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

Published: 2026-05-17
Updated: 2026-05-17
Canonical: https://orrery.me/blog/best-prediction-market-data-apis
Markdown: https://orrery.me/blog/best-prediction-market-data-apis/markdown

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

## 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 pricing](https://orrery.me/pricing?audience=api)
- [Agent docs](https://orrery.me/docs/agents)
- [API usage](https://orrery.me/api-usage)
- [Cross-venue scanner](https://orrery.me/venues)

Orrery is not affiliated with Polymarket and does not provide investment, legal, or tax advice.