Percent-encode text for use in a URL, or decode it back. Encoding shows both variants so you can pick the right one. Runs in your browser; nothing uploaded.
Use component encoding when you're building one piece of a URL — a query parameter value or a single path segment — because it escapes the reserved characters / ? & = # that would otherwise break the URL's structure. Use full-URL encoding only on an already-assembled URL, where those characters are meant to stay. Encoding a whole URL with component encoding mangles it; encoding a value with full-URL encoding leaves & and = unescaped and breaks your query string. When in doubt, encode each value with component encoding.
Note: when decoding, a + means a literal plus here (standard decodeURIComponent); in application/x-www-form-urlencoded query strings, + historically means a space.