ArbScout
Finds the same contract priced on Kalshi and Polymarket US, and tells you which side pays more after fees — or that neither does.
Overview
A research tool for prediction-market traders. Every hour ArbScout reads up to 15,000 open markets per venue on Kalshi and Polymarket US, matches the ones that ask the same question on their resolution rules, walks both order books to the size you care about, subtracts each venue's own fees, and ranks what is left by annualized return — or says there is nothing worth acting on. It places no trades and holds no money: it is information only, not investment or financial advice, and it makes no promise of profit.
The problem
Two exchanges can list the same question at different prices, but a quoted gap is not an edge. Fees are a curve rather than a percentage, the top of the book is good for one contract, and two markets that sound identical can settle differently — in which case both legs lose at once.
The approach
A scheduled Lambda rescans both venues every hour. Candidate pairs are matched on normalized titles and then compared on their resolution rules, and a deterministic comparer grades each pair A to D on how confidently the two are the same contract; an optional LLM pass can only ever lower a grade, never raise it. Prices come from walking each order book to the chosen size and applying each venue's fee formula, results are ranked by annualized return, and every number shows the age of the order book it came from. Built on Next.js 16 and React 19 with Drizzle on Aurora Serverless v2, Auth.js v5 magic-link sign-in over SES, Stripe subscriptions, and SST 4.
Highlights
- A scheduled Lambda rescans both venues every hour
- Markets matched on title, then on resolution rules, with every rule difference written out and an A–D confidence grade
- Order books walked to the requested size and each venue's own fee formula applied, so every edge is net of fees
- Price lookup: which venue pays more for a position you already want to take, useful even on days with no arbitrage
- No trading permissions and no custody of funds, by design
Pricing
$10 a month, or $25 every 3 months. No free tier.
As listed on the ArbScout site on 2026-09-25. The price shown at checkout on the product's own site is the one that applies.
Policies
Each product's own terms govern its use and any purchase. All Idea Engine LLC policies
Tech stack
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