URLs can only carry a limited character set, so spaces become %20 and anything non-ASCII becomes a percent-escaped byte sequence. This tool encodes and decodes in both the component and full-URI modes, which differ in whether they escape reserved characters like slashes and ampersands.
Component encoding escapes reserved characters including / ? & = #, which is correct for a single parameter value. Full-URI encoding leaves them intact so the URL structure survives.
Because HTML form submissions use the application/x-www-form-urlencoded format, where + means space. In a path segment a space must be %20; both appear in the wild.
It is converted to UTF-8 bytes first, then each byte is percent-escaped. That is why a single accented character often becomes two escape sequences.
Encoding an already-encoded string, turning %20 into %2520. It is a common source of broken links and usually means encoding was applied at two layers of the stack.
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