Polymarket API

Polymarket is a prediction market on Polygon mainnet. Every market is a pair of YES/NO ERC-1155 tokens issued by the Conditional Token Framework (CTF), collateralized 1:1 in USDC. Off-chain CLOB matching, on-chain settlement, zero taker fees. Prices are in [0.00, 1.00] USDC; YES + NO ≈ 1.0 per market.

Before you write any API code — read the live docs first.

• Docs: https://docs.polymarket.com
• Official Python SDK: https://github.com/Polymarket/py-clob-client

Polymarket endpoints and auth flows have changed without notice. Prefer the official py-clob-client SDK over hand-rolled HTTP; it handles EIP-712 derivation, API credential management, and order signing. Only hand-roll when the SDK doesn't expose what you need.

Identifier model

You will juggle four distinct IDs — get them confused and queries silently return wrong data.

Quick Start

1. Read markets — Gamma API (no auth required)

import httpx

# CRITICAL: default sort is OLDEST-first — always override or you silently get closed markets
events = httpx.get("https://gamma-api.polymarket.com/events", params={
    "tag_id": 103040,        # category tag (e.g. weather)
    "order": "endDate",
    "ascending": "false",    # must be string "false", not bool
    "closed": "false",
}).json()

# Each event → markets[], each market has:
#   condition_id, clob_token_ids (YES/NO pair), question, outcomes, outcomePrices
for event in events:
    for mkt in event.get("markets", []):
        yes_token, no_token = mkt["clobTokenIds"]  # split the pair here
        print(mkt["question"], mkt["outcomePrices"])

Pagination: limit=100&offset=N, step by 100.

2. Order book and trading — CLOB API (EIP-712 auth)

uv pip install py-clob-client

import os
from py_clob_client.client import ClobClient

client = ClobClient(
    "https://clob.polymarket.com",
    chain_id=137,                                     # Polygon mainnet
    key=os.environ["POLYMARKET_PRIVATE_KEY"],          # wallet private key — env only, NEVER hardcode
    signature_type=2,                                  # 2 = Gnosis Safe proxy (Polymarket UI accounts)
                                                       # 0 = direct EOA you fully control
)
# Derives API key/secret/passphrase from the wallet signature — call once per session
client.set_api_creds(client.create_or_derive_api_creds())

token_id = "<yes_token_from_clob_token_ids>"
book = client.get_order_book(token_id)     # bids/asks for one outcome token
price = client.get_price(token_id, side="BUY")

signature_type=2 is for the proxy/Safe accounts the Polymarket web UI creates (the funder address is the Safe). Use signature_type=0 for a raw EOA you control directly. Read the live SDK docs — the type you choose affects how orders are signed on-chain.

Wallet env vars: POLYMARKET_PRIVATE_KEY, POLYMARKET_FUNDER. Never hardcode keys.

API surface overview

Chain: Polygon mainnet chain_id=137. Collateral: USDC.e at 0x2791Bca1f2de4661ED88A30C99A7a9449Aa84174.

WebSocket

# Connect to: wss://ws-subscriptions-clob.polymarket.com/ws/market
# Subscribe message:
{"type": "market", "assets_ids": ["<token_id>", "<token_id2>"]}

Event types: book (full snapshot on subscribe), price_change (delta updates), last_trade_price.

For user-level order/fill events, connect to /ws/user with a JWT derived from your API credentials.

On-chain settlement and redemption

Polymarket weather markets resolve via Weather Underground ("History" tab), on the metro's local clock with DST, midnight-to-midnight. This differs from Kalshi, which uses LST (no DST) and NWS CLI — see kalshi-weather-markets for the divergence.

After resolution, winning tokens must be redeemed manually on-chain:

# Call CTF contract redeemPositions() — the SDK or direct web3.py call
# Winnings are NOT auto-swept to your wallet

Disputes on the international book escalate to the UMA optimistic oracle (token-holder vote). This is a real resolution-divergence risk vs. Kalshi's CFTC-CCP settlement — factor it into any cross-venue comparison.

US geo / KYC constraint

US persons are blocked from Polymarket. API calls from a US IP typically require a SOCKS5 proxy from an allowed jurisdiction (use a USE_PROXY env flag pattern; never hardcode the proxy address). This constraint — combined with on-chain capital lockup and USDC/USD friction — is why most Kalshi/Polymarket arbitrage is not executable at retail scale.

Cross-references

• For strategy, sizing, and backtesting that apply across venues: prediction-market-strategy
• For the Kalshi counterpart (RSA-PSS auth, REST host, tickers, order schema): kalshi-api
• For weather settlement specifics (WU local-clock+DST vs Kalshi LST, KLGA vs KNYC station): kalshi-weather-markets

Files

References

• references/clob-and-gamma-apis.md — Full API surface, all endpoints, EIP-712 auth detail, pagination, order schema, trading-parameter defaults
• references/settlement-and-ops.md — WU/UMA resolution, redeemPositions, truth-source priority (IEM > WU > Open-Meteo), known-bad dates, geo/KYC, host-segregation, two-exchange architecture notes