How to use Codex to verify a deterministic tower RPG

Raymond Chan brought a playable three-floor prototype into OpenAI Build Week and used Codex to extend it into Crown Above the Veil, a ten-floor tactical puzzle RPG. The new systems included distinct build choices, deliberate backtracking, scarce resources, and a limited rewind mechanic.

Because combat was deterministic, the displayed forecast and production rules had to agree exactly. Codex worked on reducer transitions, combat traits, progression, save state, regression cases, and a resource-aware solver. That solver needed to model shops, keys, equipment, doors, rank milestones, and floor transitions rather than approving an imaginary route.

Rewind had a similar constraint: restoring position alone was insufficient. The game needed to restore the complete decision state while consuming a charge and staying consistent with autosaves. Shared authoritative data kept web, desktop, and solver behavior aligned.

Chan retained rules, balance targets, visual approval, acceptance criteria, and final review. The account reports a release-tested web and desktop game with viable routes for its build choices and deterministic replay checks. Broader blind playtesting remained future work. Automated evidence showed that a path existed; it did not answer whether every new player would find the clues fair or the backtracking memorable.

Prompt
Suggested prompt (written by Agents In Use, not the author's)

Source: Devpost · Raymond Chan