and decoding happen entirely in your browser.