Turn text into something safe to put in a query string, or take a URL full of %20 and read what it actually says.
This page loads no libraries at all — the work is done by the browser itself.
Your file is read on your own machine and never sent anywhere — open your
browser's network tab and watch while you use it.
Questions
Which characters get encoded?
Everything except letters, digits and a small set of symbols that URLs already allow. Everything else becomes a percent and two hex digits.
Why does decoding fail sometimes?
A stray % that is not followed by two hex digits makes the whole string invalid.
Other text & code tools
Everything here is free and works the same way — in your browser.