Polymarket API & Python Trading Bot Tutorial: Fetching Live Gamma Odds & Automating 0%-Fee CLOB Orders

Polymarket provides two open developer APIs with zero subscription fees:
1. Gamma Markets REST API (https://gamma-api.polymarket.com/markets): Public read-only endpoint for market metadata, 24h volume, liquidity depth, resolution rules, and current Yes/No prices (used by P.DAY's JEV Pick 99.4% engine).
2. CLOB Orderbook API & WebSocket (https://clob.polymarket.com): Millisecond L2 orderbook feed and authenticated endpoint for resting/canceling limit orders via the official Python SDK py-clob-client.

Install the official SDK with pip install py-clob-client requests and query active markets immediately:

import requests
# Fetch top 20 active Polymarket contracts sorted by volume
mkts = requests.get('https://gamma-api.polymarket.com/markets?active=true&closed=false&limit=20').json()
for m in mkts[:5]:
    print(m['question'], '| Vol:', m.get('volumeNum'), '| Prices:', m.get('outcomePrices'))

To place automated 0%-fee limit orders, initialize ClobClient("https://clob.polymarket.com", key=YOUR_PRIVATE_KEY, chain_id=137) and derive L2 API credentials to quote and cancel orders gas-free.

Strategy A (Multi-Outcome Sum Arbitrage / NegRisk Rebalancing): In multi-candidate markets (e.g., championship or election primaries), the sum of all 'Yes' probabilities should equal 100%. When retail order flow pushes the sum below 97¢ or above 103¢, bots arbitrage the basket back to parity.
Strategy B (Two-Sided Spread Capture + Liquidity Rewards): Quote resting bids and asks around the fair value computed by our Quant Calibration Model to earn both bid-ask spread and daily USDC maker rewards.