Official venue APIs
Official prediction market APIs: Kalshi, Polymarket and every other venue
First-party APIs from Kalshi, Polymarket, Predict.fun and other venues: endpoints, auth schemes, rate limits and sandboxes, verified against live docs.
Checked September 8, 2026 · every price read off the live site
Every official venue apis API
14 reviewed · alphabetical-
Kairos Cross-venue trading terminal: Kalshi, Polymarket and Predict.fun in one order book, with sub-second data and advanced order types.
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IBKR ForecastEx Event contracts through the full Interactive Brokers stack (TWS API and Web API). Buy-only contracts with netted exits; the heaviest setup of any venue.
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Kalshi Trading API REST, WebSocket and FIX for event contracts and perps. RSA-PSS auth, real demo environment, token-bucket rate tiers from 200 to 10,000 reads/sec.
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Limitless API Prediction markets on Base: REST and WebSocket, wallet-signature auth with EIP-712 orders, CLOB plus AMM markets, TypeScript SDK.
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Manifold API Play-money forecasting with the friendliest API: plain key auth, 500 req/min, WebSocket, and the entire platform is open source.
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Metaculus API Forecast probabilities rather than tradable markets. Token auth, full schema published. Great for research pipelines.
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Myriad API Agents and market makers who want one REST and WebSocket surface over both AMM and order-book markets on BNB Smart Chain, with a staging environment.
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Novig API P2P sports exchange: REST, WebSocket and GraphQL with OAuth 2.0 and a downloadable OpenAPI 3.1 spec. Rate limits unpublished.
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Opinion Open API Reading and trading Opinion's BNB Chain prediction markets from Python with a self-serve key.
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Polymarket CLOB + Gamma The largest global book: CLOB for trading, Gamma for metadata, Data API, WebSocket feeds. EIP-712 + HMAC auth. US and UK IPs blocked from ordering; no sandbox.
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Polymarket US API A separate CFTC-regulated exchange with a completely different API: ~23 REST endpoints, two WebSocket feeds, Ed25519 key signing, KYC-verified US users.
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Predict.fun API Orderbook markets on BNB Chain. API-key auth, a real testnet needing no key, 240 req/min default, official TypeScript and Python SDKs.
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PredictIt (older API) Read-only US politics odds, no auth, roughly one request per minute. Fine as a free ticker, nothing more.
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ProphetX API Regulated P2P sports exchange: four purpose-built APIs, limit orders, real-time odds, 99.5%+ uptime SLO. You must be located in an operating state.
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SX Bet API Sports market makers and bot builders who want an open order book, a full testnet (Toronto) and per-endpoint rate limits in the thousands per minute.
| API | Venues | Pricing | Type |
|---|---|---|---|
| IBKR ForecastEx | ForecastEx | Standard Interactive Brokers account; no separate API fee is listed. | API |
| Kalshi Trading API | Kalshi | Free. | API |
| Limitless API | Limitless | Free. | API |
| Manifold API | Manifold | Free. | API |
| Metaculus API | Metaculus | Free with an account. | API |
| Myriad API | Myriad | Free. | API |
| Novig API | Novig | Free. | API |
| Opinion Open API | Opinion | Free. | API |
| Polymarket CLOB + Gamma | Polymarket | Free. | API |
| Polymarket US API | Polymarket US | Free API access after identity verification. | API |
| Predict.fun API | Predict.fun | Free. | API |
| PredictIt (older API) | PredictIt | Free. | API |
| ProphetX API | ProphetX | Not stated. | API |
| SX Bet API | SX Bet | Free. | API |
How these APIs work
Official venue APIs are the first-party interfaces each exchange or forecasting site publishes for its own markets. They are the only path to placing orders, reading your fills or streaming an order book with no intermediary, and their documentation is the source every aggregator and SDK ultimately copies.
They differ more than their landing pages suggest. Auth ranges from a single header (Manifold) to RSA-PSS request signing (Kalshi), EIP-712 wallet signatures plus HMAC (Polymarket, Limitless) and Ed25519 keys behind KYC (Polymarket US). Some publish exact rate tables (Kalshi, Novig, SX Bet, Polymarket US); others say limits exist and stop there (ProphetX, Limitless).
Test environments are the second big split. Kalshi, Predict.fun, SX Bet, Novig, ProphetX and Myriad document a demo, testnet, QA or staging host. Polymarket, Polymarket US, Limitless and Opinion document production only, so the first order is live.
How to choose
- Start from jurisdiction and money: Kalshi, Polymarket US, ProphetX, Novig and ForecastEx are US-regulated and fiat; Polymarket, Limitless, Predict.fun, Opinion, Myriad and SX Bet settle in stablecoins on chain; Manifold and Metaculus have no money at all.
- Check the published rate limit against your polling plan before you write code. 20 requests per second (Polymarket US), 15 per second (Opinion) and 240 per minute (Predict.fun) rule out naive scanners; use the WebSocket feeds instead.
- Prefer a venue with a demo or testnet if you have never traded programmatically. Kalshi's demo with mock funds and SX Bet's Toronto testnet are the most complete.
- Read the fee page as a taker and as a maker separately. Nearly every venue here charges takers only, and maker rebates on Polymarket, Polymarket US and Novig can turn quoting into income.
- Weigh SDK support in your language. Kalshi, Polymarket, Polymarket US, Predict.fun and Limitless ship official Python and TypeScript clients; Opinion is Python-only, SX Bet and Novig are raw REST.
Questions about official venue apis APIs
Which prediction market has the best API?
For a regulated US venue, Kalshi: REST, WebSocket and FIX, a demo environment, published rate tiers and official SDKs. For global depth, Polymarket's CLOB with the unified TypeScript and Python SDKs.
Which prediction market APIs are free?
All of the ones listed here charge nothing for API access. You pay venue trading fees on fills, and some (Polymarket US, ProphetX, Novig) require identity checks or an application before keys are issued.
Which prediction market APIs have a sandbox or testnet?
Kalshi (demo.kalshi.co with mock funds), Predict.fun (keyless testnet), SX Bet (Toronto testnet), Novig (QA environment), ProphetX (funded sandbox) and Myriad (staging host). Polymarket, Polymarket US, Limitless and Opinion document production only.
Official APIs for building. One book for trading.
Rather trade the spread than build the plumbing? The free Kairos terminal gives you Kalshi, Polymarket and Predict.fun in one order book.