What is this?
IsValid automates statistical tests for A/B experiments. It will calculate significance and confidence intervials.
In short, you can use it to figure out what, if anything, the result of an A/B test means.
How can I use it?
I host this exact code at isvalid.org. If you want, you can host it yourself.
There is also an API (which you could host yourself!) that you can read about here.