Kalshi & Polymarket Prediction Markets Scraper

Export live prediction-market data from Kalshi and Polymarket into one normalized dataset.

The actor reads each venue's official public API, normalizes each market into one row, filters out zero-value noise, and ranks markets by 24h volume. No browser, no HTML parsing, and no login.

What you get

One row per market with:

• venue: kalshi or polymarket
• event_id, event_title, category
• market_id, market_name, question, subtitle
• status, result
• yes_price, no_price (0 to 1)
• yes_bid, yes_ask, no_bid, no_ask, last_price
• volume, volume_24h, open_interest, liquidity
• close_time
• url
• volume_rank, rank
• fetched_at

volume_24h_source and open_interest_source tell you whether the number came from the market itself or from its parent event. Polymarket publishes 24h volume per market but sometimes only publishes open interest at the event level, so the field is explicit instead of guessed. Polymarket category is null when the API does not attach tags to the event.

How it works

• Kalshi: GET /trade-api/v2/events with with_nested_markets=true. This endpoint excludes multivariate combo events, which is what makes the output useful instead of a wall of zero-liquidity parlays.
• Polymarket: GET /markets from the Gamma API, ordered by volume24hr. Each market carries its own 24h volume plus an embedded event with the id, title and slug used for the event fields and the public URL.
• Both sources are fetched in parallel. If one venue fails, the run still returns the other venue and writes the failure to VENUE_STATUS in the key-value store.
• Markets are filtered by status, optional text query and optional minimum 24h volume, then sorted by 24h volume and capped per venue.

Input example

{
  "includeKalshi": true,
  "includePolymarket": true,
  "query": "",
  "status": "open",
  "maxMarketsPerVenue": 100,
  "scanItemsPerVenue": 1000,
  "minVolume24h": 0
}

Input fields

Field	Type	Default	Meaning
includeKalshi	boolean	true	Read Kalshi.
includePolymarket	boolean	true	Read Polymarket.
query	string	""	Case-insensitive text filter on question, event title, subtitle or category.
status	string	"open"	open, closed or all.
maxMarketsPerVenue	integer	100	Cap after ranking by 24h volume.
scanItemsPerVenue	integer	1000	Items read before ranking: events for Kalshi, markets for Polymarket. Higher means broader coverage and a slower run.
minVolume24h	number	0	Drop markets below this 24h volume.

Output example

One verbatim row from a completed run (38iKr3oiRbdCJA8mc, 2026-10-19), copied exactly as the dataset returned it:

{
  "venue": "kalshi",
  "event_id": "KXPRESNOMD-28",
  "event_title": "2028 Democratic presidential nominee",
  "category": "Elections",
  "market_id": "KXPRESNOMD-28-AELS",
  "market_name": "Will Abdul El-Sayed be the nominee for the Presidency for the Democratic party?",
  "question": "Will Abdul El-Sayed be the nominee for the Presidency for the Democratic party?",
  "subtitle": "Abdul El-Sayed",
  "status": "active",
  "result": null,
  "yes_price": 0.005,
  "no_price": 0.995,
  "yes_bid": 0,
  "yes_ask": 0.01,
  "no_bid": 0.99,
  "no_ask": 1,
  "last_price": 0.01,
  "volume": 4860938.34,
  "volume_24h": 597091.38,
  "volume_24h_source": "market",
  "open_interest": 3305465.44,
  "open_interest_source": "market",
  "liquidity": null,
  "close_time": "2028-11-07T15:00:00Z",
  "url": "https://kalshi.com/markets/kxpresnomd",
  "fetched_at": "2026-10-19T12:06:51.746112+00:00",
  "volume_rank": 1,
  "rank": 2
}

Common uses

• Track odds and volume across two prediction markets in one table.
• Feed an AI agent or dashboard with a clean market snapshot.
• Compare pricing on the same event when both venues list it.
• Build a dataset of resolved markets for calibration research.

Pricing

Pay per event: $0.005 per market row written to the dataset. A default run returns up to 100 markets per venue (200 rows) and costs about $1.00. The run page shows the maximum charge before you start, and the actor stops writing rows when your budget is reached.

The price is charged only for rows actually written. If a venue fails or a filter removes everything, you pay for nothing.

Notes and limitations

• This actor is read-only. It does not place, cancel or settle trades.
• Kalshi prices are returned as probabilities between 0 and 1. Legacy cent fields are converted automatically.
• Polymarket can return a legal or geo block (HTTP 451) from some networks. When that happens the actor records the HTTP status in VENUE_STATUS and returns Kalshi data. It does not route around the block with proxies by default.
• The actor returns market data, not financial advice. Verify anything you trade on at the source.
• Not affiliated with Kalshi or Polymarket.

Support

Open an issue on the actor page and include the run ID plus the VENUE_STATUS value.