When i apply for a mortgage can the lender find out how much credit i have with other lenders (on cards, etc)?

and do they know how much you are paying back a month?
Answer
Yes, mortgage lenders pull your credit report and can see your debt to income ratio and from there they can decide if they wanna lend to you or if they do how high your apr is going to be and your payment. if you have a high income to debt ratio you have more debt then what you make in a month you may wanna pay off some of your high apr cards to lower it.