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

In this guide

Available Data Endpoints
Python Quickstart
Use Cases
FAQ

Developers seeking to leverage prediction market intelligence for research, journalism, and quantitative modelling now have access to comprehensive APIs. The Polymarket platform (available through PolyGram) offers extensive datasets and technical infrastructure for those building applications atop the globe's most active prediction market ecosystem.

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: Monitor probability shifts across prediction markets throughout event lifecycles
News tools: Identify markets experiencing significant movement following major announcements
Aggregators: Benchmark odds between Polymarket, Kalshi, and Metaculus to spot arbitrage opportunities
Alert systems: Trigger notifications whenever market valuations shift past predetermined boundaries
Academic research: Utilise resolved market outcomes for evaluating forecast performance and prediction accuracy

FAQ

Is the Polymarket API free to use?: Yes — market data via the Gamma API is available at no cost, subject to standard rate restrictions (roughly 100 requests per minute without authentication). Submitting orders through the CLOB requires an active wallet, though retrieving data remains complimentary.
Is there a Python library for Polymarket?: Multiple community-developed Python packages are available on GitHub. Look for "polymarket-py" to find the most actively maintained versions.