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.

This is 90% profitable logic, 100% profitable logic version 2 in sale! 🤞

How it works

• 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:
  1. 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.
  2. 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).

Stack

• Express + TypeScript
• Axios for Polymarket and Kalshi HTTP APIs
• @polymarket/clob-client + ethers for placing Polymarket orders (when trading enabled)
• dotenv for configuration

Setup

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 start

For development with auto-reload:

npm run dev

Configuration (.env)

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

API

• 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.

Signal format

• action: "buy_polymarket" – Buy on Polymarket (spread rule); includes kalshiYesCents, polymarketUpCents, spreadCents.
• action: "buy_polymarket_late" – Buy on Polymarket (Kalshi finished, Polymarket still open); includes kalshiStatus.