Build a strategy game where Codex and Claude play each other
A developer built Castellan, a real-time strategy game made with Codex and Claude Code in which the players are Codex and Claude themselves.
Source
@emersoftware on X · 2026-10-20
Written in our own words. Credit to the original author. Link checked 2026-10-20.
What they did
A developer built Castellan, a real-time strategy game made with Codex and Claude Code in which the players are Codex and Claude themselves.
Result (as claimed)
He is presenting the project in a talk.
Tools they used
Cost: OpenAI Codex: free plan, paid from $8/mo; Claude Code: from $17/mo.
Set it up
Write a one-page brief
Describe the app in plain words: who it is for, the 3 core screens or actions, and what "done" looks like.
Start the project with your agent
Open OpenAI Codex and paste the brief. Ask it to propose a stack and a file plan before writing code.
Build one slice at a time
Ship the smallest working flow first, run it, then add features one by one. Commit after each working step.
Test it like a user
Click through on desktop and phone. Ask the agent to add basic tests and fix anything that breaks.
Check security and ship
Keep keys in environment variables, check auth and database rules, then deploy and share the link.
Copy the full setup prompt
Paste into your agent and it will walk you through the setup, asking before anything that sends, posts or spends.
You are helping me set up this AI use case end to end in Claude Code. Goal: Build a strategy game where Codex and Claude play each other What the original author did: A developer built Castellan, a real-time strategy game made with Codex and Claude Code in which the players are Codex and Claude themselves. Reported result (as claimed by the author): He is presenting the project in a talk. Source: https://x.com/emersoftware/status/2112390283321364541 Tools they used: OpenAI Codex, Claude Code Category: Vibe coding & apps Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
You are helping me set up this AI use case end to end in Codex. Goal: Build a strategy game where Codex and Claude play each other What the original author did: A developer built Castellan, a real-time strategy game made with Codex and Claude Code in which the players are Codex and Claude themselves. Reported result (as claimed by the author): He is presenting the project in a talk. Source: https://x.com/emersoftware/status/2112390283321364541 Tools they used: OpenAI Codex, Claude Code Category: Vibe coding & apps Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
You are helping me set up this AI use case end to end in Grok Bot. Goal: Build a strategy game where Codex and Claude play each other What the original author did: A developer built Castellan, a real-time strategy game made with Codex and Claude Code in which the players are Codex and Claude themselves. Reported result (as claimed by the author): He is presenting the project in a talk. Source: https://x.com/emersoftware/status/2112390283321364541 Tools they used: OpenAI Codex, Claude Code Category: Vibe coding & apps Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
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Guides for this use case
How to vibe code an app with Claude Code · How to vibe code a game with AI · How to run multiple coding agents together
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