I turned Pokémon Red into a shared multiplayer arcade — here's how

🎮 Play it live → — one instance, everyone plays together.

the idea started simply: what if visitors to my site could play Pokémon Red together, passing the controller between them like a Twitch Plays setup — but embedded on a blog, backed by a proper save state, and with no server cost worth mentioning?

this is the full build log.

what it does

one copy of Pokémon Red runs in the browser. anyone who opens the page can join. a single player holds the controller at a time; after five seconds idle the turn passes to the next person in queue. if nobody is around, an AI bot picks up and navigates the overworld or battles. there is a live chat next to the game. the save state persists across sessions: close the tab, come back tomorrow — the game is exactly where you left it.

step 1 — build the ROM from source

everything starts with pret/pokered, the fully reverse-engineered disassembly of Pokémon Red and Blue. it's a remarkable project: decades of community work turned a 1 MB Game Boy cartridge into readable, annotatable assembly.

bashgit clone https://github.com/pret/pokered.git
cd pokered
make
# produces pokered.gbc
sha1sum pokered.gbc   # verify against roms.sha1

you need rgbds (≥0.9). the assembler, linker, and fix tool are all included. make produces pokered.gbc — a verified cartridge image. the SHA1 is pinned in roms.sha1; build reproducibility matters when you're going to ship this ROM publicly.

step 2 — compile the emulator to WebAssembly

binjgb is a cycle-accurate Game Boy emulator written in C. it is small, well-structured, and exposes the right hooks for Emscripten compilation.

bashgit clone https://github.com/nicknassar/binjgb.git
source ~/emsdk/emsdk_env.sh

emcc binjgb/src/emulator.c binjgb/src/joypad.c binjgb/src/apu.c \
     web/binjgb/wrapper.c \
     -o dist/binjgb.js \
     -s EXPORTED_FUNCTIONS=@web/binjgb/exported.json \
     -s MODULARIZE=1 \
     -s ALLOW_MEMORY_GROWTH=1 \
     -O3

web/binjgb/exported.json lists the eight C functions the browser shell needs:

json["_emulator_new_simple", "_emulator_run_until_f64",
 "_get_frame_buffer_ptr", "_get_audio_buffer_ptr",
 "_emulator_get_ticks_f64", "_free",
 "_malloc", "_joypad_set"]

wrapper.c is an overlay that adds a frame-perfect 60fps canvas loop and exposes the audio ring buffer to JavaScript without modifying binjgb's source. the compiled output is two files: binjgb.js (runtime and glue) and binjgb.wasm (the actual bytecode).

step 3 — wire the browser shell

web/player.html is a standalone HTML page. no framework, no bundler. it loads binjgb.js, initialises the emulator with the ROM bytes, then ticks forward in a requestAnimationFrame loop.

the loop is straightforward:

javascriptfunction tick(now) {
  const cyclesPerFrame = 4194304 / 60;
  Module._emulator_run_until_f64(emulatorPtr,
    Module._emulator_get_ticks_f64(emulatorPtr) + cyclesPerFrame);
  renderFrame();
  scheduleAudio();
  requestAnimationFrame(tick);
}

keyboard input goes through a thin dispatcher in player.js that maps DOM KeyboardEvent codes to the eight Game Boy buttons and calls Module._joypad_set. the canvas is upscaled 3x with nearest-neighbour interpolation so the pixel art stays crisp.

step 4 — the multiplayer turn system

the most interesting engineering is the turn system. it lives in two files: web/multiplayer.js (browser client) and server/server.js (Node.js WebSocket server deployed on Railway).

the protocol is minimal:

the server tracks one activeMode: idle, human, or ai. only the mode holder's inputs are forwarded to the emulator. everyone else spectates.

turn timer:

javascriptfunction resetTurnTimer(ws) {
  clearTimeout(turnTimer);
  turnTimer = setTimeout(() => {
    if (activeMode === 'human' && activePlayer === ws) {
      revokeHumanTurn();
      grantNextOrIdle();
    }
  }, TURN_MS); // 5000
}

every button press from the active player resets the five-second timer. idle means someone gets granted next. a human leaving means the next person in queue or idle. idle long enough means the AI gets a turn.

step 5 — persisting save state with Redis

without persistence the game would restart every time the server restarts or the last player leaves. the solution: serialize the full emulator RAM and store it in Redis on every turn handoff.

javascript// on turn handoff (server.js)
const stateBlob = emulator.serializeState();      // ~8 KB base64
await redis.set('pokemon:state', stateBlob);

// on new player joining
const saved = await redis.get('pokemon:state');
if (saved) ws.send(JSON.stringify({ type: 'state_sync', state: saved }));

upstash redis is serverless: no persistent connection, no provisioning. the REST API fits perfectly with Railway's ephemeral container model. the free tier covers ~10 000 requests/day — more than enough at hobby scale.

step 6 — the AI bot

autoplay.js is a simplified port of bouletmarc/PokeBot. the bot doesn't do screen scraping; it reads Game Boy RAM addresses directly via the emulator's exported memory pointer.

javascript// check if we're in a battle
const BATTLE_ACTIVE = 0xD057;
const inBattle = readRam(BATTLE_ACTIVE) !== 0;

if (inBattle) {
  battleRoutine();   // select FIGHT, pick highest-PP move
} else {
  overworldWalk();   // random walk with wall-bounce detection
}

the bot is gated by multiplayerAllowed: it only activates when the server has granted it a turn via ai_granted. it never fires when a human holds the controller.

step 7 — embedding or self-hosting

embed the shared arcade (one line):

html<iframe src="https://yigitkonur.github.io/wasm-pokemon-red/"
        width="100%" height="640"
        style="border:none;border-radius:12px"
        allow="autoplay">
</iframe>

self-host the whole stack:

1. clone yigitkonur/wasm-pokemon-red and build the ROM and WASM (make)
2. deploy server/server.js to Railway — one-click from railway.toml
3. create an Upstash Redis instance, set UPSTASH_REDIS_REST_URL and UPSTASH_REDIS_REST_TOKEN in Railway environment
4. update WS_URL in web/multiplayer.js to point to your Railway deployment
5. push web/ to any static host (GitHub Pages, Netlify, Vercel, S3)

total cloud cost at hobby scale: $0.

what's next

the logical next step is more ROMs. the binjgb emulator handles any Game Boy cartridge; swapping the ROM file and redeploying is a five-minute operation. the turn system, Redis persistence, and AI bot are all ROM-agnostic.

the interesting design question is whether to run each ROM as a separate page with its own server, or to extend the server to a multi-room model where each room is one ROM. the latter is more elegant and would let visitors channel-surf between games — like a small arcade.

Tetris is the obvious first addition. Link's Awakening next. eventually a lobby page at the root where you pick a game, join the queue, and play for your five seconds.

links

• live arcade: yigitkonur.github.io/wasm-pokemon-red
• source: github.com/yigitkonur/wasm-pokemon-red
• pret/pokered: github.com/pret/pokered
• binjgb: github.com/nicknassar/binjgb
• PokeBot: github.com/bouletmarc/PokeBot