FillGood is a cooperative color-by-number game that runs in the web browser. Each picture is a grid of numbered squares, and players fill them in by picking the matching color. Selecting the wrong color has no effect, so a picture cannot be overwritten or damaged. Up to 24 players can paint the same picture at the same time in a shared room. Cursors and player names are visible live, progress is shared per player, and rooms persist so a picture can be continued later. Joining a room requires no account and no download. An optional account carries XP, levels, titles and leaderboards across devices. The game includes more than 70 pictures ranging from 16,000 to 120,000 squares, plus a daily challenge picture with its own leaderboard. When a room finishes a picture, the group votes on the next one. Further features include short cursor messages, emoji reactions, touch controls on mobile, and English and German localization.