Prediction-market & sportsbook spread scanner
ArbTrader checks every open Kalshi, Polymarket and Polymarket US event for bundles that pay out more than they cost, priced against the live order book, after each platform’s fees, and shows you the exact legs, prices, size and links. It all runs at arbtrader.co: nothing to install, and your P&L is read in your own browser with keys that never leave it. See what has to be true first →
Base is free, no card. Pro from $19.99/month at launch pricing. Runs in your browser, no download, no setup. Your exchange keys stay in your browser; we never receive them.
How it works
Start your trial and log in at arbtrader.co. There is nothing to download, and the scanner is already running, the feed is there the moment you arrive.
Add a Kalshi API key and your Polymarket wallet address to see your own profit & loss; on Max, add a Kalshi or Polymarket US key with trading permission for order tickets. The private key is imported into your browser’s key store, where page code can sign with it but can’t read it back out, and it never reaches our servers.
Every opportunity shows the exact contracts, prices, size resting at those prices, fees taken out, and a direct link to each leg, so you can check it yourself before anything happens.
Pro: click through and place each leg yourself. Max: open an order ticket for the Kalshi or Polymarket US legs, set the size, confirm, and each leg is signed in your browser and sent as a fill-or-kill limit order, one at a time. International Polymarket legs and sportsbook bets are always placed by you; Polymarket.com doesn’t accept orders from other websites.
What it detects
One event where exactly one listed outcome must win, a Polymarket winner-take-all event, Kalshi brackets that cover every possible result, or on Polymarket US a 3-way soccer result or a championship with every team listed. Buy YES on every outcome for under $1, or NO on every outcome for under the payout, and the payout is fixed, as long as every leg fills at those prices. Events where an unlisted result could win are skipped. On every plan, Base included.
Two brackets on the same number in one event, where one range contains the other: “4.00% or above” happens whenever “4.25% or above” does. Buy YES on the wider and NO on the narrower for under $1 and the dollar is fixed, whatever the number turns out to be. Two legs instead of five, and a single bracket carries far more resting size than a whole ladder. On every plan, Base included.
A Kalshi market and a Polymarket market that look like the same real-world event. Search both platforms on your dashboard (the market list refreshes every minute), read both sets of rules, and confirm the pair yourself; only pairs you confirm are priced, and they’re re-priced every minute. Max.
One game, two sportsbooks: the cheapest price on one team from one book plus the cheapest price on the other team from a different book costs less than $1 combined. Same game, same clock, just priced differently by different bookmakers. Max. ArbTrader never places a bet.
Why the list is short
Plenty of screens will show you two prices that don’t match. Most of those aren’t trades. Here is everything that has to hold first.
Exactly one listed outcome must win, or one bracket’s range must contain another’s. Events where an unlisted result could win are skipped even when the prices look free. The scanner sets aside thousands of events a sweep for exactly that reason.
Every leg is priced at the live best ask and the quantity actually offered there, then each platform’s own published fee formula comes off. A spread that clears before fees and not after never reaches the table. That is why the number you see is smaller than the ones screenshotted on social media.
One tap sends every Kalshi and Polymarket US leg as a fill-or-kill limit order, up to 40 legs, thinnest book first, signed in your browser with keys that never reach our servers. Nothing is sent until you confirm the ticket. A read-only screen stops at the row. Max.
This is not the fastest scanner and doesn’t claim to be: the feed re-prices about once a minute, and dedicated bots react in milliseconds. What survives here is what they skip, on quieter venues, at sizes not worth their time, or with money tied up for weeks.
How this is different
Most arbitrage tools are screens: they compare prices, flag the difference and hand you a link. That is genuinely useful, and it stops three steps short of a position. Here is where the two part company.
It does one thing
ArbTrader only looks for arbitrage. There is no model here, no fair-value estimate, no rating, no pick, and no opinion about which way a market is heading. Every number on this site comes from two places: a structure that can be proved, and the live order book behind it.
That is deliberately a narrower product than a general betting tool, and the narrowness is the feature. A tool that ranks bets by expected value is only as good as the model behind the estimate, and you inherit whoever built it. Here there is nothing to inherit. You never have to trust our view of an event, because we do not have one: either exactly one listed outcome must win and the legs cost less than the payout after fees, or there is no row.
Two prices don’t match, so it shows you both.
Checks whether both prices can be wrong at once. It proves that exactly one listed outcome must win, or that one bracket’s range contains another’s, before the row exists. When it can’t prove it, the event is dropped.
Quotes the headline price at the top of the book.
Quotes the size actually resting at that price, on every leg, and takes each platform’s own published fee formula off before calling anything a spread. A gap that only exists before fees never appears.
Ends at a link. You retype the trade somewhere else, leg by leg, while the price moves.
Ends at a confirmed order. One tap sends every Kalshi and Polymarket US leg as a fill-or-kill limit order, up to 40 legs, thinnest book first, signed in your browser. Max.
Where a screen wins: raw speed, and the number of sportsbooks it watches. A dedicated odds screen re-prices in about a second and follows a hundred books; this re-prices in about a minute and follows three exchanges. If you are hunting second-by-second sportsbook arbitrage, that screen is the better buy. If you want prediction-market spreads that are proven before you see them and placeable when you do, that is this.
Pricing
Base is free and shows you every spread the moment it appears. Pro adds the legs, prices and links you need to take one, and your P&L. Max adds alerts, the pairs and sportsbook lines you can only get by combining platforms, and an order ticket for Kalshi and Polymarket US.
Base
freeFree for as long as you want it. No trial to run out.
See every qualifying spread the moment the scanner finds it.
Pro
3-day free trialLaunch price for subscriptions started by Dec 31, 2026. New subscriptions after that are $30/mo.
Everything in Base, unlocked: the legs you need to take a spread, and your P&L.
Max
recommendedLaunch price for subscriptions started by Dec 31, 2026. New subscriptions after that are $45/mo. 3-day free trial.
Everything in Pro, plus alerts, more kinds of spread, and one-tap Kalshi and Polymarket US tickets.
How billing works: card required at checkout; you won’t be charged during the 3-day trial. If you don’t cancel before it ends, your plan renews monthly at the price shown, plus any sales tax (shown at checkout before you pay), until you cancel. No setup fees and no other ArbTrader charges, exchange trading fees are charged by the exchanges, not us. Switch plans or cancel anytime from your account page; see the refund policy. Refer a friend: they get 50% off their first paid month, and you get 50% off a month when they subscribe. Your exchange keys stay in your browser and your funds stay on the exchange; neither ever touches our servers.
Before you pay for this
Nothing on this page is financial, legal, or betting advice. Past spread detection does not guarantee future opportunities, and trading and betting both involve risk of loss, including total loss of amounts wagered or traded.
FAQ
A spread scanner for prediction markets and sportsbooks that runs on the web. Log in at arbtrader.co and your dashboard checks every open Kalshi, Polymarket and Polymarket US event for bundles that pay more than they cost after fees, and shows the legs, prices, size and links. Connect your accounts and it also draws your profit & loss, computed in your browser, from your own trade history. Pro adds alerts, Kalshi ↔ Polymarket pairs you confirm, sportsbook moneylines, and Kalshi and Polymarket US order tickets you confirm.
All three run the same one-winner bundle scanner across every open Kalshi, Polymarket and Polymarket US event. Base is free and shows you each spread as it appears, with its return and how long it has left, but not the legs, prices, sizes or links; you can watch the scanner work, you just can’t act on it. Pro ($19.99/month launch price, $30 after Dec 31, 2026) unlocks all of that plus your P&L, and you place the trades yourself. Max ($24.99/month launch price, $45 after Dec 31, 2026) adds email and Discord alerts, Kalshi ↔ Polymarket pairs you confirm, sportsbook moneylines, and one-tap Kalshi and Polymarket US order tickets. International Polymarket legs and sportsbook bets are placed by you on every plan.
Never on its own. On Base and Pro, no; they report opportunities and Pro links you to each leg, and you place every trade by hand. On Max it can send Kalshi and Polymarket US orders, but only when you open the ticket for a specific opportunity, set the size, let it re-check the live prices, and confirm. There's no auto-trade setting, and each leg goes out as a fill-or-kill limit order at the price you approved. International Polymarket blocks orders placed from other websites, so those legs are always yours to place; sportsbook bets are never placed by ArbTrader either; sportsbooks don't offer a betting API, and most prohibit automated wagering.
You do. Your Kalshi private key (and, for Max tickets, your Polymarket US secret) is imported into your browser’s own key store as a non-extractable key: the dashboard can ask the browser to sign a request with it, but neither the page nor we can read the key back out, and it is never uploaded. Each request is signed in your browser and passed through arbtrader.co only because the exchanges’ APIs don’t accept calls from web pages; we forward the signed request and the exchange’s answer, and never see the key. International Polymarket needs only your public wallet address. We never hold your funds on any platform.
Just an ArbTrader account. The live feed works the moment you log in; it uses public market data, not your accounts. A Kalshi API key and your Polymarket wallet address are optional and only power your P&L; on Max, a Kalshi or Polymarket US key with trading permission powers order tickets. Discord alerts need a webhook URL from a server you control. You add all of these on the Connections tab of your dashboard, and you can remove them with one click. Want to look around first? Try the live demo.
The dashboard re-prices every listed spread about once a minute and sweeps all open events in rolling passes, so it can lag the market. Order tickets re-read the live order book the moment before you confirm, and refuse the ticket if the price moved or the size isn't there. Sportsbook odds refresh on a slower, credit-budgeted schedule. Real spreads are rare and close fast; a human confirmation is part of every order by design, and nothing guarantees a fill at the price you saw.
Not on raw speed, and we don’t claim to. Dedicated bots stream every order book and react in milliseconds; ArbTrader re-prices about once a minute and a person confirms every order. Where it earns its keep is the spreads bots tend to skip: cross-platform pairs that need a human to read both sets of rules, newer and quieter venues like Polymarket US, small sizes that aren’t worth a bot’s time, and spreads that tie money up for weeks. It also saves you hours of checking every event by hand.
No. ArbTrader is software that surfaces pricing information across platforms and, on Pro, sends orders you've reviewed and confirmed. Whether to trade, and how much, is always your decision and your risk.
Yes, anytime, including during the trial; you won't be charged unless you're still subscribed when it ends. Switch between Pro and Max from Manage billing on your account page, or drop back to Base for free. It's a monthly subscription with no lock-in.