Here's how MasterCard's new protections will work: Sign up for a free trial and provide your MasterCard card number for your payment information. When that free trial comes to an end, the merchant will be required to send you a text or email notifying you that you will have to pay to continue the subscription. That message has to include the subscription cost, payment date and merchant name presented clearly so you know exactly who you are dealing with. The message will also have to include instructions on how to cancel in case you decide you're better off without it.
MasterCard, however, is being a bit shifty about this news. Hours after initially publishing its news about this new service, the company made a stealth edit to its blog post, which now reads: "No one wants to be unsatisfied with a physical product after paying for it. For some consumers, a free-trial is a great way to test out a new product and get comfortable with it before making a purchasing decision. And with so many merchants offering free trials for physical products, they're becoming the new norm." Both the bolded phrases were not originally in the blog post, as noted by The Verge and confirmed by a look at Google's cached version of the page. As such, it seems this protection won't help customers try digital subscriptions and not get dinged with a recurring cost if they forget to cancel.
Even if you opt to give the merchant permission to charge you so you can continue using its service, the company has to provide you with monthly receipts that show you the monthly cost. Those monthly receipts will also have to include a guide on canceling the subscription.
Update 1/17/19 3:40PM ET: This post has been updated to note that MasterCard changed its original announcement to say that this deal only applied to physical products, not digital subscriptions.