Cross-Platform Arb Scanner

What Is the Cross-Platform Arb Scanner?

The Arb Scanner is a live arbitrage detection tool that scans Kalshi and Polymarket simultaneously for the same event priced differently. When Kalshi says 55% and Polymarket says 42%, one of those prices is wrong. The scanner finds that gap automatically and tells you if it's large enough to trade.

Unlike manual comparison, the scanner normalizes prices across both platforms, matches markets describing the same event using title similarity (Jaccard similarity), and scores every matched pair using symmetric KL divergence — a measure of how inconsistent two probability distributions are.

How It Works

Run the scanner and it fetches live data from both Kalshi and Polymarket. Matched pairs scoring above 0.05 (WATCH) or 0.15 (ARB FLAGGED) are surfaced immediately with direct trade links to both platforms. The scanner does not save state — every run reflects live prices.

When to Use This Tool

Use it when you want to check for executable arb opportunities across Kalshi and Polymarket before placing a trade. Check the scanner at market open, after major news events, and before any contract with high volume on one platform. Pair with the EV Calculator and Kelly Criterion to size any flagged position. Pro subscribers get direct trade links and real-time refresh.

How the scanner works

The scanner fetches live markets from Kalshi and Polymarket every time you run it. It normalizes all prices to implied probability, then runs a fuzzy title-match algorithm (Jaccard similarity) to identify markets describing the same event on both platforms. Any pair with a match score above 15% gets scored for price divergence using symmetric KL divergence.

KL divergence measures how inconsistent two probability distributions are — not just the raw price gap. A 10¢ gap at 50/40 behaves very differently than a 10¢ gap at 90/80. KL captures this. Markets scoring above 0.15 get flagged as potential arb opportunities.

What to do when you see ARB FLAGGED

First: verify that both markets resolve on the same event, on the same date, with compatible terms. Kalshi and Polymarket sometimes phrase questions differently even when they're describing the same event. Second: check bid-ask spreads on both sides — a flagged arb with wide spreads may not be executable at the displayed midpoint. Third: check liquidity. If one side has thin order books, your fill price will differ from the displayed probability.

If all three checks pass, the trade is straightforward: buy YES on the cheaper platform and hedge on the more expensive one, or leg into both YES positions if the combined cost is under $1.00.