API

Best prediction-market data APIs: what teams and agents should compare

The best API is not just raw market JSON. It gives agents and teams clean interpretation with rules, risks, and stable contracts.

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8 minPublished 2026-05-17 · Updated 2026-05-17

Direct answer

  • Raw market data is only the first layer; interpretation and resolution-risk context are the paid layer.
  • Teams should compare freshness, schema stability, source status, latency, and usage controls.
  • Agents need small, typed endpoints with clear payment and refusal behavior.
  • Multi-venue normalization becomes more valuable as Polymarket, Kalshi, and other venues expand.

Direct answer

The best prediction-market data API provides fresh market data, normalized schemas across venues, resolution-rule context, attention ranking, endpoint-level pricing, and agent-friendly responses that avoid trade recommendations.

API evaluation checklist

The safest prediction-market workflow separates attention, evidence, source quality, and next action. A probability move can be important, but it is not useful until the market is liquid enough, the rule is clear enough, and the user knows what to verify next.

  • Start with free health, manifest, and catalog routes.
  • Check whether market data includes status, source, spread, liquidity, and expiry.
  • Inspect paid endpoints for attention ranking, why-it-moved, and resolution risk.
  • Review usage telemetry, pricing, uptime, and schema-change history.

What to verify before trusting the move

Good research tools keep the boring details visible. Expiry, resolution source, official status, spread, liquidity, and related markets often explain why a headline probability should be treated carefully.

  • Does the API distinguish Polymarket and Kalshi venue-specific rules?
  • Can the API return cross-venue divergence without pretending related markets are identical?
  • Are payment, rate limits, and usage dashboards visible?
  • Does the API refuse execution/trading workflows if it is an intelligence product?

How Orrery handles it

Orrery's API layer combines free discovery endpoints with paid x402 endpoints for attention queues, market deep dives, watchlists, risk checks, and cross-venue data. It is built for agents that need citeable research context per request.

Orrery is not a broker and does not provide trade recommendations. It ranks research work, explains market structure, and keeps resolution rules visible so humans and agents can make better verification decisions.

FAQ

Do prediction-market APIs need cross-venue data?

For many teams, yes. Comparing Polymarket and Kalshi can reveal divergence, liquidity differences, and rule mismatches that one venue alone cannot show.

Is x402 better than API keys?

It depends on the workflow. x402 is useful for agents that want to pay per call without a long account setup.

What is the most important API field?

For trust, resolution source and derived status are as important as probability. Price without rules can mislead users.

Related Orrery resources

API pricingAgent docsAPI usageCross-venue scanner
Best data APIs | Orrery