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What changes when you choose a prediction-market API?
Compare more than endpoint styles. The consequential differences are what a market identifier represents, whether the API exposes historical data and order-book depth, how updates arrive, what is required to authenticate and trade, and what the venue or provider permits you to do with the data.
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- Data only or execution: Reading public market information is a different integration from placing orders or retrieving a user’s account and portfolio data.
- Identifiers and comparability: A market ID, an outcome token ID, and a provider’s cross-market match are not interchangeable. Similar question titles do not prove that two contracts have the same resolution criteria or deadline.
- Operational behavior: Rate limits, streaming recovery, pagination, settlement, and failure handling shape the system you have to build.
- Rights and availability: Data-use terms, fees, eligibility, and jurisdictional availability can differ by venue, product, and user. Verify the current rules for your intended use.
API documentation and terms can change. The comparisons below reflect the official materials described here as of October 4, 2026; confirm current documentation before launch.
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How does Polymarket’s market-data model work?
Discover the market, then keep the outcome token ID
In Polymarket’s official Market Data Overview, an event can group one or more markets, and each market is a tradable question. Outcomes have their own token IDs. For a YES/NO market, select the desired outcome and retain its token ID: it is the key used for price and order-book requests and is also relevant to trading. Market details can include status, trading constraints, and fee information.
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- Discover an event.
- Select the market representing the question you need.
- Choose the YES or NO outcome and retain its token ID.
- Use that identifier for the relevant price or order-book request, or for real-time data where supported by the applicable interface.
That structure means an event identifier alone is not a substitute for the outcome token ID when requesting outcome-specific data. Keep identifiers as distinct fields in your data model rather than treating event, market, and outcome as synonyms.
Choose the interface by task
Polymarket’s current documentation is organized into market data, prices and order books, real-time data, trading, authentication, order management, and fees. Treat discovery, price or depth reads, streaming, and execution as separate integration needs; do not assume one endpoint handles them all. The materials establish that real-time data is documented, but do not establish a complete set of transport, reconnect, snapshot, or delta guarantees for every use case.
How does Polymarket trading authentication differ from reading data?
Polymarket’s official Place Your First Order quickstart illustrates a trading flow using a secure client initialized with a wallet address and signer/private key. The client fetches a market, selects the YES outcome token ID, submits a market order, and waits for settlement. The guide describes settlement as asynchronous and on-chain; this is an example workflow, not a guarantee that every order or account configuration behaves identically.
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Trading therefore adds signer security and an order lifecycle to the data integration. Never put signing secrets in source code or logs. Follow the current wallet and session-key documentation, and build for rejection, partial fills, cancellation, and delayed settlement rather than treating an accepted request as a completed trade.
Polymarket API vs. Kalshi API
Kalshi’s Help Center overview, dated March 10, 2026, characterizes its API as REST. It describes access to public market information, market order books, and selected market statistics, alongside account data such as a user’s orders, trades, portfolio, and portfolio history. Kalshi’s official API reference includes a market order-book GET operation and an order-submission POST operation.
| Developer question | Polymarket | Kalshi |
|---|---|---|
| Market structure and identifiers | Events group markets; each market has outcomes with separate token IDs. The outcome token ID is used for outcome-specific prices, order books, and trading. Source: Polymarket, Market Data Overview. | Market information and order-book operations are documented. Identifier mapping details are not stated in the cited Kalshi overview and endpoint references. |
| Market data and order books | Market-data and price/order-book documentation is available. Market details can include status, trading constraints, and fees. Source: Polymarket, Market Data Overview. | The Help Center overview describes public market data and selected statistics; the official reference documents a market order-book GET operation. |
| Account and execution operations | The quickstart demonstrates submitting an order through a wallet-backed client and waiting for asynchronous on-chain settlement. Source: Polymarket, Place Your First Order. | The Help Center overview describes access to a user’s orders, trades, portfolio, and portfolio history; the API reference documents an order-submission POST operation. |
| Authentication and signing | The cited quickstart uses a wallet address and signer/private key. Exact behavior can vary by account configuration; consult current authentication documentation. | Not stated in the cited Help Center overview and endpoint references. Check current authentication documentation. |
| WebSocket availability and streaming details | Documentation includes a real-time data area; specific transport behavior and guarantees are not stated in the cited overview and quickstart. | Not stated in the cited Help Center overview and endpoint references. |
| Rate limits, eligibility, and fees | Market details may include fee information. Comparable rate-limit and eligibility values are not stated in the cited overview and quickstart. | Comparable rate-limit, fee, and eligibility values are not stated in the cited Help Center overview and endpoint references. |
Choose between them based on the venue your users need and the exact operations your product requires, then verify the live authentication model, market identifiers, request limits, streaming support, trading rules, fees, and eligibility in that venue’s current documentation. REST availability by itself does not establish equivalent data coverage or trading behavior.
What does Manifold’s API offer, and what should developers watch?
Manifold’s official API documentation names api.manifold.markets as its API host. It describes REST access and a WebSocket endpoint with market and global event subscriptions. Some operations are unauthenticated; others accept an API key or bearer JWT.
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- Rate limit: Manifold states a limit of 500 requests per minute per IP. Treat that as Manifold’s documented technical limit, not a general allowance for other APIs, and recheck it before deployment.
- Maturity: The documentation labels the API alpha and warns that it can change or break. Plan for interface changes and test integrations against current behavior.
- Data use: The licensing section permits bots, automated trading systems, algorithmic tools, and integrations. It prohibits scraping outside the API and rate-limit circumvention; commercial AI/ML training on API data requires a data license. Confirm the current terms for your specific use.
Manifold’s stated transport and access options may fit a prototype or product centered on its markets, but alpha status and data-use restrictions are architectural considerations, not footnotes to resolve after launch.
When does a unified provider make sense?
Prediction.com documents a unified prediction-market API covering multiple venues, with REST, WebSocket, and MCP interfaces. Its documentation lists market, price and history, order-book, trades, cross-market matching, and analytical endpoints, as well as API-key setup and service plans.
A provider can reduce the number of direct venue integrations and offer normalized access where a product needs cross-venue data. That convenience creates a provider dependency: your coverage, identifiers, latency, availability, terms, and costs now depend in part on its implementation. “Unified” does not by itself establish that instruments are equivalent, updates are immediate, or the provider has the same data rights as each venue.
Before relying on normalized results, test matching against the exact questions your application compares. Check resolution criteria and deadlines, historical coverage, update latency, outage behavior, license scope, and total cost. Decide what your application should do if the provider is unavailable or a market mapping is missing or ambiguous.
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For a Polymarket-only data product
Start with the official market-data documentation. Model event, market, and outcome separately, and preserve outcome token IDs as first-class identifiers. Add only the price, order-book, or real-time interfaces your product needs.
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For trade execution
Read the chosen venue’s current authentication, order lifecycle, fee, and settlement documentation before writing order code. Keep signing secrets out of source and logs; handle rejected, partially filled, canceled, and asynchronously settled orders as distinct states.
For cross-venue analytics
Decide whether to integrate venues directly or use a provider’s normalized layer. Validate market matching for the exact instruments and criteria being compared; titles alone are not a reliable equivalence test. Include an explicit fallback or degraded mode for provider or venue outages.
For high-frequency or resilient services
Verify each API’s current request limits, WebSocket reconnect behavior, snapshot-versus-delta semantics, pagination, status and incident channels, and data rights. Do not infer these behaviors for one venue from another venue’s documentation.
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Review the relevant venue and provider terms before storing, redistributing, or using data to train models. Manifold’s documentation specifically distinguishes API use from a commercial AI/ML training-data license; other services’ terms need separate review.
What the comparison does not settle
The cited materials do not establish comparable rate limits, WebSocket guarantees, authentication details, fees, eligibility, or jurisdictional availability across all the platforms discussed. Those are product- and venue-specific facts to confirm in current official documentation and terms for the countries and users you intend to serve. Do not assume that access to an API means that every user may trade, or that API access grants unrestricted rights to store or redistribute its data.
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