Read API vs. Trade API
If you are a developer in today’s prediction market API ecosystem, you can choose from read and trade APIs, and the most reliable choice depends on your needs. You must establish whether you need a single integration or separate integrations for multiple prediction markets.
Read APIs for Market Data Access
A read API is the right option if your goal is to access market data, such as volume, order book depth, prices, and historical data. You can also use read APIs to retrieve market metadata, including category, resolution criteria, and close data. Such APIs can be helpful if you want to create market dashboards or represent data visually, aggregate data from multiple prediction markets, train models on historical outcomes, track market prices, or develop research tools. Developers usually need a basic API key for read API authentication, and trading permissions are typically not required in this case.
Trade APIs: Programmatic Order Execution
A trade API provides programmatic access to order books, cancellations, and position management. To use these tools as a developer, you need full authentication and credentials for wallet signing and access to crypto-native platforms. Trade APIs are the right choice for automated trading, arbitrage execution on multiple platforms, programmatic portfolio management, and trading tool development. In case you prefer a regulated platform like Kalshi, additional verification may be required in addition to a standard API key. Therefore, you should read the selected platform’s developer documentation to understand the requirements.
Why the Distinction Matters
Let’s say you want to access market data, but you end up choosing a trade API. Potential friction points in this scenario include additional authentication steps, stricter rate limits, compliance issues on regulated platforms, and a delayed onboarding process.
Platform API Comparison: Kalshi, Polymarket, and Manifold
While there are many options, we have compared the top prediction market APIs below, with their infrastructure and features confirmed from their official documentation.
Kalshi APIs
Kalshi differentiates itself from other options as the only prediction market platform regulated by the Commodity Futures Trading Commission (CFTC) in the United States.
- API types available: Kalshi offers read and trade APIs, and its architecture consists of a REST API, WebSocket API, and FIX protocol.
- Authentication: Traditional API keys with RSA-signed requests.
- Rate limits: Token-based limits with different budgets for read and write buckets. Most requests cost 10 tokens.
- Pricing and Access Tiers: With Kalshi’s per-second token bucket system, token budgets and rate limits depend on your current tier.
- Streaming/WebSocket API: Developers can use Kalshi’s WebSocket API to access real-time data.
- Key differentiator: Since the platform operates under strict CFTC rules, Kalshi’s API meets the highest exchange and regulatory standards in the US.
- Honest limitation: Additional verification may be needed if you want to access Kalshi’s trading API.
Polymarket
Polymarket is the most popular crypto-native platform with prediction markets as part of the Polygon ecosystem.
- API types available: Gamma API (the primary API for accessing market data), CLOB API for trading activities, and data API for order book data and trade history.
- Authentication: Gamma and Data APIs are fully public, which means that no authentication is required to sign in. On the other hand, the CLOB API has both authenticated and public endpoints.
- Rate limits: Polymarket’s rate limits vary by API and endpoint.
- Pricing and access tiers: Gamma, Data, and CLOB read access are free to use. There are no additional costs to access on-chain data through Polygon directly, but you will require separate indexing infrastructure.
- Streaming/websocket: Public WebSocket is available for real-time order book updates.
- Key differentiator: With the CLOB API, Polymarket has the capacity to cover a wide range of political and crypto events in the prediction space.
- Honest limitation: The Polymarket API is restricted in some jurisdictions, so you must first check for availability in your geographic location.
Manifold
Manifold is a social prediction market known for its play-money betting options.
- API types available: REST API with public and authenticated endpoints.
- Authentication: While read APIs are generally public, APIs associated with registered user accounts require API keys for authentication.
- Rate limits: 500 requests per 60 seconds per IP address.
- Pricing and access tiers: The REST API is free to use.
- Streaming/websocket: A real-time websocket server allows you to receive market, bet, and event-related updates.
- Key differentiator: Since Manifold’s API mainly focuses on non-financial sectors, it’s suitable for conducting research and data training in a variety of markets.
- Honest limitation: Manifold does not cover financial markets the way Kalshi and Polymarket do because its contract structures and users do not match those of other platforms.
Cross-Platform Data Normalization: The Challenge No Competitor Addresses
When it comes to disadvantages, prediction market APIs present data normalization challenges faced by developers who want to create applications that work across multiple platforms.
The Core Problem
Every platform in the prediction market API ecosystem has its own way of structuring each real-world event, such as CFTC-standard market identifiers on Kalshi, Polygon contract addresses on Polymarket, or easy-to-understand URLs on Manifold. With such significant differences, a developer who aims to create a cross-platform aggregation application will have to deal with mismatches at different levels.
What Normalization Requires
If you intend to build a unified pipeline for multiple prediction markets and address the complexity of normalization, you must standardize a cross-platform layer. This means mapping a market identifier to a common event ID and considering the outcome structure, resolution source, timestamp, and settlement currency. For the best outcomes, we advise developers to create the normalization layer before moving to the data aggregation stage.
How to Connect to a Prediction Market API for the First Time
From documentation to releasing a market-ready product, developers only need to follow four steps to connect to their preferred prediction market API.
Before reading the documentation, decide whether you want programmatic order execution or access to real-time market data only, such as prices and outcomes. Keep in mind that the authentication requirements for read and trade APIs are not the same. By choosing the right type, you will avoid unnecessary friction when you reach the authentication phase.
Storing your details is important because most platforms will not let you regenerate your key, and you are most likely to see it once after generation. This is especially critical if you plan to use the credentials in trading bots, where exposed keys carry added risk.
Start testing the prediction market API by making a single request to a read endpoint, such as a market list. This should be done before writing the application logic. The initial test also entails confirming that authentication works as expected and evaluating the response schema.
Based on your access level, confirm the platform’s rate limit and implement an effective exponential backoff strategy for handling HTTP 429 errors. You should also handle 401 and 403 authentication failures for API keys and wallet sessions. Prediction market API rate limits and authentication can change without notice, so proper handling of errors is paramount.
Pros and Cons of Prediction Market Data APIs
Unlike traditional financial data providers, prediction market APIs will give you programmatic access to real-time probability data, but APIs are more likely to face standardization and stability issues.
Pros
Quick access to real-money probability data
Exchange-grade data at Kalshi, a platform regulated by the CFTC
Access to crypto and political event books via Polymarket’s CLOB API
Manifold’s API is suitable for research and training in non-financial sectors
Most platforms offer read APIs without hefty costs or trading credentials
You can verify on-chain Polymarket data via Polygon without incurring API costs
Cons
Risk of API schemas, rate limits, and prices changing without notice
Kalshi users may require additional verification to access the trade API
Polymarket trade API is not available to users in some countries
Cross-platform data normalization is needed due to a lack of standardization
Rate limits on basic tiers can restrict applications that require a substantial amount of production data
Indexing infrastructure is needed if you want to access on-chain data
Next Steps
Before starting the prediction market API integration process as a developer, you should first distinguish between read and trade use cases. Finding a platform that covers every use case may not be possible, and the right API for you depends on your needs. Therefore, you must always confirm your use case, check the platform’s current documentation, and test a read endpoint before you start building the application logic.
Frequently Asked Questions About Prediction Market APIs
What Is the Difference Between a Read API and a Trade API?
A read API will let you access market data, such as prices, volume, and historical outcomes, without needing trading permissions. In contrast, a trade API facilitates programmatic order placement with full authentication required. Take note of possible additional eligibility verification on regulated exchanges.
Are Prediction Market APIs Suitable for Production Financial Applications?
Suitability depends on the platform you have chosen and your specific needs. As a CFTC-regulated platform, Kalshi gives you access to exchange-grade data with binding agreements, while crypto-native platforms grant access to deep market data with fewer requirements. For production financial applications, check the SLA, data integrity, and prices.
Does Polymarket Have a Public API?
Polymarket offers a public REST API and a CLOB API. If you are a developer, you can access read endpoints without complicated authentication steps, but geographic restrictions may prevent you from accessing the trade API. You can also access on-chain data directly via Polygon, but you will need separate indexing infrastructure.
