PaperDrill is a live paper-trading exchange simulator with a real matching engine and order book. Trade through the web interface or connect a bot through the API—no KYC and no real funds at risk.
- Live matching engine — price-time priority matching rather than mocked fills.
- Real-time market data — order book, trades, tickers, and updating candles over WebSocket.
- Persistent accounts — simulated balances, open orders, order history, and trade history.
- Public leaderboard — compare simulated portfolio performance with other traders.
- Scoped API keys — programmable account access and order management.
- Bot-friendly API — REST trading endpoints and public WebSocket feeds.
- Daily simulated credit — idempotent recurring credit with an adjustable PnL baseline.
| Service | Responsibility |
|---|---|
frontend |
React SPA for markets, trading, account management, docs, and leaderboard |
backend |
Express REST/WebSocket API, authentication, validation, and market metadata |
engine |
In-memory balances, order books, matching, and periodic snapshots |
worker |
Persists orders/fills and derives candles and tickers |
bot |
Optional market makers for the supported markets |
| PostgreSQL | Accounts, markets, orders, fills, candles, credits, and leaderboard data |
| Redis | Commands, responses, event streams, pub/sub, and runtime checkpoints |
Backend, engine, and worker communicate through Redis. Production uses an external PostgreSQL provider; Redis and engine snapshots use persistent Docker volumes, with nginx running on the application host.
| Layer | Technology |
|---|---|
| Runtime | Bun + TypeScript |
| Frontend | React 19, Tailwind CSS 4, TanStack Query |
| API | Express 5, WebSocket (ws), Zod |
| Data | PostgreSQL/TimescaleDB, Prisma 7, Redis 7 |
| Observability | Structured service logs, Sentry, PostHog |
| Infrastructure | Docker Compose, nginx, GHCR, Cloudflare |