PredScope: what it does, what it costs, where it stops

What it does

The homepage tracks active markets across politics, crypto, sports, economics and culture with an odds calculator, market insights and guides. The compare page lists Polymarket at 0% trading fees, 10,000+ markets, global access and $20B+ all-time volume against Kalshi at roughly 2% on winnings, 2,000+ markets, US only in 42+ states, $3B+ all-time volume and a $25,000 typical max bet.

The API exposes GET /api/markets.json for the top 100 active markets with outcomes, probabilities and volume, GET /api/resolved.json for recent resolutions, and an OpenAPI 3.0.3 spec. No key, CORS enabled, free for commercial, academic and personal use.

• 635 active markets shown when checked, updated every 10 minutes
• Polymarket vs Kalshi and Polymarket vs Robinhood comparison guides
• Free JSON API, no authentication, credit requested if you publish

Pricing

Free. The API page states it is free for any use with no API key. There is no paid tier on the pages checked. The site asks for a credit to PredScope if you publish analysis built on its data.

Venues and data

The homepage names Polymarket, Kalshi, Robinhood, FanDuel and PredictIt. The API documentation says data is sourced from Polymarket's public API only. The comparison pages are written guides with platform attributes, not a live two-venue price feed.

The compare page states that PredScope tracks the platform differences automatically and updates every 10 minutes, so the market counts and volume figures there move over time; the founding years, 2020 for Polymarket and 2021 for Kalshi, do not.

Where it falls short

If you want the same event priced on Kalshi and Polymarket next to each other, this is not that. Prediction Hunt and Oddpool do that; PredScope compares the platforms, then tracks Polymarket prices.

A 10-minute refresh is a research cadence. The top-100 API endpoint is a convenience feed, not a full market dump.

Who should use it

Someone deciding between Polymarket and Kalshi who wants the fee and access differences in one table, and developers who want a free, keyless JSON feed of top Polymarket markets for a dashboard or a bot prototype.