There is no universally best prediction-market API: choose based on whether you need one venue’s market data, order execution and account operations, or normalized data across several venues. Polymarket’s outcome token IDs are central to its data and trading flow; Kalshi documents REST market and account operations; Manifold offers REST and websocket access but labels its API alpha; and a provider such as Prediction.com can abstract multiple venues at the cost of an additional dependency.
What matters when choosing a prediction-market API?
Start with the product you are building, not with an endpoint list. A market-data dashboard, a trading client, and a cross-venue analytics service have different requirements. The important architectural questions are:
- Coverage and identity: Which venues and instruments do you need, and how will you identify each market and outcome reliably?
- Data shape: Do you need discovery, current prices, history, trades, or order-book depth?
- Execution: Must users place orders or inspect their accounts, or is read-only data enough?
- Transport and operations: Are REST requests sufficient, or do you need streaming updates, reconnect handling, and documented rate limits?
- Rights and eligibility: May you store, redistribute, or use the data for your intended purpose, and can your users access the venue in their jurisdictions?
These choices are venue-, product-, and jurisdiction-specific. API documentation, fees, eligibility, limits, and terms can change; verify the current official materials before launch.
How does Polymarket market data work?
Follow the event-to-outcome hierarchy
Polymarket’s official Market Data Overview describes an event as a grouping that can contain one or more markets. A market is a tradable question, and its YES and NO outcomes each have their own token ID. The practical discovery path is to find an event, choose the market within it, select the outcome, and retain that outcome’s token ID.
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That token ID is the key identifier for price and order-book requests and for trading. Treat it as a first-class identifier in your application rather than relying on a market title or a YES/NO label alone. Market details also include status, trading constraints, and fee information, so discovery should not stop once a title appears to match.
Use the interface for the task
Polymarket’s documentation separates market data, prices and order books, real-time data, trading, authentication, order management, and fees. This organization reflects distinct integration jobs: discovery does not itself provide execution, and a price request is not a substitute for streaming or account operations. The documentation identifies a real-time-data area, but transport details and supported channels should be confirmed in its current documentation rather than inferred from the section name.
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How does Polymarket trading authentication and order flow work?
Polymarket’s official Place Your First Order quickstart illustrates a client initialized with a wallet address and signer/private key. It fetches a market, selects the YES outcome’s token ID, submits a market order, and waits for settlement. The guide says settlement occurs asynchronously on-chain. This is an example integration path, not a guarantee that every order type or account setup has identical behavior.
Keep signing secrets out of source code and logs. Follow the current wallet and session-key documentation for the authentication approach appropriate to your application. Before implementing execution, review the venue’s current authentication, order lifecycle, fees, and settlement documentation. Your state model should explicitly account for rejection, partial fill, cancellation, and asynchronous settlement; do not treat a successful submission request as proof that an order has fully settled.
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Polymarket API vs. Kalshi API, Manifold, and a unified provider
The following comparison distinguishes documented features from details that should be checked directly. “Not stated” means the cited documentation described here does not establish a comparable value; it does not mean the feature is unavailable.
| Integration | Documented data and identifiers | Streaming and execution | Limits, maturity, and terms |
|---|---|---|---|
| Polymarket direct | Events group markets; YES and NO outcomes have separate token IDs used for prices, order books, and trading. The Market Data Overview describes market status, constraints, and fee information. | Documentation is organized into real-time data and trading areas. The quickstart demonstrates wallet-signed order placement and asynchronous on-chain settlement. Specific transport channels and broader account-operation details: verify in current official docs. | Current request limits, eligibility, and data-use terms: not stated in the cited Polymarket materials summarized here; verify current official documentation and terms. |
| Kalshi direct | Kalshi’s Help Center API overview, dated March 10, 2026, describes public market information, order books, selected market statistics, and account data including orders, trades, portfolio, and portfolio history. The official reference exposes a market order-book GET operation. | The overview characterizes the API as REST; the official reference exposes an order-submission POST operation. Authentication details, market identifier mapping, and websocket availability: not stated in the cited materials summarized here. | Current request limits, data-use terms, fees, and eligibility: not stated in the cited materials summarized here. Check updated Kalshi documentation and trading rules. |
| Manifold direct | Official API documentation names api.manifold.markets as the API host. Some operations are unauthenticated; others accept an API key or bearer JWT. |
Documentation describes a websocket endpoint with market and global event subscriptions. Execution and account functionality should be checked against the specific operations your product needs. | Manifold documents a limit of 500 requests per minute per IP and labels the API alpha, warning it can change or break. Its terms allow bots, automated trading systems, algorithmic tools, and integrations; they prohibit scraping outside the API and rate-limit circumvention. Commercial AI/ML training on API data requires a data license. |
| Prediction.com unified API | Provider documentation describes multi-venue coverage, market and price/history data, order books, trades, cross-market matching, and analytical endpoints. | Provider documentation lists REST, WebSocket, and MCP interfaces and describes API-key setup. Confirm the exact coverage and operations needed for your integration. | Service plans are documented by the provider. Independent coverage, latency, license scope, outage behavior, and total cost should be evaluated for your use case. |
When should you integrate directly with a venue?
Choose direct Polymarket access for a Polymarket-only product
If your application only needs Polymarket discovery, prices, or order books, begin with Polymarket’s official market-data documentation and store outcome token IDs alongside your internal records. This keeps venue-specific identifiers explicit and avoids relying on a third-party mapping layer for a single-venue product.
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Choose direct execution when the venue is part of the product
If users will trade, read the venue’s current authentication and order-management materials before designing the client. Build around the venue’s actual order lifecycle and settlement behavior, with error and recovery paths for rejection, partial fills, cancellation, and delayed settlement. Do not reuse one venue’s signing or order assumptions for another.
Use a unified provider when normalization is worth the dependency
A cross-venue provider can reduce the number of direct integrations and offer common data interfaces. That abstraction also becomes a dependency: your product relies on the provider’s market mapping, normalization choices, uptime, coverage, and licensing. Similar-looking titles do not establish that two markets have the same resolution criteria or deadline, so verify instrument matches for the exact comparisons your product presents.
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What should developers verify before launch?
Data quality and real-time behavior
- Confirm the current market identifiers and how outcomes map to them.
- Check whether the required data is current price, historical series, trades, order-book depth, or a combination.
- For streaming, verify the actual channels, snapshot-versus-delta behavior, reconnect procedure, and handling of stale or missing updates.
- Check pagination and request limits rather than assuming they match another venue’s API.
- For a unified provider, test the market matches, historical coverage, update latency, and behavior during venue or provider outages.
Execution and access
- Confirm authentication, signing, key handling, order types, cancellation, fills, and settlement with the current venue documentation.
- Verify fees and trading constraints for the relevant market and account configuration.
- Check current user and jurisdiction eligibility for the venue and product; the documentation summarized here does not establish comparable eligibility across these platforms.
Data rights and operating risk
- Review each venue’s and provider’s terms before storing or redistributing data.
- Manifold explicitly distinguishes API access from a commercial AI/ML training-data license.
- Document your fallback behavior if a venue API, websocket, or third-party abstraction is unavailable, and monitor the relevant status or incident channels.
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