Prediction Markets APIs
Prediction market APIs expose prices and order books for event contracts rather than sportsbook lines. Polymarket and Kalshi are both free to read, with Polymarket adding WebSocket streams and Kalshi providing trades and candlesticks. Manifold Markets runs on play money, and VoxOdds combines Polymarket and Kalshi odds with forecast scoring and arbitrage detection. Free Sports APIs →
| API | Pricing | Auth | Format | Free tier | Status |
|---|---|---|---|---|---|
KalshiPrices, order books, trades and candlesticks for event contracts on politics, economics, weather and sports. Sports › Betting Odds | Free | None | JSON | — | Live |
Manifold MarketsQuestions, probabilities, bets and comments from a play-money prediction market on news, tech and politics. Sports › Betting Odds | Free | None | JSON | 10k+/day | Live |
PolymarketReal-time prediction-market data: event odds, prices and order books, plus WebSocket streams. Finance & Commerce › Stock Market | Free | None | JSON | Unlimited | Live |
VoxOddsPrediction-market odds from Polymarket and Kalshi, with audited forecast scores and arbitrage detection. Sports › Betting Odds | Free | None | JSON | 10k+/day | Live |
KalshiFreeLive
Prices, order books, trades and candlesticks for event contracts on politics, economics, weather and sports.
None · JSON
—
OpenAPI spec
Manifold MarketsFreeLive
Questions, probabilities, bets and comments from a play-money prediction market on news, tech and politics.
None · JSON
10k+/day
no machine-readable spec
PolymarketFreeLive
Real-time prediction-market data: event odds, prices and order books, plus WebSocket streams.
None · JSON
Unlimited
llms.txt
VoxOddsFreeLive
Prediction-market odds from Polymarket and Kalshi, with audited forecast scores and arbitrage detection.
None · JSON
10k+/day
MCP server · llms.txt
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Choosing a Prediction Markets API
Is there a free Prediction Markets API?
Yes. Polymarket, Kalshi, Manifold Markets and VoxOdds are free to use. See all free Sports APIs.
Which Prediction Markets APIs work without an API key?
Polymarket, Kalshi, Manifold Markets and VoxOdds need no key or sign-up, so you can try them with a plain request.
Can I call a Prediction Markets API from front-end JavaScript?
Polymarket and Manifold Markets allow cross-origin requests and need no key, so they work straight from the browser. For the others, call them from your server so your key stays private.
Can I use Prediction Markets APIs in a commercial project?
Manifold Markets and VoxOdds restrict it, for example to non-commercial or attributed use, so read the terms first.
Which Prediction Markets APIs work with AI agents?
VoxOdds has an MCP server, so an AI agent can call it directly. Kalshi publishes an OpenAPI spec for generating clients and tools.
Broader: Betting Odds APIs · Sports APIs
More in Betting Odds: Player Props APIs