I've noticed that nail polishes which are made to be more durable and last longer are also referred to as "nail strengtheners." I bought one like this a few weeks back. It was a colored nail polish and it was also labeled as a nail strengthener. I thought that it strengthens and colors the nails at the same time.
But later, when I checked the ingredients back home, it did not list keratin. I read the description again and realized that it's just a nail polish that's not supposed to crack or peel for a long time and is more durable.
Now I always read nail strengthener reviews and read the description and ingredients carefully before buying. Nail strengtheners are supposed to have nourishing natural ingredients in them like keratin, essential oils and so forth. If it doesn't, I know that it's not really a nail strengthener.