[Kirby64]

Are you… dropping cast iron cookware on the stove? I don’t know any recipe that would require some movement that would damage a glass cooktop. Cast iron cookware seems to scratch glass tops over time, but that doesn’t seem to crack or damage them (unless you drop something on it, of course).

[legitster]

I've got a large 15lb enamel dutch oven. If I am doing any sort of speedy operation where I have to scrape off crusted ingredients, I might do some real clattering about. I have some real good chicken curry recipes where I do this.

It's also worth noting that certain things like home canning might actually void the warranty of your glass cooktop. The extreme weight put on them during the process can actually put more pressure on the layers than they can handle. Older canning equipment might not even be compatible with the flat surface.

[Kirby64]

I can't speak to home canning, but again unless you're dropping cookware I don't see how rocking cookware violently back and forth is going to damage a glass top. Scratch it, sure, but not destroy it.