Are free credit report websites legit?

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I'm going to be applying for a mortgage soon and I know they check your credit score. I figured before I do that, I'd like to see what my credit score is myself just in case it's bad so I can try to get that taken care of before I actually apply for the mortgage. I see commercials on TV all the time for free credit checks and all this stuff. Are those legit? Or is there some weird fine print somewhere. I'm talking about sites like this: http://www.freeannualcreditreports.org/ Is that a safe way to get a credit report or should I do something else instead? And I'm kind of new to this. Is there anything I should check besides my credit score? Thanks!