Is this online checker tool safe to use?

This service is safe to use. The only risk is if anyone is literally looking at your screen while you use the website.

We can't and won't access any of the data you insert in the website, including you credit card number. All the computations are performed in your browser so that your credit card number remains safely with you.

If you are technically inclined you can look behind the scenes and make sure that absolutely no contact is being made with our server, no cookies are being set, no local storage is being used. If you're not technically inclined, ask politelly to a friend who is, and make sure!