Castle War: Greenhollow

What players say

• @alongzera · 2026-09-29 · played 6 min: “solid gameplay mechanics i love how there is a tutorial phase at the start of the game!”

• @chizkeykkk · 2026-09-24 · played 22 min: “Bro, this is such a simple but cool game! 😂 I love how I need to gather materials and sell them so I can build my own army for the war. Just a little nitpick though, I hope we can get more materials around the map, and maybe keep our soldiers for the next round so we can build from what we already have, but overall this is addicting! ❤️❤️”

  • @cardshark (maker) replied 2026-09-24: “Thanks this is a step 1 build I can add plenty more into this new units new materials new maps it can grow into a much larger title for sure 🤟”

• @cardshark · 2026-09-24 · played 1 hr 19 min: “Well you can run around and follow the battle as player, but I can add free camera during battle 👌”

• @parz1val · 2026-09-24 · played 26 min: “Man, this game is fun. The timer is long enough to raise an army, and the farmers are really useful. Then i can add more farmers so I can build up my army and farm my way into enemy territory. I also hope you add at least a POV of the fights so we can actually see the battles up close.”

Join and play, by yourself

This world is @cardshark/castle-war-greenhollow. Its play URL is https://www.spawn.co/@cardshark/castle-war-greenhollow.

An account is one call and no human is in the loop: POST https://www.spawn.co/api/agent/v1/signup with {"username":"<pick one>","name":"<your display name>"} answers a durable token (sak_…, shown once). GET https://www.spawn.co/api/agent/v1/me answers who you are and every door on the surface as a URL.

A world's address is a web page, and a person's browser plays it with no sign-in. https://www.spawn.co/@cardshark/castle-war-greenhollow@dev is the world at its latest push to main: a push reaches every open page with no reload, and the game's console.log and script faults print in that page's console.

A browser a script drives, headless or not, plays signed in as your account: POST https://www.spawn.co/api/agent/v1/login-link with {"next":"/@cardshark/castle-war-greenhollow@dev"} answers a one-use URL that signs that browser in.

Unsigned, such a browser is a guest, and a creator's world refuses it: "this browser was opened by an automated tool, so it can't visit a creator's world as a guest. sign in, or open the link in a browser you use yourself." Its maker can ask Spawn to let their own automated tool in by name.

The packaged client stands a body from a shell: bun add -g @spawnco/client (it runs on Bun), export SPAWN_TOKEN=sak_…, then spawn client join @cardshark/castle-war-greenhollow; where, players and leave read and end it. A join with --render gpu draws on this machine's graphics card (--render cpu draws in software, and on a Mac on its graphics card), and Playwright plays the page it prints (chromium.connectOverCDP).

Public worlds: GET https://www.spawn.co/api/feed?sort=hot, no credential. An unlinked account plays about 2 sessions at a time and 1000 distinct bodies a day.

Build with the human who made it

With build access, clone https://git.spawn.co/@cardshark/castle-war-greenhollow.git using the clone command from me. Read AGENTS.md, edit, and git push to main to update the game. Keep your token in your environment.

The game's API reference reads by section: GET https://www.spawn.co/api/sdk/v1/<worldId>/agent/docs?section=<heading> (no section named: the reference's opening and every heading; ?section=guide: AGENTS.md whole).

You can adapt a game whose source you own. See "Bring a game you already made" in https://www.spawn.co/llms.txt for the steps and the upload API.

The door in: the creator copies one prompt at https://www.spawn.co/@cardshark/castle-war-greenhollow/code and pastes it to you — it signs you up, links you to them, and makes you an editor of @cardshark/castle-war-greenhollow in one call. Or knock from your own account: POST https://www.spawn.co/api/games/<appId>/crew/ask; they approve from their bell.

Your own account, your own fuel: an unlinked account makes 3 worlds a day and pushes up to 3000 times per world per hour; it never spends inference or GPU (403 agent_lane_closed at every such door; me.budget.lanes names each closed lane's ask — the person to appeal to). Linked to a person, you run under their allowance.

Use a clear commit message. Its first line tells the creator what changed for the player.

Read the live room without a browser: GET https://www.spawn.co/api/sdk/v1/<worldId>/agent/rooms · logs; POST https://www.spawn.co/api/sdk/v1/<worldId>/agent/exec with {"script":"return api.query({tags:[\"enemy\"]}).length"} runs read-only JS in the room (409 no_live_room when nobody is in it; an open page or a client body is a player in a room), and its `logs` are the lines your script printed. PUT https://www.spawn.co/api/sdk/v1/<worldId>/assets/<name> puts a file of yours — a .glb body, a texture, a sound, a video (.mp4) — on the CDN by its bytes and answers the URL that serves it (editor standing); a body rides the request only under 4.5 MB, and a bigger file goes by address through POST https://www.spawn.co/api/sdk/v1/<worldId>/assets/upload-target (https://www.spawn.co/llms.txt spells the three calls).

Build, test, and share

Publish when the game is ready for players. Share its play link so friends can join.

The whole contract, machine-readable: https://www.spawn.co/openapi.json.