Polymarket

Installation

pip install py-clob-client

Authentication

CRITICAL: Magic.Link Users (Google/Email login)

Magic.Link creates TWO wallets:

• Signer: Signs transactions (has private key - export from wallet.magic.link)
• Proxy: Holds funds (shown in Polymarket UI - smart contract, no key)

from py_clob_client.client import ClobClient

client = ClobClient(
    host="https://clob.polymarket.com",
    key=SIGNER_PRIVATE_KEY,      # From wallet.magic.link export
    chain_id=137,
    signature_type=1,            # MUST be 1 for Magic.Link!
    funder=PROXY_WALLET_ADDRESS  # Address from Polymarket UI
)

# Create/derive API credentials
creds = client.create_or_derive_api_creds()
client.set_api_creds(creds)

EOA Wallets (MetaMask/hardware)

client = ClobClient(
    host="https://clob.polymarket.com",
    key=PRIVATE_KEY,
    chain_id=137,
    signature_type=0  # EOA
)

Place Orders

from py_clob_client.clob_types import OrderArgs, MarketOrderArgs, OrderType
from py_clob_client.order_builder.constants import BUY, SELL

# Limit order
order = client.create_order(OrderArgs(
    price=0.50,
    size=100,  # MINIMUM 5 shares!
    side=BUY,
    token_id="<token-id>"
))
client.post_order(order)

# Market order (FOK = Fill-or-Kill)
market_order = client.create_market_order(MarketOrderArgs(
    token_id="<token-id>",
    amount=100.0,  # USDC for BUY, shares for SELL
    side=BUY
))
client.post_order(market_order, OrderType.FOK)

# Cancel
client.cancel(order_id)
client.cancel_all()

Get Market Data

# Order book
book = client.get_order_book(token_id)
best_bid = float(book.bids[0].price)  # Prices are strings!
best_ask = float(book.asks[0].price)

# Midpoint
mid = client.get_midpoint(token_id)

Critical Gotchas

1. JSON String Fields in Gamma API

outcomePrices and clobTokenIds are JSON strings, not arrays:

import json

market = gamma_response
# WRONG: market["clobTokenIds"][0]
# RIGHT:
clob_ids = json.loads(market["clobTokenIds"])
yes_token = clob_ids[0]
no_token = clob_ids[1]

2. Minimum Order Size

Minimum is 5 shares, not $5 USD:

• At $0.10 price: 5 shares = $0.50 minimum
• At $0.90 price: 5 shares = $4.50 minimum

3. slug vs eventSlug for URLs

# WRONG - 404 error
f"https://polymarket.com/event/{position['slug']}"

# RIGHT
f"https://polymarket.com/event/{position['eventSlug']}"

4. /trades Endpoint Does NOT Filter by Wallet

# DOES NOT WORK - returns ALL platform trades
GET /trades?proxyWallet=0x...

# USE THIS for user-specific trades:
GET /activity?user=0x...&limit=100

5. Gamma API Prices are Normalized

outcomePrices always sum to $1.00 - can't find arbitrage here. Use CLOB orderbook for real bid/ask spreads.

6. Orderbook Prices are Strings

# WRONG
best_bid = book.bids[0].price + 0.01

# RIGHT
best_bid = float(book.bids[0].price) + 0.01

Common Patterns

Fetch User Positions

import httpx

async def get_positions(wallet: str):
    url = "https://data-api.polymarket.com/positions"
    async with httpx.AsyncClient() as client:
        resp = await client.get(url, params={"user": wallet})
        return resp.json()

Fetch Whale Trades (Activity Endpoint)

async def get_whale_trades(wallet: str, limit: int = 100):
    url = "https://data-api.polymarket.com/activity"
    async with httpx.AsyncClient() as client:
        resp = await client.get(url, params={
            "user": wallet,
            "limit": limit
        })
        return resp.json()

Get Top Traders (Leaderboard)

async def get_leaderboard(period: str = "week"):
    url = "https://data-api.polymarket.com/v1/leaderboard"
    async with httpx.AsyncClient() as client:
        resp = await client.get(url, params={
            "timePeriod": period,
            "orderBy": "PNL",
            "limit": 20
        })
        return resp.json()

Reference Files

For detailed documentation, see:

• references/api-reference.md - Complete API endpoints (Gamma, CLOB, Data APIs)
• references/sdks.md - SDK patterns (Python, TypeScript, Rust)
• references/websocket.md - Real-time streaming patterns
• references/trading.md - Order types, arbitrage detection, market making

Environment Variables

POLYMARKET_PRIVATE_KEY=0x...     # Signer key
POLY_FUNDER_ADDRESS=0x...        # Proxy wallet (Magic.Link users)
POLY_SIGNATURE_TYPE=1            # 0=EOA, 1=PolyProxy
POLY_API_KEY=...                 # After credential creation
POLY_SECRET=...
POLY_PASSPHRASE=...

Error Handling