A pile of chocolate chip cookies
The Reason You Should Never Use Aluminum Foil When Baking Cookies
It's common to use aluminum foil to bake, but you should never use it when baking cookies, and for good reason. Aluminum foil will cause your cookies to bake unevenly.
Since aluminum foil is a heat conductor, the bottom of the cookies will receive more heat and bake faster. It will leave you with crispy bottoms and not-quite-done middles.
In a worst-case scenario, the bottoms of your cookies may even burn while the rest of them don't thoroughly bake through — definitely not ideal.
Next time you bake cookies, use parchment paper or silicone baking mats since they prevent sticking and distribute heat evenly. Greasing a baking sheet also works just fine.