# Co-op game maker: a squad of friends against the game > Describe the co-op game you want to play together. Your agent builds the missions, and Summer runs them: parties, quick play to fill the squad, and progress that carries over. - URL: https://www.summerengine.com/ja/co-op-game-maker - Keyword: co-op game maker - Related: https://www.summerengine.com/ja/online-multiplayer-game-maker A co-op game is a squad against the game. A few friends team up, quick play fills the empty seats, the mission runs on a server so everyone sees the same enemies, and the loot and unlocks carry over to the next run. Summer Engine gives you each of those pieces. Three friends form a party and press Play. Quick play adds one more player to make a squad of four. Summer starts a server for the mission, where your rules run the enemies and objectives. When the run ends, the server saves each player's rewards, so they are waiting in the next mission. You build it by asking. Your AI agent plans the game with Summer's multiplayer skills, then builds it step by step: the server and client, instant movement, server-owned enemies and objectives, squads, saved progress and mission results. ## Squads that stay together Friends form a party in the Summer app, the leader presses Play, and the whole party lands in the same mission on the same team. Quick play fills any empty seats, so a squad of four is always ready to go. ## Missions the server runs for everyone Enemies, objectives and shared resources live on the server, so every player sees the same fight. Each player moves their own character with no input delay, and the server checks every move. If someone drops out, the rest of the squad keeps playing. ## Loot and unlocks that carry over The server decides what each player earned and saves it when the mission ends, even if a player leaves early. Levels, loot and unlocks load the moment they join the next mission, on any device. ## Ratings by your own rules Give your co-op mode a rating that rises when a squad clears a mission and falls a little when it fails, with harder missions worth more. Summer records each result once and keeps the leaderboard. ## FAQ ### How do I make an online co-op game? Download Summer Engine, connect your AI agent and describe the mission and the squad. The agent builds the server and client, parties and quick play, server-owned enemies and objectives, and saved rewards. Summer runs every mission. ### Can friends always play in the same squad? Yes. Friends form a party, the leader presses Play, and the whole party lands in the same mission on the same team. Quick play fills the remaining seats. ### Does progress carry over between missions? Yes. The server saves each player's levels, loot and unlocks when a mission ends and loads them when they join the next one, on any device. ### What happens if a player leaves mid-mission? The rest of the squad keeps playing. No player hosts the game, the server keeps the mission running, and the leaving player's rewards are still saved. ### How do I test co-op without three friends? Use Local Play. It runs several players on your own computer, including a bad connection, so you can test a full squad before anyone joins. [Start building free](https://www.summerengine.com/ja/download) ## Next steps - [Online multiplayer game maker](https://www.summerengine.com/ja/online-multiplayer-game-maker): Matchmaking, parties, saves and leaderboards, hosted by Summer. - [Make a game with friends](https://www.summerengine.com/ja/make-a-game-with-friends): Plan it together on one board, then play it together. - [Co-op platformer template](https://www.summerengine.com/ja/templates/platformer/co-op-platformer): Two players, one level, every door needs both of you. - [Base-building survival template](https://www.summerengine.com/ja/templates/survival/base-building-survival): A shared base for a squad that comes back every night. --- ## Machine-readable resources - Site index for agents: https://www.summerengine.com/llms.txt - Full inlined content: https://www.summerengine.com/llms-full.txt - Porting catalog: https://www.summerengine.com/llms-porting.txt - Structured catalog: https://www.summerengine.com/agent-catalog.json - Sitemap: https://www.summerengine.com/sitemap.xml - Developer resources: https://www.summerengine.com/docs - Summer API (assets from any agent or code; public per-call model prices): https://docs.summerengine.com/api