Kalshi + Polymarket Scraper — Unified Prediction Market Odds & History

Scrape Kalshi and Polymarket prediction markets into one normalized schema: every open market's question, implied probability, volume, liquidity, close date, and category — plus full odds history (Kalshi candlesticks and Polymarket price time-series). Pure JSON APIs under the hood (no browser), so runs are fast and cheap. Export as JSON, CSV, Excel, or XML, or pull results straight through the Apify API into your app, AI agent, model, or spreadsheet.

Prediction markets cleared ~$24B/month in volume (April 2026) and news organizations cite their odds daily — but there's no public cross-platform API. This Actor is that missing layer: a prediction market data feed and probability oracle for analysts, journalists, researchers, traders, and AI agents.

No per-datapoint games, never charged for failures. Flat $2 per 1,000 items ($0.002 each) — and one "item" in history mode is a market's entire time-series, not a point. Failed or empty lookups are never charged.

Two modes

1. Unified markets feed

All open markets from both platforms in one normalized schema. Kalshi coverage scans the full open book (~65k markets, verified at build time); Polymarket arrives volume-ranked from its API. With both platforms selected, results are ranked within each platform by volume and interleaved, so you always see both (a pure cross-platform volume sort would bias toward Polymarket, which reports volume in USD while Kalshi reports it in contracts). Filter by:

• Keyword — "election", "fed", "bitcoin", "world cup"…
• Category — Politics, Economics, Sports, Crypto, World… (matches Kalshi categories and Polymarket event tags)
• Minimum volume — skip dead markets
• Closing within N days — only near-resolution markets
• Platform — both, Kalshi only, or Polymarket only

Sort by one of:

• Volume (default) — ranked within each platform and interleaved
• Closing soon — soonest-resolving first (global, comparable across platforms)
• Biggest movers (24h) — largest YES-price move in either direction first

2. Odds history

Give it Kalshi tickers and/or Polymarket URLs; get each market's price time-series (daily or hourly, up to 365 days): Kalshi native OHLC candlesticks (open/high/low/close + volume), Polymarket CLOB price points. "How did the odds move after the debate?" — answered in one run.

Output example (unified feed)

{
    "type": "market",
    "platform": "kalshi",
    "id": "KXNBAFINALS-26-SA",
    "question": "Will the San Antonio win the 2026 Pro Basketball Championship?",
    "url": "https://kalshi.com/markets/kxnbafinals",
    "yesPrice": 0.21,
    "impliedProbabilityPct": 21,
    "bestBid": 0.2,
    "bestAsk": 0.21,
    "spread": 0.01,
    "oneDayChange": -0.03,
    "volume": 75063434,
    "closeTime": "2026-06-22T03:00:00Z",
    "category": "Sports",
    "tags": ["Sports"],
    "scrapedAt": "2026-06-12T20:31:00.000Z"
}

Output example (odds history)

{
    "type": "history",
    "platform": "polymarket",
    "question": "Will Jesus Christ return before 2027?",
    "resolution": "1d",
    "pointCount": 31,
    "points": [
        { "t": "2026-05-14T00:00:18.000Z", "price": 0.0215 },
        { "t": "2026-06-12T20:31:04.000Z", "price": 0.0205 }
    ]
}

Each feed item also carries platform-native identifiers (kalshi.seriesTicker, polymarket.clobTokenIds, …) so you can chain a feed run straight into a history run.

A probability oracle for AI agents (MCP / LangChain)

Apify Actors plug into agents as tools (MCP). Pointed at this Actor, an agent can answer "What probability do prediction markets give X?" with live, cross-platform odds — and pull the time-series to reason about momentum:

• MCP — expose the Actor as an agent tool via Apify's MCP server
• LangChain / LlamaIndex — call it as a tool from any framework
• n8n / Zapier / Make — scheduled odds snapshots into sheets and alerts; run it daily and you accumulate your own odds archive

Data sources & notes

• Kalshi: official public trade API (/events, /candlesticks) — no auth needed for market data. Prices are decimal dollars (0–1 = implied probability).
• Polymarket: public Gamma + CLOB APIs. Prices 0–1.
• Volume units differ: USD on Polymarket, contracts (≈ $1 notional) on Kalshi. Figures are platform-reported; the cross-platform volume sort treats them as comparable for ranking only.
• Only public market data is accessed — no accounts, no trading, no user data.

FAQ

Is there an official cross-platform prediction market API? No. Kalshi and Polymarket each have their own APIs with different schemas, auth models, and quirks (Kalshi's pagination buries real markets under parlay listings; this Actor handles that). This Actor merges them into one normalized feed.

How much does it cost? $0.002 per stored item — $2 per 1,000. A history item is one market's complete series (up to 365 days of points) for the same $0.002. Failed or empty lookups are never charged. Apify's free $5 monthly credit covers ~2,500 items.

How fresh is the data? Each run fetches live API data. Schedule runs (every hour, daily…) to build snapshots over time.

Can I get resolved-market outcomes? Closed/settled markets are visible in history mode via their tickers/URLs. A dedicated resolutions & calibration feed is on the roadmap.