This tool percent-encodes text so it can travel safely inside a URL. Characters that have special meaning, or that are simply not allowed in a web address, are replaced by a percent sign followed by two hexadecimal digits, and the encoded result appears in the right editor the moment you type or paste into the left one.
The toolbar dropdown offers two modes. Component mode encodes everything with reserved meaning — including &, ?, =, and / — which is what you want when inserting a value into a query string or path segment, such as a search term or a redirect URL passed as a parameter. Full URI mode leaves structural characters like ://, ?, and & alone, so an entire URL stays intact while spaces and non-ASCII characters still get escaped.
Percent-encoding here is handled by code running purely on your side of the connection. The site never sees the URLs or text you encode — there is no upload step and no inspection of your input — so addresses containing session IDs, e-mail addresses, or internal hostnames stay strictly on your computer.
Use component mode when the text will become one piece of a URL, like a query parameter value; it encodes &, =, ?, and / so they cannot break the surrounding structure. Use full URI mode when you already have a complete URL and only want illegal characters such as spaces escaped without destroying the address.
Spaces are not permitted in URLs, so they are escaped as %20, the hexadecimal value of the space character. You may also see + used for spaces, but that convention belongs to HTML form encoding, not general-purpose URL encoding.
They are first converted to UTF-8 bytes, and each byte is then percent-encoded separately. An accented e becomes %C3%A9, and a single emoji can expand to four escaped bytes, which is why non-ASCII text grows substantially when encoded.