Free Tool: Scan 10,000+ Prediction Markets for Anomalies (Python, No API Key)

#python #productivity #opensource #beginners

Prediction markets like Polymarket have exploded in 2024-2026, processing billions in volume. But with 10,000+ active markets, nobody can manually track all of them.

I built an open-source Python scanner that does it automatically — no API key needed, completely free.

What It Detects

1. Exclusive Outcome Mispricings

When an event has mutually exclusive outcomes ("Who will win the election?"), the YES prices should sum to ~100%. When they don't, there's a potential arbitrage.

# Example: 4 candidates in an election
# Candidate A: 45% + B: 30% + C: 15% + D: 5% = 95%
# That missing 5% is potential profit
total_yes = sum(m.yes_price for m in markets)
deviation = abs(total_yes - 1.0)
if deviation > 0.03:  # More than 3% deviation
    print(f"Mispricing found: {deviation:.1%}")

2. Ladder Contradictions

Threshold markets ("Will BTC hit $X?") create logical chains. If "BTC > $80K" is priced at 60%, then "BTC > $90K" must be ≤ 60%. When this is violated, something is wrong.

# Detect when a higher threshold is priced above a lower one
for i in range(len(sorted_markets) - 1):
    lower, higher = sorted_markets[i], sorted_markets[i + 1]
    if lower["market"].yes_price < higher["market"].yes_price:
        print(f"Contradiction: {lower} vs {higher}")

How It Works

The scanner uses Polymarket's public Gamma API (gamma-api.polymarket.com):

Fetch all active events with pagination
Parse market data (prices, liquidity, volume)
Scan for logical inconsistencies
Filter by confidence and liquidity

No authentication needed. The API is completely open.

Quick Start

git clone https://github.com/vesper-astrena/polymarket-scanner
cd polymarket-scanner
pip install requests
python polymarket_scanner.py

Output:

=== Polymarket Scanner (Free Edition) ===
Fetching events...
  500 events, 8000 markets

Scanning exclusive outcomes...
  3 high-confidence opportunities

Scanning ladder contradictions...
  12 contradictions found

Why This Matters

Prediction markets are supposed to be efficient, but:

New markets often have thin liquidity and wide spreads
Threshold ladders frequently have logical violations
Multi-outcome events drift as individual markets move independently

The scanner finds these edge cases automatically.

Want More?

The free version covers basic scanning. The full toolkit ($29) adds:

Cross-market logical implication analysis
Bidirectional ladder detection (HIGH + LOW)
Confidence scoring system
Scheduled 24/7 monitoring with alerts
Extensible architecture for custom strategies

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