ive used satin ice fondant and wilton fondant and everytime i make a cake it cracks on the top edge. is this because of the fondant i use or am i doing something else wrong

Make sure you knead it very well before rolling it out. Taking too long to roll the fondant also is a factor with cracking.

I use Michelle Foster's recipe and have been very happy with it. The fondant will crack if it starts to dry out and you're still working on it. You might try adding a little (I do mean, a little) shortening and kneading it again before rolling it out. HTH

thank you so much for you help i will try this for my next cake

It also dries out if you use a lot of PS or cornstach while kneading it

I use MMF. I seem to have pretty good results. But, I don't have much to compare to because I have only used it and Wiltons. But it's much better than Wiltons.