Prediction market platforms that offer public APIs for algorithmic and automated trading.
API access transforms prediction markets from a manual browsing experience into a programmable trading platform. With a good API, you can build bots that monitor prices across hundreds of markets, execute trades in milliseconds when conditions are met, analyze historical data at scale, and manage a portfolio algorithmically. For serious traders, API quality is often the deciding factor when choosing a platform.
Not all APIs are created equal. The most important factors are documentation quality, rate limits, endpoint coverage, and real-time data support. A well-documented API with clear examples saves hours of trial and error. Generous rate limits let you poll prices frequently without getting throttled. Full endpoint coverage means you can do everything through the API that you can do on the website — place orders, check balances, view market details, and manage positions.
Platforms that offer WebSocket connections push price updates instantly, rather than requiring you to poll a REST endpoint repeatedly. This matters when strategies depend on reacting to price movements within seconds.
Kalshi offers one of the most complete prediction market APIs available. Its REST API covers market data, order placement, portfolio management, and account information. Kalshi also provides WebSocket streams for real-time price and order book updates. The documentation is thorough, with code examples and clear rate limit guidelines. For algorithmic traders focused on regulated US markets, Kalshi's API is the gold standard.
Polymarket exposes its markets through a combination of REST endpoints and on-chain data. Because trades settle on the Polygon blockchain, you can interact directly with smart contracts for order placement — giving you the lowest possible latency and no dependence on a centralized API server. Polymarket also provides a CLOB (central limit order book) API for off-chain order matching with on-chain settlement, combining speed with transparency.
Manifold Markets has a particularly developer-friendly API that is open and well-documented. Because Manifold is a play-money platform, there is no financial risk in testing your trading bots, making it an ideal sandbox environment. You can prototype strategies on Manifold and then deploy them on real-money platforms once validated.
Interactive Brokers ForecastTrader integrates prediction market contracts into IBKR's Trader Workstation API, which is one of the most powerful trading APIs in the financial industry. If you already have algorithmic strategies running on IBKR for stocks, options, or futures, adding event contracts requires minimal additional code. The API supports everything from simple market orders to complex conditional logic and portfolio-level risk management.
Begin by reading the API documentation for your chosen platform before writing any code. Test with small orders or on a play-money platform like Manifold Markets. Start with simple strategies — monitoring a set of markets and alerting you when prices cross a threshold — before building fully automated execution systems. And always implement proper error handling and rate limit respect to avoid getting your API access revoked.
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