Caro

Caro (Gomoku / five-in-a-row) on a 20×20 board, with a local engine you can play against or pit against itself.

Play against the computer, let the computer play first, or run a multi-board Tournament where every difficulty pairing races in parallel.

Quick start

npm install -g caro-tournament
caro-tournament

Or without a global install:

npx caro-tournament

This starts a local server at http://localhost:2026 and opens it in your browser. Game data is stored under ~/.caro-tournament/.

Useful flags:

caro-tournament --port 3000   # use a different port
caro-tournament --no-open     # start server without opening the browser

Tournament

Tournament mode matches the four difficulty levels against each other: easy, medium, hard, and expert.

• Seat order matters. Hard going first against medium is a different match from medium going first against hard, because the opening move is an advantage.
• You can run several boards at once so pairings play in parallel. The page stays responsive while games run.
• When games finish, results are saved. Open Results to see wins, draws, and average move counts for each pairing and overall.

Entering Tournament sets up the boards but waits: pick how many boards to run, then click Start. Click the board tabs to watch each game, or the Results tab for the standings.

Practice

Practice mode looks like Tournament — computers play each other across parallel boards — but the goal is training, not standings.

• Every board writes to a shared experience cache on disk, so the engine gets stronger the more it plays.
• Results are not recorded; there is no Results tab.
• A game restarts automatically once both players leave known experience, so practice explores more openings.

As with Tournament, pick how many boards to run and click Start, then click the tabs to watch individual games.

The engine

The engine is the computer opponent behind every computer-controlled seat. Strength is controlled by difficulty:

• Easy: Shallow look-ahead, quick replies, more variety in play
• Medium: Deeper search and recognition of common traps
• Hard: Longer thinking time and full awareness of fork patterns
• Expert: The strongest profile, with extra time and forced-line hunting

Higher levels think longer and see more of the board. Lower levels move faster and play with more unpredictability.

Develop from source

Requirements

• Node.js 18+ (developed on Node 24)
• npm (comes with Node)

Install

npm install

Build & start

npm start

# Custom port, no browser
npm start -- --port 3000 --no-open

This builds the app and starts the same local server (port 2026, opens the browser).

Useful scripts:

| Command | What it does | | ------------------- | ----------------------------------------------- | | npm start | Production build and serve on port 2026 | | npm run dev | Dev build (debug on) and serve on port 2026 | | npm run build | Build UI (dist/ui) and CLI | | npm run dev:ui | Vite HMR for the UI (proxy /api to port 2026) | | npm test | Run tests | | npm run typecheck | TypeScript check | | npm run lint | Lint |

Open the page, pick a mode (you first, computer first, or Tournament), choose difficulty or board count, and play - or watch the computers compete.

License

This project is licensed under the GNU Affero General Public License v3.0 (AGPL-3.0).

You may use, modify, and share it, but if you distribute it or run a modified version as a network service, you must make the corresponding source available under the same license.