Best Prediction Market API for 2026

Prediction markets let developers and traders bet on real-world outcomes—elections, Fed decisions, crypto prices, and more. By 2026, these markets are a major data source, with Polymarket alone handling billions in volume. If you’re building trading bots, dashboards, forecasting tools, or news products, you need a reliable prediction market API feed.

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The challenge: every API differs. Some use on-chain WebSockets, others offer CFTC-regulated REST endpoints, and a few are built for play money prototyping. Picking the wrong API can waste weeks due to mismatched auth flows, rate limits, or unsupported data formats.

This guide compares the top prediction market APIs for 2026, explains their strengths, and shows how to evaluate and test them with Apidog. Official docs are spread across Polymarket, Kalshi, and Manifold Markets. If you’re working on-chain, see our guide to the best crypto wallet API for Polymarket and Augur integrations.

TL;DR

• Polymarket: Deepest liquidity, on-chain CLOB and Gamma APIs. Ideal for high-volume trading and election data.
• Kalshi: Only CFTC-regulated US event exchange. REST and WebSocket APIs; requires KYC for trading.
• Manifold Markets: Play-money, clean REST API. Great for prototyping, research, and learning.
• Augur v2: Runs on Ethereum via subgraph. Niche, low volume, fully decentralized.
• PredictIt: Public read-only feed, strict rate limits. Use for data, not trading.
• Metaculus: REST API for research and aggregated forecasts. No trading.

What to Look for in a Prediction Market API

Before integrating, evaluate these 7 criteria:

1. Market coverage: Does it cover politics, sports, crypto, and more, or just one category? (Polymarket/Kalshi = broad; PredictIt = US politics only.)
2. Liquidity & volume data: Need endpoints for 24h volume, open interest, resolver status.
3. Real-time feeds: REST polling is limited. Prefer APIs with WebSocket support for live data.
4. Historical data: Backtesting requires long-term, minute/tick-level data. Some APIs limit free access to 30 days.
5. Regulated status: US users need CFTC-regulated APIs (Kalshi) or must handle IP restrictions.
6. Auth model: Trading often requires API keys, wallet signatures, or KYC.
7. Rate limits & SDKs: Know the per-IP or per-key limits. (Polymarket: ~50 req/sec; Kalshi: tiered; Manifold: relaxed.)

Comparison Table

Provider	Type	API style	Trading auth	Best for
Polymarket	Decentralized, on-chain (Polygon)	REST (CLOB, Gamma) + WebSocket	EIP-712 wallet signature	High-volume crypto-native trading and election data
Kalshi	CFTC-regulated US exchange	REST + WebSocket	Email/password + API key, KYC	US-compliant event contracts and regulated products
Manifold Markets	Play-money social market	REST (clean JSON)	API key	Prototyping, research, teaching
Augur v2	Decentralized (Ethereum)	The Graph subgraph + contracts	Wallet signature	Fully decentralized, censorship-resistant markets
PredictIt	Regulated US political market	Public JSON feed (read)	No public trading API	Historical US political sentiment data
Metaculus	Forecasting research platform	REST	Token auth	Aggregated expert forecasts, research datasets

Top Prediction Market API Providers

Polymarket (CLOB and Gamma)

Polymarket is the largest decentralized prediction market (Polygon, USDC). It exposes two APIs:

• CLOB API: Orderbook data, trades, order placement.
• Gamma API: Market metadata, event grouping, category browsing.
• WebSocket: Real-time trades and orderbook updates.

Read endpoints are open. Trading requires EIP-712 signatures from a Polygon wallet. Use the Polymarket SDK to generate signatures, and integrate wallet providers like Privy or MetaMask. See our guides on using the Privy API and MetaMask API for implementation.

Best for: High-volume trading, election markets, on-chain teams.

Example: Get Polymarket markets

curl https://clob.polymarket.com/api/markets

Kalshi

Kalshi is a CFTC-regulated US event exchange. It covers macro (CPI, Fed), weather, politics, sports, and entertainment. The API uses REST and WebSocket; docs here.

Trading requires a verified account (KYC) and API keys. Orderbooks and trades need authentication. The API enforces per-tier rate limits and token refresh flows, so handle token caching and rotation.

Best for: US-compliant trading, macro and sports automation.

Example: Get Kalshi markets

curl -H "Authorization: Bearer {TOKEN}" https://trading-api.kalshi.com/trade-api/v2/markets

Manifold Markets

Manifold uses “mana” (play money), so you can prototype with zero risk. The REST API (docs) is straightforward. Read markets, comments, and profiles without auth. Betting requires an API key; creating a test account is simple.

Best for: Prototyping, tutorials, student projects, hackathons.

Example: Get Manifold markets

curl https://api.manifold.markets/v0/markets

Augur v2

Augur is a decentralized Ethereum prediction market (REP token). Most access is via The Graph subgraph (GraphQL). For trading, interact with smart contracts directly.

Developer notes: Documentation is sparse, markets are slow, and Ethereum gas costs apply. Integrate with an Ethereum node provider; see our Alchemy API guide.

Best for: Decentralized apps, censorship resistance, research.

Example: Query Augur with GraphQL

{
  markets(first: 5) {
    id
    description
    outcomes {
      price
    }
  }
}

PredictIt

PredictIt is a regulated US political market. No trading API, but a public JSON feed is available at:

https://www.predictit.org/api/marketdata/all/

Usage: Consume as a read-only data source. Rate limits are strict; implement caching and exponential backoff on 429 errors.

Best for: US political price data, sentiment research.

Example: Fetch PredictIt data

curl https://www.predictit.org/api/marketdata/all/

Metaculus

Metaculus is a forecasting platform—no trading, but high-quality aggregated predictions. The REST API (docs) returns questions, predictions, and history using token auth.

Best for: Research, dashboards, academic datasets.

Example: Get Metaculus questions

curl https://www.metaculus.com/api2/questions/

How to Choose

• Compliance: For US retail and real money, pick Kalshi. For crypto-native with wallet auth, pick Polymarket.
• Coverage: Elections—Polymarket (liquidity), Kalshi (wider contract list). Crypto—Polymarket. Play money/education—Manifold.
• Stack fit: On-chain teams: Polymarket, Augur. REST-first teams: Kalshi.
• Backtesting/data: PredictIt (US politics), Metaculus (aggregated forecasts).

Testing Prediction Market APIs with Apidog

Each API uses different auth and flows. Kalshi rotates login tokens, Polymarket requires EIP-712 signatures, Manifold uses API keys, Metaculus uses token auth. Managing these in Postman is messy.

Apidog provides a unified workspace for:

• Importing OpenAPI specs
• Attaching environment-specific auth profiles
• Chaining requests into test scenarios
• Mocking API responses
• Running pre-request flows (e.g., Kalshi login)
• Diffing payloads to catch schema changes

For multi-venue dashboards or bots, Apidog can save hours over juggling curl, Postman, and scripts. Download Apidog and import the Polymarket/Kalshi OpenAPI spec to get started.

FAQ

Which prediction market has the most liquidity in 2026?

Polymarket leads, especially for elections and macro events. Kalshi is second, growing on US-regulated contracts.

Can I trade Polymarket from the US?

No—Polymarket blocks US IPs for trading, per CFTC settlement. Market data is still accessible. Use Kalshi for US-compliant trading.

Do I need a crypto wallet for Polymarket’s API?

Yes, for trading. Read endpoints are public, but placing/canceling orders needs EIP-712 signatures from a Polygon wallet. See our MetaMask API guide.

Is there a free prediction market API for learning?

Manifold Markets is fully free (play money). Metaculus is also free for read access.

Kalshi vs. Polymarket for developers?

Kalshi: REST/WebSocket, email auth, CFTC-compliant.

Polymarket: On-chain, wallet signatures, higher liquidity, no US retail trading. Choose based on jurisdiction and settlement needs.

How do I avoid rate limits while backtesting?

Cache snapshots locally, respect 429s with exponential backoff, and batch WebSocket subscriptions if possible. For more, see API testing without Postman in 2026.