Prediction Markets Scraper — Kalshi + Polymarket

One normalized feed of prediction-market data from the two largest venues. Every item has the same fields whether it came from Kalshi or Polymarket, so you can compare odds, spreads, volume and close times across exchanges without writing two parsers.

• Kalshi — every open (or closed / settled) market via the public trade API: YES/NO bid and ask with sizes, last price, previous price, 24h and lifetime volume, open interest, liquidity, open/close/expiration times, resolution rules, category.
• Polymarket — every active (or resolved) market via the public Gamma API: outcome prices, best bid/ask, spread, last trade, 24h / 1w / lifetime USD volume, liquidity, tags, neg-risk flag, images, CLOB token ids.
• Order books (optional) — top-N YES bids and asks with sizes from each venue's live book.
• Filters — text search, category/tag, status, min 24h volume, min liquidity, closing-within-N-hours, specific Kalshi series or Polymarket tags.
• No login, no proxies, no browser. Both venues publish this data openly; the Actor reads it politely with retries and backoff.

Example output

{
  "venue": "polymarket",
  "title": "Will the Fed decrease interest rates by 25 bps after the September 2026 meeting?",
  "subtitle": "25 bps decrease",
  "eventTitle": "Fed Decision in September?",
  "category": "fomc",
  "tags": ["fomc", "Economic Policy", "Fed Rates", "Politics", "Economy"],
  "status": "open",
  "yesPrice": 0.0035, "noPrice": 0.9965,
  "yesBid": 0.003, "yesAsk": 0.004, "spread": 0.001,
  "volume24h": 5239468.07, "volume": 29217587.62, "volumeUnit": "usd",
  "liquidity": 4433986.18,
  "closeTime": "2026-09-16T00:00:00Z",
  "url": "https://polymarket.com/event/fed-decision-in-september-762/will-the-fed-decrease-interest-rates-by-25-bps-after-the-september-2026-meeting-586",
  "orderbook": { "yesBids": [{ "price": 0.003, "size": 41200 }], "yesAsks": [{ "price": 0.004, "size": 18750 }] }
}

Kalshi items carry the same keys plus seriesId, openInterest, yesBidSize/yesAskSize, canCloseEarly, expectedExpirationTime and result (yes/no once settled). Kalshi volume is reported in contracts (volumeUnit: "contracts"), Polymarket in USD — the field tells you which.

Input

Field	Default	Notes
venues	both	kalshi, polymarket
search	—	substring match on title / subtitle / event title
categories	—	Kalshi categories (Politics, Economics, Sports, …) or Polymarket tag labels (Crypto, Pop Culture, …)
status	open	open, closed, settled, all
minVolume24h, minLiquidity	0	numeric floors
closingWithinHours	—	only markets closing in the next N hours
maxMarketsPerVenue	500	0 = everything (~10k Kalshi, ~5k Polymarket)
includeOrderbook / orderbookDepth	off / 5	one extra request per market
kalshiSeriesTickers	—	e.g. KXBTC, KXFED, KXHIGHNY
polymarketTags	—	tag slugs, e.g. crypto, fomc, nfl

Typical uses

• Cross-venue odds comparison — run with a search term and both venues, sort by yesPrice.
• Volume/liquidity screens — minVolume24h: 100000 on Polymarket, minLiquidity: 10000 on Kalshi.
• Expiry watch — closingWithinHours: 24 on a schedule, feed the dataset into Sheets or a webhook.
• Order-book snapshots — includeOrderbook: true with a series filter, on a 5-minute schedule, for a depth history.
• Research datasets — status: settled, maxMarketsPerVenue: 0, for resolved outcomes with final prices.

Notes

• Polymarket is read in descending 24h-volume order, so a cap keeps the liquid markets. Kalshi is read in exchange order; use kalshiSeriesTickers or categories to target.
• Polymarket result is inferred from final outcome prices on closed markets; Kalshi result is the exchange's own settlement value.
• Kalshi web links point at the series page (the exchange rate-limits deep links); apiUrl gives the exact market.
• A SUMMARY record in the key-value store lists scanned / matched / pushed counts per venue and any API error.

Pricing

Pay per result. One result = one market (with or without order book). Price is shown on the Actor page; the free trial covers a first run.

Support

Open an Issue on the Actor page — API shape changes at either venue get fixed fast.