Repository: https://github.com/Composio-HQ/polymarket-kalshi-arbitrage-bot
15-minute market trading bot that detects price differences between Polymarket and Kalshi and decides when to buy on Polymarket based on configurable rules.
- Real-time detection: Fetches UP/DOWN (Yes/No) token prices from both Polymarket (CLOB) and Kalshi (orderbook + market status) on a configurable interval.
- Start window: The bot only evaluates buy signals after 8 minutes (configurable) from market start time.
- Buy rules:
- Spread rule: When Kalshi’s YES price is in the 93–96¢ range and Polymarket’s UP token is at least 10¢ cheaper (or equal), the bot signals buy on Polymarket.
- Late resolution: If Kalshi has finished (closed/settled) but Polymarket is still open and has liquidity, the bot signals buy on Polymarket (arbitrage on timing difference).
- Express + TypeScript
- Axios for Polymarket and Kalshi HTTP APIs
- @polymarket/clob-client + ethers for placing Polymarket orders (when trading enabled)
- dotenv for configuration
npm install
cp .env.example .env
# Edit .env: set MARKET_START_TIME, KALSHI_TICKER, POLYMARKET_TOKEN_UP, POLYMARKET_TOKEN_DOWN, POLYMARKET_PRIVATE_KEY, POLYMARKET_PROXY_WALLET_ADDRESS
npm run build
npm startFor development with auto-reload:
npm run dev| Variable | Description | Example |
|---|---|---|
PORT |
Server port | 3000 |
POLL_INTERVAL_MS |
How often to fetch prices (ms) | 5000 |
MARKET_START_TIME |
Market start (ISO 8601); used for “after 8 min” window | 2025-02-19T15:00:00.000Z |
START_DELAY_MINS |
Minutes after start before evaluating | 8 |
KALSHI_API_BASE |
Kalshi API base URL | https://api.elections.kalshi.com/trade-api/v2 |
KALSHI_TICKER |
Kalshi market ticker for this 15-min market | KXHIGHNY-24JAN01-T60 |
POLYMARKET_CLOB_BASE |
Polymarket CLOB base | https://clob.polymarket.com |
POLYMARKET_TOKEN_UP |
Polymarket token ID for UP (Yes) | (from Polymarket market page) |
POLYMARKET_TOKEN_DOWN |
Polymarket token ID for DOWN (No) | (from Polymarket market page) |
KALSHI_MIN_CENTS |
Min Kalshi YES price for spread rule | 93 |
KALSHI_MAX_CENTS |
Max Kalshi YES price for spread rule | 96 |
MIN_SPREAD_CENTS |
Min spread (Kalshi − Polymarket) to signal buy | 10 |
POLYMARKET_PRIVATE_KEY |
EOA private key | 0x... |
POLYMARKET_PROXY_WALLET_ADDRESS |
Gnosis Safe / proxy wallet address | 0x... |
POLYMARKET_CHAIN_ID |
CLOB chain (Polygon = 137) | 137 |
POLYMARKET_TRADE_USD |
USD amount per buy order | 10 |
POLYMARKET_BUY_COOLDOWN_SECONDS |
Min seconds between buy orders | 60 |
- GET /health – Health check.
- GET /status – Last Polymarket and Kalshi prices, current arbitrage signal, whether trading is enabled, and whether the start window has passed.
- POST /poll/start – Start the price polling loop (default: starts automatically).
- POST /poll/stop – Stop the polling loop.
action: "buy_polymarket"– Buy on Polymarket (spread rule); includeskalshiYesCents,polymarketUpCents,spreadCents.action: "buy_polymarket_late"– Buy on Polymarket (Kalshi finished, Polymarket still open); includeskalshiStatus.