Credit checks are reported to the credit reporting agencies as "inquiries."
Inquiries tell other creditors that you're thinking of taking on new debt. An inquiry typically has a small, but negative, impact on your credit score. Inquiries are a necessary part of the mortgage application process, so you can't avoid them altogether, but it pays to be smart about them. As a general rule, you should apply for credit only when you need it. Applying for a credit card, car loan, or other type of loan also results in an inquiry that can lower your score, so try to avoid applying for these other types of credit right before getting a mortgage or during the mortgage process.
Shopping around for a mortgage won't hurt your credit
Within a 45-day period, multiple credit checks from mortgage lenders are recorded on your credit report as a single inquiry. This is because other creditors realize that you are only going to buy one home. You can shop around and get multiple preapprovals and official Loan Estimates. No matter how many lenders you consult, the impact on your credit will be the same as long as the last credit check is within 45 days of the first credit check. Even if a lender needs to check your credit after the 45-day window is over, shopping around is usually still worth it. The impact of an additional inquiry is small, while shopping around for the best deal can save you a lot of money in the long run. Note that the 45-day rule applies only to credit checks from mortgage lenders or brokers' credit card; other inquiries are processed separately.