I'm not a specialist, but as far as I know, a bit of information in a QR-code is coded more than once, and it is defined as the redundancy level
How can I estimate a QR-code redundancy level ? Is where an mobile app or a website where I can test my QR-code redundancy level easily ? If not, is it an easy algorithm that I can implement ?
Redundancy is sorted in different categories according to this website, but I'd like to have the direct percentage value if possible
There are some pixels next to the lower left positioning block which indicate the redundancy level. Quote from https://blog.qrstuff.com/2011/12/14/qr-code-error-correction
Quite conveniently, there’s also 2 modules down in the bottom left-hand corner of every QR code that display what the error correction level used in that QR code is.
There is a very nice graphic on that page which visualizes this, which I won't include here as I assume that I'm not licensed to do so.