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This GTmetrix Online tool gives you the ability to look up the registration data for domain names. Depending on the registrar, you can see some information like who it is registered to, date of registration and expiry, where the DNS is hosted and more In some cases, you will be able to go the registrar's site to get more information.
Furthermore, if you want to buy a domain, knowing when it expires is helpful. As the date approaches the owner may want to sell or let it expire and you're right there to scoop it up.