Using the Polymarket Data API: Real-Time Prediction Market Data for Developers

Prediction market data has become valuable for research, journalism, and quantitative analysis. The Polymarket ecosystem (accessible via PolyGram) exposes rich APIs for developers who want to build on top of the world's largest prediction market dataset.

Available Data Endpoints

Gamma API (Market Data)

GET https://gamma-api.polymarket.com/events
  ?limit=100&active=true&order=volume24hr
  Returns: event metadata, current prices, volume, tags

GET https://gamma-api.polymarket.com/events/{slug}
  Returns: full event with all markets, prices, descriptions

GET https://gamma-api.polymarket.com/markets/{conditionId}
  Returns: single market details, current order book price

CLOB API (Order Book)

GET https://clob.polymarket.com/book
  ?token_id={tokenId}
  Returns: full order book depth (bids/asks)

GET https://clob.polymarket.com/prices/history
  ?market={conditionId}&resolution=1h&startTs=1700000000
  Returns: hourly price history

WebSocket: wss://ws-subscriptions-clob.polymarket.com
  Subscribe to real-time price updates

Python Quickstart

import requests

# Get top prediction markets by volume
r = requests.get(
    "https://gamma-api.polymarket.com/events",
    params={"limit": 10, "active": "true", "order": "volume24hr"}
)
for event in r.json():
    market = event["markets"][0] if event.get("markets") else {}
    prices = market.get("outcomePrices", "[0.5,0.5]")
    import json; p = json.loads(prices)
    print(f"{event['title'][:50]}: YES={float(p[0]):.2%}")

Use Cases

• Research dashboards: Track prediction market probability over time for specific events
• News tools: Surface markets moving on breaking news
• Aggregators: Compare probabilities across Polymarket, Kalshi, and Metaculus
• Alert systems: Notify when a market moves beyond a threshold
• Academic research: Historical resolution data for forecasting accuracy studies

FAQ

Is the Polymarket API free to use?

Yes — market data (Gamma API) is free with rate limits (~100 req/min unauthenticated). CLOB order submission requires a funded wallet but data reads are free.

Is there a Python library for Polymarket?

Several community-maintained Python libraries exist on GitHub. Search "polymarket-py" for the most maintained options.