Best Prediction Market APIs for Developers: Complete Guide

Why Prediction Market APIs Matter

Prediction markets processed over $44 billion in trading volume in 2025. Behind that volume sits a growing ecosystem of automated traders, analytics platforms, and custom applications—all powered by APIs.

Whether you’re building arbitrage bots, portfolio trackers, research tools, or trading algorithms, understanding the available APIs is essential. Each platform offers different capabilities, authentication methods, rate limits, and data access levels.

This guide covers the major prediction market APIs, comparing their features, limitations, and best use cases for developers.

Polymarket API

Polymarket is the largest prediction market by volume, processing billions in monthly trades. Its API ecosystem is the most comprehensive, offering multiple services for different needs.

API Architecture

Polymarket’s API is split into several components:

• CLOB API: The Central Limit Order Book API handles trading operations—placing orders, canceling orders, and retrieving order book data.
• Gamma API: Provides market metadata including market details, resolution criteria, and category information.
• Data API: Returns user-specific data like positions, trade history, and portfolio information.
• WebSocket API: Real-time streaming for order book updates, price changes, and trade executions.

Authentication

Polymarket uses a two-level authentication system:

Level 1 (L1) – Wallet Signature: Uses EIP-712 typed data signatures on Polygon. You sign a message with your Ethereum wallet to prove ownership. This provides read access and basic trading capabilities.

Level 2 (L2) – API Credentials: For higher-rate trading, you generate API credentials from your L1 authentication. These use HMAC-SHA256 signatures for each request, providing faster authentication without wallet signing per request.

Required headers for authenticated requests include POLY_SIGNATURE, POLY_API_KEY, and POLY_TIMESTAMP.

Rate Limits

Polymarket implements tiered rate limiting:

• Free tier: 1,000 calls per hour for non-trading queries
• Premium ($99/month): WebSocket access, 30+ days historical data, priority support
• Enterprise ($500+/month): Dedicated nodes, no throttling, custom limits

The platform uses throttling rather than hard rejection—requests are queued and delayed rather than dropped when limits are approached.

Key Endpoints

Base URL: https://clob.polymarket.com

Endpoint	Method	Description
/markets	GET	List all markets with metadata
/prices	GET	Current prices for specified tokens
/orderbook	GET	Order book depth for a market
/orders	POST	Place a new order
/orders/{id}	DELETE	Cancel an existing order

Official SDK

Polymarket provides official SDKs via their GitHub repo:

• Python: py-clob-client (PyPI: pip install py-clob-client)
• TypeScript: @polymarket/clob-client
• Rust: rs-clob-client

The Python client is the most popular, with 590+ GitHub stars and active maintenance.

Code Example

from py_clob_client.client import ClobClient

# Read-only access (no authentication needed)
client = ClobClient("https://clob.polymarket.com")
markets = client.get_markets()
price = client.get_price(token_id, side="BUY")

# Authenticated trading
client = ClobClient(
    host="https://clob.polymarket.com",
    key=PRIVATE_KEY,
    chain_id=137,
    signature_type=1
)
order = client.create_order(...)

Best For

Polymarket’s API is ideal for high-volume trading bots, arbitrage systems, and analytics platforms that need deep market data. The WebSocket support makes it suitable for latency-sensitive strategies. International traders benefit from near-zero fees.

Kalshi API

Kalshi is the only CFTC-regulated prediction market exchange in the United States. Its API is designed for institutional-grade trading with multiple connection options.

API Architecture

Kalshi offers three connection methods:

• REST API: Standard HTTP endpoints for all operations
• WebSocket API: Real-time streaming for market data and order updates
• FIX Protocol: Industry-standard Financial Information eXchange protocol for institutional trading

The FIX 4.4 implementation is notable—it’s the same protocol used by major stock and futures exchanges, making integration straightforward for firms with existing trading infrastructure.

Authentication

Kalshi uses token-based authentication:

1. Request a session token using your API key and secret
2. Include the token in subsequent request headers
3. Tokens expire every 30 minutes—implement automatic refresh

For trading operations, you’ll also need to sign requests with your private key. The authentication flow is more traditional than Polymarket’s blockchain-based approach.

Rate Limits

Kalshi implements tiered rate limits based on account type:

• Standard accounts have baseline limits
• High-volume traders can request limit increases
• Best practice: implement exponential backoff and request caching

Unlike Polymarket, Kalshi doesn’t charge for API access—you only pay trading fees (currently 0% for API trades, subject to change).

Key Endpoints

Base URL: https://api.kalshi.com/v1 (Production) | https://demo-api.kalshi.com/v1 (Sandbox)

Endpoint	Method	Description
/markets	GET	List available markets
/events	GET	List event categories
/portfolio	GET	User positions and balances
/orders	POST	Place new orders
/orders/{id}	DELETE	Cancel orders

Official SDKs

Kalshi provides official SDKs for the most popular languages:

• Python (sync): pip install kalshi_python_sync
• Python (async): pip install kalshi_python_async
• TypeScript: Official SDK for Node.js and browser environments

Note: The older kalshi-python package is deprecated. Both official SDKs include RSA-PSS authentication with automatic request signing, type-safe models, and comprehensive error handling.

Community options also exist for other languages:

• Go: github.com/ammario/kalshi
• Data pipelines: dltHub Kalshi source

Code Example

import requests

# Authentication
auth_response = requests.post(
    "https://api.kalshi.com/v1/login",
    json={"email": EMAIL, "password": PASSWORD}
)
token = auth_response.json()

# Get markets
headers = {"Authorization": f"Bearer {token}"}
markets = requests.get(
    "https://api.kalshi.com/v1/markets",
    headers=headers
).json()

Best For

Kalshi’s API is ideal for US-based traders who need regulatory clarity, institutional traders familiar with FIX protocol, and applications requiring structured event contract data. The sandbox environment makes development and testing straightforward.

For traders building cross-platform systems, understanding both Polymarket and Kalshi APIs enables arbitrage strategies that exploit price differences between venues.

Manifold Markets API

Manifold Markets operates differently—it uses play money (Mana) rather than real currency. However, its open API makes it valuable for prototyping, research, and learning.

API Architecture

Manifold provides a REST API with public and authenticated endpoints:

• Public endpoints: Market data, user profiles, topics—no authentication required
• Authenticated endpoints: Betting, market creation, portfolio management

Documentation is available at docs.manifold.markets/api.

Authentication

Generate an API key from your Manifold profile. Include it in requests via the Authorization header. Each account gets one API key.

Rate Limits

Manifold allows 500 requests per minute per IP address—generous compared to real-money platforms.

Key Endpoints

Endpoint	Method	Description
/markets	GET	List markets with filters
/market/{id}	GET	Single market details
/bet	POST	Place a bet (authenticated)
/market	POST	Create a market (authenticated)

Best For

Manifold’s API is perfect for prototyping prediction market applications before deploying to real-money platforms, academic research on prediction market dynamics, and learning API development without financial risk.

Metaculus API

Metaculus is a forecasting platform rather than a trading market. It focuses on aggregating predictions for research and decision-making rather than financial outcomes.

API Access

Metaculus provides API access primarily for research partners. The API returns question data, forecast distributions, and resolution information.

Documentation is available at metaculus.com/api/ with a Swagger/OpenAPI spec.

Key Features

• Question metadata and resolution criteria
• Aggregate forecast distributions
• Historical prediction accuracy data
• Community prediction breakdowns

Best For

Metaculus is ideal for researchers studying forecasting accuracy, applications that aggregate predictions from multiple sources, and projects focused on long-term forecasting rather than trading.

PredictIt API

PredictIt is an older prediction market focused on US politics. Its API capabilities are limited compared to newer platforms.

API Access

PredictIt offers a basic public endpoint:

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

This returns current prices for all markets. However, there’s no trading API—all trades must go through the web interface.

Historical Data

Historical data requires CSV downloads rather than API access. Third-party libraries (rpredictit for R, predictit for Python) wrap the available endpoints.

Limitations

• Read-only API (no programmatic trading)
• Limited historical data access
• Non-commercial use license
• Updates approximately every minute

Best For

PredictIt’s API is suitable for political prediction tracking, research projects with non-commercial licenses, and simple market monitoring applications.

Aggregated API Solutions

Several services aggregate data from multiple prediction markets, simplifying multi-platform development.

FinFeedAPI

FinFeedAPI provides a unified API for Polymarket, Kalshi, Myriad, and Manifold Markets.

Key Features:

• Single integration for multiple platforms
• Normalized data format across markets
• Real-time and historical data
• Subscription-based pricing

This is valuable for applications that need cross-platform data without managing multiple API integrations.

Bitquery

Bitquery offers a GraphQL API for Polymarket blockchain data, enabling complex queries across on-chain trading activity.

Key Features:

• GraphQL query flexibility
• Blockchain-level granularity
• Wallet activity tracking
• Historical trade data

Oddpool

Oddpool aggregates odds across prediction market venues, identifying cross-venue price discrepancies.

Key Features:

• Cross-venue odds comparison
• Arbitrage opportunity detection
• Historical spread tracking
• API access for developers

API Comparison Matrix

Feature	Polymarket	Kalshi	Manifold	PredictIt
Trading API	Yes	Yes	Yes (play money)	No
WebSocket	Yes (paid)	Yes	Limited	No
FIX Protocol	No	Yes	No	No
Official SDK	Python, TS, Rust	Python, TS	Partial	No
Rate Limits	1k/hr free	Tiered	500/min	~1/min
Auth Method	Wallet + HMAC	Token + Private Key	API Key	None
Geographic	Global*	US only	Global	US focused
Settlement	USDC (Polygon)	USD	Mana (play)	USD

*Polymarket has geographic restrictions in certain countries

Choosing the Right API

Your choice depends on your specific requirements:

For high-frequency trading: Polymarket’s WebSocket API or Kalshi’s FIX protocol provide the lowest latency. Both support real-time streaming essential for algorithmic trading strategies.

For US regulatory compliance: Kalshi is the only CFTC-regulated option with full API trading support.

For prototyping: Manifold Markets offers generous rate limits and no financial risk for testing ideas.

For research: Metaculus provides forecasting data with academic rigor; PredictIt offers political market history.

For cross-platform applications: FinFeedAPI or custom integrations with multiple platforms provide the broadest coverage.

WebSocket Implementation Guide

Real-time data is critical for prediction market applications. Here’s how WebSocket implementations differ across platforms.

Polymarket WebSocket

Endpoint: wss://ws-subscriptions-clob.polymarket.com

Polymarket’s WebSocket supports two channel types:

• User channel: Personal order updates, trade confirmations, position changes
• Market channel: Order book updates, price changes, trade feed

Available events include:

• book: Order book depth changes
• price_change: Last traded price updates
• tick_size_change: Market parameter changes
• last_trade_price: Most recent execution price

WebSocket access requires a premium subscription ($99/month or higher). The connection uses JSON messages for subscriptions and updates.

Kalshi WebSocket

Kalshi’s WebSocket provides similar functionality with different authentication:

1. First authenticate via REST to obtain a session token
2. Connect to the WebSocket endpoint with the token
3. Subscribe to specific markets or event categories

The WebSocket streams market updates, order book changes, and trade executions without polling overhead. This is essential for latency-sensitive trading strategies.

Connection Management

Robust WebSocket implementations need:

• Heartbeat handling: Send periodic pings to keep connections alive
• Automatic reconnection: Detect disconnections and reestablish connections
• Message queuing: Buffer messages during reconnection to prevent data loss
• Subscription restoration: Re-subscribe to channels after reconnecting

Authentication Deep Dive

Authentication is where most developers encounter initial friction. Here’s a detailed breakdown of each platform’s approach.

Polymarket Authentication Flow

Polymarket’s blockchain-based authentication has several steps:

1. Generate a signing message: Create an EIP-712 typed data structure with your wallet address and timestamp
2. Sign with your wallet: Use your Polygon wallet private key to sign the message
3. Exchange for API credentials: Submit the signature to receive API key and secret
4. Sign requests: Use HMAC-SHA256 with your secret to sign each authenticated request

The domain for EIP-712 signing is “ClobAuthDomain” with version “1” on chain ID 137 (Polygon mainnet).

This approach ensures only wallet owners can trade, but adds complexity compared to traditional API key systems.

Kalshi Authentication Flow

Kalshi uses more traditional authentication:

1. Obtain API credentials: Generate key and secret from your Kalshi account dashboard
2. Request session token: POST to /login with credentials
3. Include token in headers: Add “Authorization: Bearer {token}” to requests
4. Refresh before expiration: Tokens expire after 30 minutes—refresh proactively

For trading operations, you may also need to sign requests with your private key depending on the operation type.

Security Considerations

Prediction market API credentials control real money. Follow these security practices:

• Environment variables: Never hardcode credentials in source files
• Secret management: Use services like AWS Secrets Manager or HashiCorp Vault for production
• Key rotation: Periodically regenerate API keys
• IP whitelisting: If supported, restrict API access to known IP addresses
• Minimal permissions: Only request the access levels you need

Development Best Practices

When building prediction market applications, follow these guidelines:

Handle rate limits gracefully: Implement exponential backoff, cache responses where appropriate, and respect platform limits. Getting blocked hurts more than slowing down.

Implement proper error handling: APIs return various error codes. Handle authentication failures, rate limits, and market-specific errors (closed markets, insufficient funds) appropriately.

Use WebSockets for real-time data: Polling REST endpoints wastes resources and introduces latency. WebSocket connections provide instant updates when available.

Secure your credentials: Store API keys in environment variables, never commit them to repositories, and rotate keys periodically. Prediction market credentials control real money.

Test in sandbox first: Kalshi provides a sandbox environment. For Polymarket, test with small amounts on mainnet or use Manifold for logic validation.

Infrastructure for API Applications

Production prediction market applications demand infrastructure that matches the always-on nature of these markets. Your API integration is only as reliable as the server running it.

Why Dedicated Infrastructure Matters

API rate limits, WebSocket connections, and real-time data streams require consistent uptime. A dropped connection during a volatile market event means missed opportunities. Home internet connections introduce latency spikes and reliability issues that production trading systems can’t tolerate.

For Polymarket traders, network proximity to Polygon nodes directly impacts transaction confirmation times. Every millisecond counts when competing for order book positions or executing time-sensitive trades.

Platform-Specific Requirements

Polymarket applications benefit from servers with direct connectivity to Polygon RPC nodes. Faster block confirmation means quicker trade execution and reduced slippage on order placement.

Kalshi applications need reliable US-based infrastructure for optimal latency to their exchange servers. The FIX protocol connections particularly benefit from stable, low-latency networking.

Recommended Specifications

• CPU: Minimum 2 cores for API polling; 4+ cores for WebSocket processing and bot logic
• RAM: 4GB minimum; 8GB+ for applications maintaining multiple WebSocket connections
• Storage: SSD required for logging and local data caching
• Network: 1Gbps with burst capability; low-latency routing to financial infrastructure
• Uptime: 99.9%+ guaranteed—markets don’t pause for server maintenance

NYCServers provides VPS solutions specifically configured for prediction market trading. Our Polymarket VPS offers optimized connectivity to Polygon infrastructure, while our Kalshi VPS delivers the US-based, low-latency environment that regulated exchange access demands.

Build Your Prediction Market Application

The prediction market API ecosystem has matured significantly. Polymarket and Kalshi offer institutional-quality APIs. Aggregation services simplify multi-platform development. Developer tools and SDKs reduce implementation time.

For applications requiring continuous operation, dedicated infrastructure makes the difference between capturing opportunities and watching them pass. Whether you’re running arbitrage bots across platforms or building analytics dashboards that need real-time data, the right VPS foundation ensures your code performs when it matters.

Common Integration Challenges

Developers frequently encounter these issues when integrating prediction market APIs:

Blockchain confirmation delays: Polymarket transactions require blockchain confirmations. Orders may appear pending for several seconds. Design your application to handle asynchronous order states rather than expecting instant confirmation.

Market resolution timing: Markets resolve based on real-world events, not fixed schedules. Your application needs to handle markets that remain open longer than expected or resolve at unexpected times.

Liquidity variations: Order book depth varies dramatically between markets. Popular events have tight spreads; niche markets may have wide spreads or no liquidity. Check available liquidity before placing large orders.

Data normalization: Each platform formats data differently. Market identifiers, price formats, and timestamp conventions vary. Build normalization layers if integrating multiple platforms.

Geographic restrictions: Polymarket has country-specific restrictions. Kalshi is US-only. Your application needs to handle these restrictions gracefully, either by checking user location or providing appropriate messaging.

Frequently Asked Questions

Do I need to pay for prediction market API access?

Basic API access is free on most platforms. Polymarket charges for premium features like WebSocket access ($99/month). Kalshi’s API is free—you only pay trading fees. Manifold and PredictIt offer free access for their limited capabilities.

Which API is best for beginners?

Manifold Markets has the gentlest learning curve—simple authentication, generous rate limits, and no financial risk. Once comfortable, transition to Polymarket or Kalshi for real-money trading.

Can I trade on both Polymarket and Kalshi programmatically?

Yes, both platforms support programmatic trading. Polymarket uses blockchain-based authentication while Kalshi uses traditional API keys. You’ll need separate integrations for each, though libraries like predmarket provide unified interfaces.

What programming languages are supported?

Python has the best support across platforms with official and community libraries. JavaScript/TypeScript is supported for Polymarket. Go and Rust have community options for specific platforms. Any language that can make HTTP requests can use the REST APIs.

How do I handle the 30-minute token expiration on Kalshi?

Implement automatic token refresh in your application. Store the token expiration time and request a new token before it expires. Most client libraries handle this automatically.

Is there a sandbox environment for testing?

Kalshi provides a full sandbox at demo-api.kalshi.com. Polymarket doesn’t have a separate testnet—test with small amounts on mainnet or validate logic using Manifold. Always test thoroughly before deploying with significant capital.

What are the main differences between REST and WebSocket APIs?

REST APIs use request-response patterns—you ask for data and receive it. WebSocket APIs maintain persistent connections and push data to you in real-time. For trading applications, WebSocket reduces latency significantly. For occasional data fetching, REST is simpler to implement.

How do I monitor API rate limits in production?

Track rate limit headers returned by each API response. Most platforms include remaining-calls and reset-time headers. Log these values, set alerts for when you approach limits, and implement automatic throttling. For high-volume applications, consider using multiple API keys or upgrading to premium tiers with higher limits.