URL Encoder / Decoder
URL-encode and decode text with encodeURIComponent or encodeURI semantics, with clear errors for malformed input.
How to use
Pick a mode, then Encode or Decode. Component mode matches encodeURIComponent: it escapes everything including separators like & and =, which is what you want for a query parameter value. Full URL mode matches encodeURI: structural characters such as :// and ? are left intact.
Notes
Everything runs in your browser. Decoding input with an invalid percent-escape such as "%ZZ" shows an error. Note that "+" is not converted to a space here — that rule belongs to application/x-www-form-urlencoded form bodies, not to percent-encoding itself.
FAQ
How is non-ASCII text encoded?
As UTF-8 bytes, percent-escaped. For example "あ" becomes %E3%81%82.
Which mode should I use?
Component mode for a piece of a URL (a search term or parameter value), Full URL mode for a complete URL.