Prediction Market API: Build Your Own Trading Bot

Algorithmic trading extends well beyond institutional finance desks. The Polymarket API grants programmers unrestricted entry to the globe's premier prediction marketplace. Whether your goal is to streamline a straightforward rebalancing approach or construct an advanced market-making system, this resource walks you through every step required to begin.

API Architecture Overview

Polymarket offers two principal APIs:

• Gamma API (gamma-api.polymarket.com): Event information, market listings, condition details, and past performance records. Openly accessible, authentication not required
• CLOB API (clob.polymarket.com): Order submission, removal, portfolio oversight, and live order book information. Demands EIP-712 derived API credentials

Authentication

CLOB API security operates across two tiers:

1. L1 Authentication (EIP-712): Sign a structured-data payload using your Ethereum private key to obtain API credentials (apiKey, secret, passphrase)
2. L2 Authentication (HMAC-SHA256): Sign every API call with your derived credentials. The signature encompasses the timestamp, HTTP method, endpoint path, and request payload

Example credential derivation (JavaScript):

import { ethers } from "ethers";
const wallet = new ethers.Wallet(PRIVATE_KEY);
const domain = { name: "ClobAuthDomain", ... };
const types = { ClobAuth: [{ name: "address", type: "address" }, ...] };
const signature = await wallet.signTypedData(domain, types, value);
// POST to /auth/derive-api-key with the signature

Fetching Market Data

The Gamma API furnishes all the market information your bot requires:

// List active events
GET https://gamma-api.polymarket.com/events?active=true&limit=100

// Get specific market details
GET https://gamma-api.polymarket.com/markets/{conditionId}

// Historical price data
GET https://gamma-api.polymarket.com/markets/{conditionId}/prices

Placing Orders

The CLOB API accommodates market orders, limit orders, and varied time-in-force configurations:

• GTC (Good-Till-Cancelled): Remains active in the order book until executed or withdrawn
• GTD (Good-Till-Date): Terminates at a designated moment
• FOK (Fill-Or-Kill): Must execute in full or be rejected entirely
• IOC (Immediate-Or-Cancel): Executes available quantity, discards the remainder

WebSocket Streaming

To obtain instantaneous market information, establish a connection to the CLOB WebSocket service:

// Subscribe to order book updates
ws.send(JSON.stringify({
  type: "subscribe",
  channel: "market",
  assets_id: TOKEN_ID
}));

Building a Simple Strategy

A straightforward mean-reversion system could operate as follows:

1. Observe price movements across chosen markets through WebSocket feeds
2. Determine a moving average across the preceding 24-hour window
3. Initiate purchases when price falls 10%+ beneath the moving average
4. Close positions when price recovers to the moving average level
5. Apply Kelly criterion methodology for optimal position sizing

Rate Limits and Best Practices

• CLOB API: 100 requests per 10 seconds per API key
• Consistently apply exponential backoff when receiving 429 responses
• Favour WebSocket connections for live data rather than repeated polling
• Store your private key in environment variables, never embed it directly
• Validate strategies on modest holdings before expanding exposure

PolyGram users gain access to all these markets via a streamlined dashboard — no coding or API integration needed. Start trading on PolyGram →