Preheat the oven to 325 degrees F. Whisk together the flour, cocoa powder, baking soda and salt; set aside. In a medium bowl, cream together melted butter, brown sugar and white sugar until well blended. Beat the vanilla, and eggs until light and creamy. Mix dry ingredients until stir just until blended. Stir in the chocolate chips. Scoop 1/4 cup dough and place on greased cookie sheets. Make sure to leave space between cookies to leave room for spreading. Bake for 14 to 16 minutes in the preheated oven, or until the edges are lightly browned. Let set for a few minutes before transferring to a wire rack.