Prediction markets let traders bet on real-world outcomes: who wins the next election, whether the Fed cuts rates, whether Bitcoin closes above $120k by Friday. In 2026, these markets have grown from a niche research tool into a serious data source, with Polymarket alone clearing billions in election-cycle volume. If you build trading bots, research dashboards, forecasting tools, or news products, you need a prediction market API feed.
The tricky part: the space mixes crypto-native exchanges, regulated US venues, and academic forecasting platforms, each with its own auth model, rate limits, and data shape. One API hands you on-chain orderbooks over WebSocket; another returns CFTC-approved contracts over plain REST; a third is play money for prototyping. Picking the wrong one wastes weeks.
This guide compares the best prediction market API options for 2026, what each covers, and how to test them with Apidog. Official docs sit across Polymarket, Kalshi, and Manifold Markets, so expect to juggle tabs. If you are already building on-chain, our guide on the best crypto wallet API pairs well with Polymarket and Augur work.
TL;DR
- Polymarket offers the deepest liquidity and on-chain settlement via its CLOB and Gamma APIs; best for serious trading volume and election data.
- Kalshi is the only CFTC-regulated US event exchange with a first-party REST and WebSocket API; KYC required for trading.
- Manifold Markets runs on play money with a clean REST API; perfect for prototypes, research, and learning the domain.
- Augur v2 lives on Ethereum with subgraph access; niche, low volume, but fully decentralized.
- PredictIt has a public read-only feed with heavy limits; treat it as a data source, not a trading API.
- Metaculus exposes forecasting questions over REST for research and aggregated probabilities; no trading.
What to look for in a prediction market API
Not every “prediction market” is the same product. Check these seven criteria before you pick one.
- Market coverage and breadth. Does the provider list politics, sports, crypto, macro, and culture, or a single vertical? Polymarket and Kalshi cover broad topics; PredictIt only does US politics.
- Liquidity and volume data. Thin markets produce noisy prices. Look for endpoints that expose 24h volume, open interest, and resolver status.
- Real-time price and orderbook feeds. REST polling breaks down above 1 req/sec. You want WebSocket channels for top-of-book, trades, and market status.
- Historical data. Backtesting needs minute or tick bars going back months. Some APIs only give you the last 30 days free.
- Regulated status. US retail users need a CFTC-regulated venue (Kalshi) or careful IP blocking. Crypto-native venues solve this differently.
- Auth model. Read-only public data is usually open. Trading needs API keys, signed requests, KYC, or wallet signatures depending on the venue.
- Rate limits and SDKs. Polymarket caps CLOB REST reads near 50 req/sec per IP, Kalshi scales limits per tier, Manifold is relaxed for read calls.
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 in the world, running on Polygon with USDC as the base asset. It exposes two surfaces: the CLOB (Central Limit Order Book) API for orderbook data, trades, and order placement, and the Gamma API for market metadata, event grouping, and category browsing. A WebSocket channel streams trades and orderbook updates in real time.
Read endpoints are open; placing orders needs a Polygon wallet signing EIP-712 typed data, which your client builds from the Polymarket SDK. Settlement is on-chain, so you also need gas and a funded USDC balance. To handle signatures from a browser app, pair Polymarket with Privy or MetaMask; our walkthroughs on how to use the Privy API and how to use the MetaMask API cover the signing flow.
Best for: serious trading volume, election markets, and teams comfortable with on-chain mechanics.
Kalshi
Kalshi is the only CFTC-regulated event contract exchange operating in the US. It lists contracts across macro data (CPI, Fed decisions), weather, politics, sports, and entertainment. The API is REST plus WebSocket, and the Kalshi docs are clean and versioned.
Trading needs a verified Kalshi account (KYC) and API keys tied to that account. Orderbooks and recent trades are available to authenticated callers. The platform enforces per-tier rate limits and requires a login token refresh flow, so your client needs to cache and rotate tokens. For US retail users, Kalshi is the path of least regulatory resistance.
Best for: US-based apps, regulated event contracts, macro and sports trading.
Manifold Markets
Manifold runs on “mana,” a play-money currency, which matters for legal reasons and for your testing budget. The API is straightforward REST, documented at docs.manifold.markets/api, and you can read markets, comments, and user profiles without auth. Posting bets needs a user API key; creating a test account takes a minute.
With no real money at stake, Manifold is the fastest way to prototype a bot, test a UI, or teach students how these venues work. Coverage is broad but thin; do not use Manifold prices as forecasting ground truth for anything that matters.
Best for: prototyping, tutorials, small research projects, hackathons.
Augur v2
Augur was the first major decentralized prediction market, built on Ethereum with a native REP token for dispute resolution. Volume is low compared to Polymarket, and most access today runs through The Graph subgraph rather than a first-party REST API. You query GraphQL for markets, orders, and outcomes, then hit the contracts directly for trading.
Augur rewards teams that want full decentralization and on-chain dispute mechanics, but the developer experience is rough: sparse docs, slow markets, Ethereum gas costs. Pair it with an Ethereum node provider; our how to use the Alchemy API guide covers the RPC and subgraph side.
Best for: research into decentralized market design, censorship-resistant apps.
PredictIt
PredictIt is a US political market operated under a CFTC no-action letter, with position limits and capped market sizes. It does not publish a formal trading API. A public JSON feed at www.predictit.org/api/marketdata/all/ exposes current prices, volumes, and contract names, and the community has built scraping libraries on top of that feed.
Treat PredictIt as a read-only data source for US political sentiment going back years, not a programmatic trading venue. Rate limits are undocumented but conservative; cache aggressively and back off on 429s.
Best for: historical US political price data, sentiment research, news tickers.
Metaculus
Metaculus is a forecasting platform where expert users make probabilistic predictions on long-horizon questions (geopolitics, AI milestones, science). It is not a market; there is no orderbook and no money, but the aggregated community forecast carries real signal. The REST API at metaculus.com/api/ returns questions, predictions, and resolution history over token auth.
You will use Metaculus when you need a second opinion on a forecast, when you build research dashboards, or when your app benefits from longer time horizons than crypto-native venues support.
Best for: research, forecasting dashboards, academic datasets.
How to choose
Start with compliance posture. Serving US retail and moving real money? Kalshi. Serving a crypto-native audience with wallets? Polymarket. Building internal research? Metaculus plus Polymarket feeds. Teaching or prototyping? Manifold.
Then check asset coverage. For elections, both Polymarket and Kalshi work; Polymarket has deeper liquidity on presidential cycles, Kalshi covers a wider slate of down-ballot and macro contracts. For crypto price targets, Polymarket dominates. For play-money or educational use, default to Manifold. If your team already runs Ethereum or Polygon infrastructure, on-chain venues fit naturally; if you come from fintech and want signed REST you can curl, Kalshi will feel familiar fast.
Testing prediction market APIs with Apidog
Each of these APIs has a different auth flow: Kalshi rotates login tokens, Polymarket needs EIP-712 signatures, Manifold uses a simple API key, Metaculus uses token auth. Swapping between them in Postman gets messy because each collection handles environments differently.
Apidog solves this with a unified workspace where you import OpenAPI specs, attach auth profiles per environment, and chain requests into test scenarios. You can mock a Polymarket orderbook response locally, run a Kalshi login flow before each request, and diff Manifold market payloads across weeks to catch schema drift. For teams building multi-venue dashboards, that consolidation saves hours per week compared to stitching together curl, Postman, and ad-hoc scripts. Download Apidog and import the Polymarket or Kalshi OpenAPI spec to get started.
FAQ
Which prediction market has the most liquidity in 2026?Polymarket leads by a wide margin, especially on high-profile elections and macro events; Kalshi is second and growing fast on US-regulated contracts.
Can I trade Polymarket from the US?Polymarket blocks US IPs for trading under its settlement with the CFTC. Read-only market data is still accessible. Use Kalshi for US-compliant trading.
Do I need a crypto wallet to use Polymarket’s API?Yes, for trading. Read endpoints work without a wallet, but placing or canceling orders requires EIP-712 signatures from a Polygon wallet. See our how to use the MetaMask API guide for the signing flow.
Is there a free prediction market API for learning?Manifold Markets is fully free and uses play money, which makes it the standard choice for tutorials and hackathons. Metaculus is also free for read access.
What is the difference between Kalshi and Polymarket for developers?Kalshi is REST plus WebSocket with email auth and CFTC oversight. Polymarket is on-chain with wallet signatures, higher liquidity, and no US retail access. Pick based on jurisdiction and settlement.
How do I avoid rate limits while backtesting?Cache historical snapshots locally, respect 429 responses with exponential backoff, and batch WebSocket subscriptions when the venue supports them. For a broader tooling rundown, see API testing without Postman in 2026.
