You cannot lock a rate before getting at least pre-qualified. Lenders need your credit profile first before offering a rate lock.
A rate is meaningless without knowing your creditworthiness. Pre-qualification or pre-approval must happen first.
Pre-Qualification Required
A lender cannot offer you a specific rate until they have reviewed your credit history, income, and debt-to-income ratio. Without this information, any advertised rate is just a general market rate, not one that applies to your specific situation. The first step is always to get pre-qualified or pre-approved. For buyers in San Antonio and the Texas Hill Country, I recommend getting pre-approved before you start house hunting so you know your budget and can lock a rate when the time comes.
What Lenders Need Before Locking
To lock a rate, lenders need a completed loan application, a credit report, and preliminary verification of your income and assets. Pre-qualification gives you an estimate of what you might qualify for, but pre-approval involves a more thorough review and may allow you to lock your rate more quickly once you have a purchase contract.