All code is tested with Jasmine to keep pesky little bugs to a minimum.
Because the code is in Vanilla JS it is able to validate 100 inputs in ~15ms - that includes all visual updates.
With the minified version the code is ~11kb, with themes averaging 3kb.
Add your own testers and make them work as you want them to. Even validation via Ajax is a possibility.
To match the style of your website you can create a theme. Bootstrap3 and UIkit build-in themes are also available.
Easily translate errors to make them understandable to your end users without touching the validations.