MCPInstall

polymarket-api

Deep integration guide for Polymarket's CLOB API, Gamma API, and on-chain data. Use when building trading functionality, fetching market data, or implementing order execution.

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Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/agentmc15/polymarket-trader --skill polymarket-api
  1. 01

    Install

    Run the command in your project. The CLI asks which agents to install for.

  2. 02

    Describe the task

    Ask your agent for something this skill covers. It loads polymarket-api automatically when relevant.

  3. 03

    Review the result

    The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

Polymarket API Integration Skill

Overview

This skill provides comprehensive guidance for integrating with Polymarket's APIs and smart contracts.

API Endpoints

CLOB API (Central Limit Order Book)

Base URL: https://clob.polymarket.com

Authentication Levels

  • Level 0 (Public): Market data, orderbooks, prices
  • Level 1 (Signer): Create/derive API keys
  • Level 2 (Authenticated): Trading, orders, positions

Key Endpoints

GET  /markets              # List all markets
GET  /markets/{condition_id}  # Get specific market (condition_id is the
                               # MARKET key; token_id is the per-outcome
                               # BOOK key used by /price, /midpoint, /book
                               # below — the two are not interchangeable)
GET  /price?token_id=X     # Get current price
GET  /midpoint?token_id=X  # Get midpoint price
GET  /book?token_id=X      # Get orderbook
GET  /trades               # Get user trades
POST /order                # Place order
DELETE /order/{id}         # Cancel order
GET  /positions            # Get positions

Gamma API (Market Metadata)

Base URL: https://gamma-api.polymarket.com

GET /events              # List events
GET /events/{slug}       # Get event details
GET /markets             # List markets
GET /markets/{id}        # Get market details

Python Implementation Patterns

Initialize Client

from py_clob_client.client import ClobClient
from py_clob_client.clob_types import OrderArgs, OrderType
import os

class PolymarketService:
    def __init__(self):
        self.client = ClobClient(
            host="https://clob.polymarket.com",
            key=os.getenv("POLYMARKET_PRIVATE_KEY"),
            chain_id=137,
            signature_type=1,
            funder=os.getenv("POLYMARKET_FUNDER_ADDRESS")
        )
        self.client.set_api_creds(
            self.client.create_or_derive_api_creds()
        )
    
    async def get_market_data(self, token_id: str) -> dict:
        """Fetch comprehensive market data."""
        return {
            "price": self.client.get_price(token_id, "BUY"),
            "midpoint": self.client.get_midpoint(token_id),
            "book": self.client.get_order_book(token_id),
            "spread": self.client.get_spread(token_id),
        }
    
    async def place_order(
        self,
        token_id: str,
        side: str,
        price: float,
        size: float,
        order_type: str = "GTC"
    ) -> dict:
        """Place a limit order."""
        order = self.client.create_order(
            OrderArgs(
                token_id=token_id,
                price=price,
                size=size,
                side=side,
            )
        )
        return self.client.post_order(order, order_type)

WebSocket Subscription

import asyncio
import websockets
import json

async def subscribe_market_updates(token_ids: list[str]):
    """Subscribe to real-time market updates."""
    uri = "wss://ws-subscriptions-clob.polymarket.com/ws/market"
    
    async with websockets.connect(uri) as ws:
        await ws.send(json.dumps({
            "type": "subscribe",
            "markets": token_ids
        }))
        
        async for message in ws:
            data = json.loads(message)
            yield data

Gamma API Client

import httpx

class GammaClient:
    BASE_URL = "https://gamma-api.polymarket.com"
    
    def __init__(self):
        self.client = httpx.AsyncClient(base_url=self.BASE_URL)
    
    async def get_active_markets(self) -> list[dict]:
        """Fetch all active markets."""
        response = await self.client.get("/markets", params={"active": True})
        return response.json()
    
    async def get_event(self, slug: str) -> dict:
        """Fetch event with all markets."""
        response = await self.client.get(f"/events/{slug}")
        return response.json()

Order Types

  • GTC (Good Till Cancelled): Stays until filled or cancelled
  • GTD (Good Till Date): Expires at specified time
  • FOK (Fill or Kill): Must fill entirely or cancel
  • IOC (Immediate or Cancel): Fill what's available, cancel rest

Fee Model

Polymarket's taker-only formula (docs.polymarket.com/trading/fees, fetched 2026-09-04):

fee = C × rate × p × (1 − p)

Where:

  • C = contract count ($1 per contract at resolution)
  • rate = taker fee rate (category-dependent, makers never pay)
  • p = fill price, a probability in [0, 1]
  • (1 − p) = the fee term; maximized at p=0.5 (coin-flip), vanishes at tails (p→0 or p→1)

Category taker rates (charged in USDC):

CategoryRate
Crypto0.07
Sports / Economics / Culture / Weather / Other0.05
Finance / Politics / Mentions / Tech0.04
Geopolitics0.00

Per-market override: The CLOB market payload may carry maker_base_fee/taker_base_fee (historical field names), which is authoritative over the category table when present. These fields are in BASIS POINTS, not a dimensionless rate — taker_base_fee=700 means 0.07, not 700. Divide by 10_000 to get the rate FeeSchedule expects (app/venues/polymarket/adapter.py does this at the two places it reads these fields) before building a FeeSchedule from the payload (source="clob_market") rather than from category_rate(). Skipping the division is a 10,000× fee error.

Maker fees: Always 0 on Polymarket CLOB; taker-only venue.

Price Calculations

def calculate_implied_probability(price: float) -> float:
    """Convert price to implied probability."""
    return price  # Prices ARE probabilities (0-1)

def calculate_cost(price: float, shares: float) -> float:
    """Calculate cost to buy shares."""
    return price * shares

def calculate_pnl(
    entry_price: float,
    current_price: float,
    shares: float,
    side: str
) -> float:
    """Calculate unrealized P&L."""
    if side == "BUY":
        return (current_price - entry_price) * shares
    return (entry_price - current_price) * shares

Error Handling

from py_clob_client.exceptions import PolymarketException

try:
    result = client.post_order(order)
except PolymarketException as e:
    if "INSUFFICIENT_BALANCE" in str(e):
        # Handle insufficient funds
        pass
    elif "INVALID_PRICE" in str(e):
        # Handle price out of range
        pass
    raise

Rate Limits

  • Public endpoints: ~100 requests/minute
  • Authenticated endpoints: ~1000 requests/minute
  • WebSocket: Varies by subscription type

Always implement exponential backoff and request queuing.

Key Contract Addresses (Polygon)

CONTRACTS = {
    "CTF_EXCHANGE": "0x4bFb41d5B3570DeFd03C39a9A4D8dE6Bd8B8982E",
    "NEG_RISK_CTF_EXCHANGE": "0xC5d563A36AE78145C45a50134d48A1215220f80a",
    "CONDITIONAL_TOKENS": "0x4D97DCd97eC945f40cF65F87097ACe5EA0476045",
    "USDC": "0x2791Bca1f2de4661ED88A30C99A7a9449Aa84174",
}

FAQ

What does the polymarket-api skill do?

Deep integration guide for Polymarket's CLOB API, Gamma API, and on-chain data. Use when building trading functionality, fetching market data, or implementing order execution.

How do I install polymarket-api?

Run npx skills add https://github.com/agentmc15/polymarket-trader --skill polymarket-api in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/polymarket-api/ (personal) or .claude/skills/polymarket-api/ (project).

Which AI agents can use polymarket-api?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is polymarket-api safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains polymarket-api?

It is published by agentmc15 in agentmc15/polymarket-trader. It has 967 recorded installs.

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