Prediction market APIs
Prediction market APIs let you read markets, prices and order books and place trades by code. The two main ones are Kalshi's Trade API and Polymarket's Gamma, CLOB and Data APIs, and both serve public market data for free without an API key.
The short answer: for read-only data, call the public endpoints directly. For trading you need credentials: Kalshi uses an API key with signed requests and tiered rate limits; Polymarket uses a wallet signature plus HMAC-signed API credentials. For one interface across venues, the open-source pmxt library wraps both. For history, the free Becker Kalshi dataset has years of Kalshi markets and trades.
Last updated .
Official APIs
| API | Public data without a key | Trading auth | Real-time | Docs |
|---|---|---|---|---|
| Kalshi Trade API | Yes (series, events, markets, order books) | API key + signed requests; tiered token budgets | WebSocket (connection requires auth) | Kalshi: Quick Start, Market Data ↗ · Kalshi: Rate Limits and Tiers ↗ |
| Polymarket Gamma API | Yes (events, markets, metadata) | — | — | Polymarket: API overview ↗ |
| Polymarket CLOB API | Yes (prices, order books) | Wallet signature (L1) + HMAC API credentials (L2) | Public market channel; authenticated user channel | Polymarket: API overview ↗ |
| Polymarket Data API | Yes (positions, activity) | — | — | Polymarket: Wallet activity ↗ |
Rate limits
Kalshi meters authenticated requests in tokens: most requests cost 10, and your tier sets how fast your Read and Write budgets refill (Kalshi: Rate Limits and Tiers ↗). For Polymarket, check its API reference for current limits. Either way, cache public data instead of polling it.
Code: Python SDKs · Kalshi data pages · data & analytics tools
Listed projects compared (9)
From this directory. GitHub stars and update dates as of Oct 23, 2026.
| Project | Platforms | Tools | Difficulty | GitHub stars | Repo updated |
|---|---|---|---|---|---|
| Prediction market analysis framework and dataset | Kalshi & Polymarket | Python, Parquet | intermediate | 3,874 | Oct 9, 2026 |
| poly_data Polymarket data pipeline | Polymarket | Python | intermediate | 2,338 | Sep 8, 2026 |
| PMXT: 'CCXT for prediction markets' | Kalshi & Polymarket | TypeScript | intermediate | 2,170 | Sep 30, 2026 |
| Polymarket MCP server | Polymarket | Python, MCP | beginner | 145 | Jun 6, 2025 |
| Kalshi MCP server | Kalshi | Python, MCP | beginner | 31 | Sep 19, 2026 |
| Real-time tick visualizer | Kalshi & Polymarket | Python, WebSockets | intermediate | 21 | Sep 22, 2025 |
| Polymarket Agent MCP: 48-tool MCP server with preview and live trading | Polymarket | TypeScript, Node.js, MCP, SQLite | intermediate | 16 | Oct 15, 2026 |
| Go client for the Kalshi REST and WebSocket APIs | Kalshi | Go, OpenAPI, AsyncAPI, WebSocket | intermediate | 0 | Oct 17, 2026 |
| Kalshi new-market scanner with Telegram alerts | Kalshi | Python, Telegram | beginner | 0 | Oct 15, 2026 |
FAQ
Is there a free prediction market API?
Yes. Kalshi and Polymarket both serve public market data without an API key. Placing trades incurs each exchange's trading fees.
Is the Polymarket API free?
Public Gamma, CLOB and Data API reads need no credentials. Trading needs a wallet and API credentials, and takers pay fees on some market categories.
What are Kalshi API rate limits?
Kalshi uses token budgets: most requests cost 10 tokens, with separate Read and Write buckets whose refill rate depends on your usage tier.
Is there one API for Kalshi and Polymarket?
Not officially. The open-source pmxt library gives one interface across Polymarket, Kalshi and other venues.
Where can I get historical prediction market data?
The free Becker dataset covers Kalshi markets and trades; poly_data collects Polymarket data. Both are listed above.
Not financial advice. Listing is not an endorsement, and we have not checked any profit claims. Read the code before you give any tool an API key or wallet key.
Related: Kalshi trading bots · Polymarket trading bots · Kalshi vs Polymarket · Python SDKs · All 66 projects
Get the weekly digest
New public Kalshi & Polymarket builds, each with a source. No spam.
Form not loading? Subscribe on beehiiv. Handled by beehiiv; see privacy. Unsubscribe any time.