Prediction-market spread scanner

The spread scanner for prediction markets.

ArbTrader watches Kalshi and Polymarket around the clock for same-market and cross-platform spreads, and lays out the exact legs, prices, and sizes so you can act on them.

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Self-hosted. Runs on your machine, with your own API keys — never ours.

Live opportunity feed Example data
Fed holds rates at March meeting
Same-market
+3.1%spread
City Council Bill 118 passes by Jun 30
Cross-platform · confirmed
+5.3%spread
Named storm makes landfall in FL before Oct 1
Same-market
+1.8%spread
Illustration of the dashboard feed — not real-time market data.

How it works

From scan to trade in four steps.

01

Install & connect

Run ArbTrader on your own machine and add your Kalshi and Polymarket API keys. They stay local — we never see them.

02

Watch the feed

Same-market and cross-platform spreads populate live on your dashboard as they're detected.

03

Review the legs

Every opportunity shows the exact contracts, prices, and sizes before anything is confirmed.

04

Take the trade

One click submits both legs together, at the prices you reviewed.

What it detects

Two kinds of spread, two levels of trust.

Same-market

High confidence

One platform, one market: every outcome summed costs less than $1. This is arbitrage by construction — same contract, same resolution rules, no judgment call involved.

Cross-platform

Confidence depends on you

A Kalshi market and a Polymarket market that look like the same real-world event. ArbTrader surfaces title-similarity matches for you to inspect and confirm before they're tradable.

Before you pay for this

What you're actually buying

  • This is beta software that can place real trades with real money. The order-placement paths for both platforms are built and code-reviewed but have not been exercised against live trading accounts.
  • Kalshi has a free demo environment — use it first. Polymarket has no equivalent paper-trading network, so your first live order there is a real one. Start small.
  • The two legs of a trade are not placed atomically. If one fills and the other fails — a stale price, a network hiccup — you're left holding a real, unhedged position. ArbTrader flags this in the trade log; it does not auto-unwind it for you.
  • Displayed spreads subtract a rough, constant fee estimate, not each platform's live, current fee schedule. Check real fees before sizing up.
  • Capital sits locked up until a market resolves. Judge an opportunity by its annualized return, not the raw spread shown — 3% on a market that resolves in four months is not 3% overnight.
  • Legality and tax treatment of prediction-market trading vary by state and country and are still actively evolving for both platforms. Confirm you're eligible to trade from your location before connecting real accounts.

Nothing on this page is financial or legal advice. Past spread detection does not guarantee future opportunities, and trading involves risk of loss — including total loss of amounts traded.

Pricing

One plan. Cancel anytime.

ArbTrader license

7-day free trial
$30/month after
  • Full ArbTrader source + setup docs
  • Kalshi and Polymarket integrations, both included
  • Same-market and cross-platform detection
  • Updates for as long as you're subscribed
  • Email support for setup and configuration
Start your free trial

7 days free, then $30/month, billed via Stripe. Cancel anytime. Runs entirely on your own machine — your API keys and funds never touch our servers.

FAQ

Questions worth asking before you subscribe.

What is ArbTrader?

A spread scanner for prediction markets. It watches Kalshi and Polymarket for same-market and cross-platform spreads and shows you the exact trade — the legs, the prices, the sizes — as it finds them.

Do you ever hold my funds or API keys?

No. ArbTrader is self-hosted: you run it on your own computer or server, and your Kalshi API key and Polymarket wallet key stay there. We never receive, store, or have access to either.

What accounts do I need?

A Kalshi account to trade same-market opportunities. Both a Kalshi and a Polymarket account, funded on each, to take cross-platform trades. You can also run it against bundled sample data with no accounts at all, just to see how it works.

Is this financial advice?

No. ArbTrader is software that surfaces pricing information across two platforms. What you do with that information — if anything — is your decision and your risk.

Can I cancel?

Yes, anytime, including during the trial — you won't be charged unless you're still subscribed when it ends. It's a monthly license with no lock-in after that.