Prediction Markets API: Polymarket, Kalshi and Manifold Odds, Arbitrage and Kelly Sizing

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Get live prediction market data from Polymarket, Kalshi and Manifold in one normalized JSON format. Pull markets, odds, order books and OHLC price history. Scan for cross-venue arbitrage and dutch-book mispricings. Build a volume-weighted consensus fair value and size your stake with the Kelly criterion. Every run is computed live at request time.

Run it from the Apify Console, call it as an API, schedule it, or plug it into Make, Zapier, n8n, Google Sheets or your own code. Results export as JSON, CSV, Excel or XML.

What can it do?

Operation	What you get	Main inputs
markets	Normalized market list with title, status, volume, liquidity, bid, ask and outcome odds	venue, q, limit
market	One market in full	venue, id
orderbook	Live bids and asks (Manifold returns the AMM probability and pool)	venue, id
odds	Outcomes in probability, decimal and American odds	venue, id
oddsCompare	One topic compared side by side across every venue	q
history	OHLC candles as probabilities from 0 to 1, plus volume	venue, id, interval, lookback, outcome
search	Free-text search merged across the three venues	q, venue, limit
arbitrage	Same question priced differently on two venues, with the guaranteed edge and optional Kalshi fee modeling	q, minEdge, feeAware, limit
arbitrageEvent	Dutch-book check for one multi-outcome event on one venue	venue, eventId, feeAware
arbitrageEvents	The same check across every event found by a search	q, venue, minEdge, feeAware
consensus	Volume-weighted fair value plus a venue disagreement score	q, minSimilarity
kelly	Kelly stake from your probability estimate and the market price	probability, price, bankroll, fraction
venues / health	Supported venues and a liveness check	none

Use venue values polymarket, kalshi or manifold. For operations that compare venues you can pass two or more, comma-separated.

Quick start

Choose an operation, fill only the fields it needs, and click Start.

{ "operation": "markets", "venue": "polymarket", "q": "bitcoin", "limit": 10 }

More examples:

{ "operation": "consensus", "q": "fed rate cut october" }
{ "operation": "arbitrage", "q": "bitcoin", "minEdge": 0.02, "feeAware": true, "limit": 20 }
{ "operation": "history", "venue": "kalshi", "id": "KXHIGHNY-26OCT27-T67", "interval": "1d", "lookback": "30d" }
{ "operation": "kelly", "probability": 0.6, "price": 0.45, "bankroll": 500, "fraction": 0.5 }

Call it from the API

curl -X POST "https://api.apify.com/v2/acts/pintostudio~prediction-markets/run-sync-get-dataset-items" \
  -H "Authorization: Bearer YOUR_APIFY_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{ "operation": "consensus", "q": "fed rate cut october" }'

Output

Every run returns one JSON object. It is saved in the dataset and also in the key-value store as OUTPUT.

{
  "error": false,
  "data": { "...": "operation specific result" },
  "message": "OK"
}

If something goes wrong, error is true, data is null and message explains why.

Who is it for?

• Traders and quants: compare lines across exchanges, find arbitrage and dutch books, backtest on OHLC history.
• Bot and app builders: one schema for three venues, ideal for Telegram bots, dashboards and alerts.
• Journalists and researchers: cite what the market thinks about elections, rates, crypto and sports with a consensus number.
• Data teams: schedule runs and push results to Sheets, a database or a webhook.

FAQ

Is this an official Polymarket, Kalshi or Manifold product? No. It is an independent tool that aggregates and normalizes public market data. It is not affiliated with or endorsed by any of them.

Do I need accounts or API keys for the venues? No.

Is the data real time? Yes. Each run is computed live. Nothing is cached beyond a single run.

Can it place trades? No. It is read-only data and analytics. Trade on the venues themselves.

Is this financial advice? No. Arbitrage, consensus and Kelly outputs are informational. Always verify live prices and liquidity before trading.

Do you also offer a plain REST API? Yes, see the Prediction Markets API on RapidAPI and the open source examples on GitHub.

Support

⚡ Questions, bugs or feature requests? Telegram @pintoflow for the fastest reply.