How do I check if my iPhone 5s is unlocked?

You can find out if your phone is locked quite easily by changing the sim card and if it comes up with sim not valid, then the phone is locked.

Doing anything to your phone online amounts to hacking it and this will void your warranty on the phone and you will not be able to get help.

If you phone is locked and you want it unlocked, then the only way to do this is via your carrier - nobody else can unlock your phone.

What happens if you put in your SIM? If you see a SIM not Valid alert, it is most likely locked to a provider.

To find out if it can be unlocked, check this article:

iPhone: About unlocking