Show: 2D game built using Codex and agent skills (zero code)

Codex Codex CLI
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Hi everyone!

After previously building a “flat” little 2D sandbox game level using Codex CLI and agent skills, I decided to truly step into a role of an agentic game designer and orchestrate a fully playable game level (once again, with Codex and agent skills). This time with all the bells and whistles! Tiles, enemies, sounds, music!

You can play the game here.

I also documented everything (and you can clone and run locally) here.

I know you love takeaways, so I’m going to give you some takeaways:

  • This was one of the most enjoyable experiences ever!
  • Applying harness engineering with progressive disclosure is incredibly powerful - I treated my SKILL.md as simply a ToC (a “skills map”) and took it from there
  • Implement -> Evaluate loops are key - I used Playwright and an evaluation checklist and the agent built and corrected automagically
  • I used PROGRESS.md as a memory/log mechanism for the agent, and a way to minimize context noise
  • The game dev agent was steered by the DESIGN-DOCUMENT.md, stipulating game objectives, layout and mechanics
  • I used progressive prompting - I built up the game piece wise - starting with basic player mechanics, then adding tiles, NPCs, interactions, sounds, menus - one prompt at a time

Zero code written by me. Never even looked at the game engine (Phaser) API - just gave the skills a link to the documentation. The future is here!

Credits to ansimuz (gothicvania assets) and Pascal Belisle (music).

If there is interest I can turn this into an OpenAI Cook Book.

@PaulBellow

Some screenshots below:

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image2344×1550 216 KB

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image2344×1550 216 KB

8 Likes
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Need to note how to move the player using WASD keys

  • A - Left
  • D - Right
  • W - Jump
  • S - Squat

On Chrome on Windows 11, a mouse or the arrow keys did not work.

I see it now, silly me. (Captured from Video)

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When I first start the game this is how it shows

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Yes sorry, I used small pixel font, I can fix it, but also I can add standard direction keys and maybe space bar for action, that’s silly of me actually (I mapped things to my keyboard, which is tiny and direction keys are not great)

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Nothing to apologize for.

When I read this, I thought it could easily rank among the top topics of value on this forum. We need more topics of this caliber.

I’m simply aiming to help others and offer feedback that you genuinely find useful.

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Ok I updated the game so it uses directional keys and space (for attack), besides the W/A/S/D; also now you can actually finish the level :-). Thank you Codex!

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Looks great! Thanks for sharing.

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If you take it to production and sell remember you can’t use the Castlevania sounds =D

That said, it’s one of the smoother scrollers and platformers I’ve seen yet.

Great Job!

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Tremendous, good job! I implement something similar, but using it as an assistant to program and lead the project in Unity.

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