where's codex

a multiplayer 2d office lobby. 8–15 players join from their phones. nobody has a name — only a numbered pixel-art sprite. one player is codex.

wrong votes eliminate. first correct vote wins.

play:    https://wheres-codex.<jeremy>.vercel.app/?room=SGN-DEMO
qr:      generated on /projector from the web URL
trace:   https://wheres-codex.<jeremy>.vercel.app/projector?room=SGN-DEMO
ws:      https://wheres-codex.<jeremy>.partykit.dev

what it is

a turing-test party game. you and your friends walk pixel sprites around an office floor. someone in there is codex, pretending to be a hackathon attendee. you have 3 minutes 30 to spot it.

vote [07] and you're right? you win. wrong? you're a ghost — watch the rest of the round play out. nobody catches it before the timer? codex walks away and the projector shows you exactly how it pulled it off.

how it works

• codex app server is the codex agent harness exposed as a JSON-RPC stream. we feed it custom tools — say(message), move(landmark), idle() — instead of its usual coding tools. CODEX_MODEL selects the available Codex model. its reasoning is the entire reveal.
• partykit holds the room state. one durable object per room, authoritative for positions, chat, votes, and AI identity (which is never broadcast until reveal).
• the agent bridge runs on a laptop in the room. it joins as a regular numbered player, ticks every few seconds, asks a cheap cadence gate "should i reply right now?", and only fires codex when the answer is yes. you can see the laptop. you can point at it.

the codex primitive on display: app server's reasoning stream as a public surface. without it, this is "we used gpt to roleplay an npc." with it, you see the actual item/agentMessage/delta events as the round plays, in real time, on the projector. that's the demo.

how to run

pnpm install
export OPENAI_API_KEY=sk-...

# three terminals
pnpm -F party dev
pnpm -F web dev
pnpm -F agent dev

open http://127.0.0.1:5173/?room=local on a couple of phones (same wifi). open http://127.0.0.1:5173/projector?room=local&secret=$PROJECTOR_SECRET on a laptop pointed at the wall.

how it was built

codex built it. dkundel put codex into doom; we put codex into a party game. the build spec lives at SPEC.md, the operational guide for the agent at AGENTS.md, and the running progress log at PLANS.md.

credits

• characters: 16x16 base sprites (cc0)
• furniture: kenney roguelike indoors (cc0)
• font: press start 2p (sil ofl)
• everything else: codex.

shipped at the openai codex hackathon, sydney, 2026-04-29.

license

mit.