Polymarket × Kalshi Arbitrage Scanner — Matched Markets & Fee-Adjusted Edge

Find the same prediction market on Polymarket and Kalshi, compare live YES/NO ask prices, and get the fee-adjusted, risk-free arbitrage edge for every matched pair — in one run, from two public APIs, with no login and no API keys.

Built for prediction market traders, arbitrageurs and researchers who are tired of eyeballing two browser tabs: the scanner matches markets by entity (names, numeric strikes, dates), blocks false pairs (negation, above/below direction, mismatched strikes), and computes the exact cost of buying YES on one platform and NO on the other — including Kalshi's 7% trading fee.

Why this scanner instead of eyeballing?

• Entity-exact matching, not keyword soup. "Fed rate be 1.75%" will never be paired with "Fed rate above 2.75%". Numeric strikes must agree, end dates must be close, negations and directions must match.
• Fee-adjusted edge. A 1.5% gross gap that dies after Kalshi fees is not an arb. netEdgePct already subtracts the fee.
• Verified arbs first. Rows are sorted with high-confidence, net-positive arbs on top (isArb: true). Edges above 15% are flagged suspiciousEdge — cross-platform gaps that big are almost always a market mismatch, so we never charge you optimism.
• Whole-market coverage. Scans ~2,000 highest-volume Polymarket binary markets and every open Kalshi market (tens of thousands) per run.

Output fields

Field	Description
matchScore / confidence	Match similarity (0–1) and high/medium tier
question, polyEventTitle, polyUrl	Polymarket market
polyYesAsk, polyNoAsk, polyVolumeUsd, polyEndDate	Polymarket prices & volume
kalshiTicker, kalshiQuestion, kalshiUrl	Kalshi market
kalshiYesAsk, kalshiNoAsk, kalshiCloseTime	Kalshi prices
direction	Best arb legs, e.g. YES@Polymarket + NO@Kalshi
totalCostUsd, kalshiFeeUsd	Combined cost of both legs + fee
grossEdgePct, netEdgePct	Edge before / after Kalshi fees
isArb	true = verified net-positive arb (high confidence, sane edge)
suspiciousEdge	true = edge >15%, verify the pair manually
scannedAt	UTC timestamp of the scan

Pricing

$0.04 per run + $2.00 per 1,000 matched pairs. A full scan typically returns 300–600 pairs (≈ $0.6–1.2 per full price-gap table). Set minNetEdgePct: 0 to receive only net-positive arbs — then a run costs $0.04 plus a fraction of a cent per actionable opportunity.

Run it on a schedule (recommended)

Arbs live for minutes to hours. In Apify Console: Actors → this actor → Schedules → Create new, pick every 15–60 minutes, set input { "minNetEdgePct": 0 }, and add an email/Slack/webhook integration that fires when the dataset is non-empty. You'll only pay for rows that are actually actionable.

Use with AI agents & MCP

This actor works out of the box with the Apify MCP server — plug it into Claude, ChatGPT, LangGraph or any agent framework and ask things like "scan for prediction-market arbitrage above 1% and summarize the top 5". The output schema is stable and machine-readable, so agents can chain it into alerting, sizing or execution research workflows.

Related actors

• Kalshi Weather Markets Scraper — live Kalshi weather market odds by city.
• Whop New Launches Monitor — catch every new Whop product the hour it launches.
• Ad Budget Signals — which advertisers are scaling spend right now.
• Polymarket Top Traders Scraper — Whale Positions & Copy Feed — see what the most profitable Polymarket whales are holding right now.

Legality & fair use

Both data sources are public, unauthenticated JSON APIs (Polymarket Gamma API, Kalshi trade API v2). The scanner uses polite pacing, no proxies and no credentials. This actor provides market data, not financial advice — always verify prices on-platform before trading.