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 by title-token coverage, and scores every matched pair on the raw price gap — the difference in implied probability between the two platforms — with a symmetric KL-divergence reading shown alongside as a secondary signal.

How It Works

Run the scanner and it fetches live data from both Kalshi and Polymarket. Matched pairs with a gap above 3pp (WATCH) or 6pp (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 title-match algorithm — scoring the share of the shorter title's content words that appear in the longer one, with year/month guards so markets about different dates never pair — to identify the same event on both platforms. Any pair that clears 60% token coverage gets scored on its price gap: the raw difference in implied probability.

A pair priced ~6 percentage points apart or more gets flagged as a potential arb. The scanner also shows a symmetric KL-divergence reading next to each pair — a secondary measure of how structurally inconsistent the two prices are (a 10pp gap at 50/40 is a different beast than 10pp at 90/80) — but the ARB / WATCH / ALIGNED call is made on the price gap itself.

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.

Common questions

Does the Arb Scanner cover sports like the NBA and World Cup? Yes — the scanner covers 5 sports: NBA, NHL, MLB, NFL, and the 2026 World Cup, matching Kalshi game markets against Polymarket on the same matchup. Sports gaps are scored on the same implied-probability gap as macro markets, and trade routing sends you to Kalshi first. Season gating means a sport only appears when its games are live, so the active list shifts through the year — the World Cup slate, for example, opens in mid-June.

Do I need a paid plan to use the Arb Scanner? The Arb Scanner is a Pro tool at $14.99/mo, which unlocks direct trade links, the Sports tab, and real-time refresh across Kalshi and Polymarket. The free tier still lets you check edge on any single contract through the EV Calculator, but live cross-platform gap detection and one-click trade routing are Pro-only. Annual billing runs $150/yr, which works out to two months free versus paying monthly.

How fresh are the prices the scanner shows? The scanner saves no state — every run pulls live prices, and the sports gap feed refreshes on its own 15-minute cycle. Each page load reflects the current Kalshi and Polymarket order books, not a cached snapshot. Because cross-platform gaps can close in seconds once order flow reacts, re-check both books at the moment of execution rather than trusting a price you loaded minutes earlier.