Prediction Markets Monitor — Polymarket & Kalshi

One actor, both prediction markets. Track live odds, spot the biggest movers, catch new markets the moment they open, and maintain watchlists across Polymarket and Kalshi — normalized into a single output schema.

Both sources are official free public APIs — no API key, no account, no proxy required. Built for scheduled monitoring: run it on a cron and get fresh odds snapshots every cycle.

What it does

Mode	Output
markets	Top markets by 24h volume — unified Polymarket + Kalshi, with optional keyword, volume, liquidity, and closing-date filters
movers	Markets whose odds moved ≥ your threshold in the last 24h — catch breaking sentiment shifts before they're news
new	Recently created markets sorted by creation time — be first to new listings
watch	Snapshot your own watchlist of market IDs — the primitive for cron-driven odds tracking and alerting

Why this one

• Unified schema — Polymarket and Kalshi rows share identical fields (platform, question, topOutcome, topPrice, volume24hUsd, liquidityUsd, endDate, price changes). Diff them in one query.
• Movers detection built in — Polymarket's oneDayPriceChange/oneHourPriceChange fields plus Kalshi's previous_price give you odds-shift alerts without storing baselines.
• Election-season ready — midterm and presidential markets are where prediction-market volume concentrates; this actor is built for exactly that scheduled-monitoring workload.
• Zero credentials — both APIs are keyless. No rate-limit roulette, no token management.

Input examples

Top active markets on both platforms:

{ "mode": "markets", "platform": "all", "maxResults": 50 }

Election keyword, markets closing within 90 days:

{
  "mode": "markets",
  "query": "election",
  "closeWithinDays": 90,
  "maxResults": 30
}

Odds movers ≥3% with at least $10k volume:

{ "mode": "movers", "minOddsMove": 3, "minVolumeUsd": 10000 }

Watchlist snapshot (mix Polymarket slugs/conditionIds and Kalshi tickers):

{
  "mode": "watch",
  "watchlist": [
    "polymarket:fed-decision-in-october",
    "kalshi:KXPRES-28",
    "nfl-pit-cle-2026-10-02"
  ]
}

Watchlist items accept platform: prefixes (polymarket:/kalshi:), bare Kalshi tickers (KX... auto-detected), Polymarket slugs, numeric market IDs, or 0x condition IDs.

Example output

{
  "recordType": "market",
  "platform": "polymarket",
  "id": "0x8a9f8be5...",
  "slug": "nfl-pit-cle-2026-10-02",
  "question": "Steelers vs. Browns",
  "outcomes": ["Steelers", "Browns"],
  "outcomePrices": [0.135, 0.865],
  "topOutcome": "Browns",
  "topPrice": 0.865,
  "priceChange1h": -0.5,
  "priceChange24h": -44.0,
  "volumeUsd": 12500000,
  "volume24hUsd": 3376472,
  "liquidityUsd": 412000,
  "endDate": "2026-10-02T20:00:00Z",
  "active": true,
  "url": "https://polymarket.com/event/nfl-pit-cle-2026-10-02"
}

priceChange* fields are percentage points (e.g. -44 = the leading outcome dropped 44 points). Kalshi rows carry ticker as id, event_ticker as slug, and Yes-side bid/ask.

Pricing

$1 per 1,000 results ($0.001 per dataset row). A 50-market hourly watchlist costs ~$1.20/month.

Use cases

• Election odds tracking — scheduled watch runs give you a time series of political market odds.
• News arbitrage — movers catches markets reacting before mainstream coverage.
• New-market discovery — new surfaces fresh listings for first-mover trading or research.
• Cross-platform research — unified output makes Polymarket↔Kalshi comparisons a single dataset query.

Notes & limitations

• Polymarket data comes from the public gamma API; Kalshi from the public elections API — both keyless but subject to the platforms' own rate limits (built-in retry/backoff handles 429s).
• Kalshi keyword search scans the top open events server-side; for precise Kalshi lookups use watch with exact tickers.
• Brand-new markets may have no prices yet (null price fields until first trade).

FAQ

Does Prediction Markets Monitor need a login or API key? No — every row comes from public endpoints. Provide a proxy only if your network is heavily rate-limited.

How do I monitor on a schedule? Attach the actor to an Apify Schedule (daily/weekly) and use the watch/monitor mode if present — each run emits a fresh, diff-able dataset.

What does each row contain? See the output fields table above; every row carries a scrapedAt timestamp so datasets can be deduped across runs.

Is it legal to scrape this data? The actor only accesses publicly available data — the same pages/APIs a browser sees. Scraping public data for research, monitoring, and analysis is common practice, but platform Terms of Service and the rules in your jurisdiction still apply to how you use it. Consult legal counsel for your specific case.

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