URL Encoder

Percent-encoding replaces a character with % and its byte value in hex, so that characters which would otherwise be read as structure can appear inside a URL as data. Which characters those are depends entirely on where in the URL the value is going, which is why this tool asks rather than picking one.

Component or whole URI

Component escapes the delimiters — &, =, ?, /, # — so the result is safe as a single query value or path segment. Use it for anything you are putting into a URL.

Whole URI leaves those delimiters intact and escapes only what is never legal, such as spaces. Use it when the input is already a complete URL whose structure you intend to keep. Encoding a whole URL in component mode turns its structure into literal text; encoding a value in whole-URI mode leaves an & free to split the query in two. Both mistakes are common and both are silent.

Form data: + or %20

Form data is application/x-www-form-urlencoded, the format an HTML form submits and URLSearchParams produces. It writes a space as + rather than %20, and escapes ~, which RFC 3986 leaves alone. Use it for a query string a server will parse as form fields; use component mode anywhere else, because outside form data a + is a literal plus sign.

Non-ASCII

Encoded as UTF-8 octets, one %XX per byte — which is why é becomes %C3%A9 rather than a single escape. RFC 3986 requires this and servers expect it.

a&b=c in component mode becomes a%26b%3Dc, which survives as one query value. In whole-URI mode it comes back unchanged — correct for a URL, wrong for a value. Reverse either with the URL Decoder.