Open Cookie Clicker in your browser
Press F12 or Ctrl+Shift+I to open Developer Tools
Go to the Console tab
Type `Game.cookies = 999999999999;` and press Enter
Type `Game.cookiesPs = 999999999999;` and press Enter
Type `Game.gainLumps(999);` and press Enter
Type `Game.ObjectsById.forEach(o => o.amount = 1000);` and press Enter
Type `Game.UpgradesById.forEach(u => u.unlock());` and press Enter
Type `Game.Win(‘Cheated cookies taste awful’);` and press Enter
Type `Game.Earn(999999999999);` and press Enter
Type `Game.cookies = Infinity;` and press Enter
Type `Game.cookiesEarned = Infinity;` and press Enter