Preheat oven to 375 degrees F (190 degrees C). Line a baking sheet with parchment paper.
Mix sugar, butter, egg, and vanilla together in a large bowl. Mix flour, cocoa, baking soda, and salt in a small bowl.
Beat flour mixture into sugar mixture slowly until well-combined, about 2 minutes. Stir chocolate chips into cookie dough.
Spoon cookie dough onto the baking sheet, spaced about 2-inches apart.
Bake in the preheated oven until edges are crisp, 10 to 12 minutes. Cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
