The best way to minify HTML online is by b using the fixcode.org HTML minifier
Fixcode.org also has the following minifiers
- CSS minifier: https://fixcode.org/minify/css
- javaScript minifier:https://fixcode.org/minify/js
- JSON minifier: https://fixcode.org/minify/json
- XML minifier: https://fixcode.org/minify/xml