Add the funfetti cake mix, vegetable oil, eggs, and rainbow sprinkles (if using extra ones) to a large mixing bowl. Using an electric hand mixer, mix until combined.

Chill for 30 minutes. I recommend this step since the dough is sticky and you will also get slightly puffier cookies with chilling, but you don't have to chill them. I didn't chill the cookies in the photos for the full 30 minutes.

Meanwhile, preheat your oven to 350F. Line a baking sheet with parchment paper or a Silpat non-stick mat.

Make 2" balls and place them on the baking sheet at least 2" apart, if not more since they do spread. Bake for 11-13 minutes until they're set.

Let them cool for a few minutes on the baking sheet, then transfer to a cooling rack. Once cooled, store cookies in an airtight container. 

Want to frost them? Here's the recipe for my funfetti frosting.