Prediction Market API: Build Your Own Trading Bot

Algorithmic trading has transcended institutional finance. The Polymarket API grants engineers direct access to the globe's premier prediction market ecosystem. Whether your goal is automating a straightforward portfolio rebalancing approach or engineering a complex market-making engine, this resource walks you through the essentials needed to launch your project.

API Architecture Overview

Polymarket makes available two principal API layers:

• Gamma API (gamma-api.polymarket.com): Event catalogues, market listings, condition hierarchies, and past performance records. Open access, no credentials required
• CLOB API (clob.polymarket.com): Order submission, removal, portfolio tracking, and live order book snapshots. Demands EIP-712 authorisation tokens

Authentication

CLOB API security operates across two tiers:

1. L1 Authentication (EIP-712): Sign a structured message using your Ethereum account's private key to generate API tokens (apiKey, secret, passphrase)
2. L2 Authentication (HMAC-SHA256): Cryptographically sign every request using your generated tokens. The signature encodes the request timestamp, HTTP verb, endpoint path, and 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 supplies the complete dataset required for market intelligence:

// 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 execution directives:

• GTC (Good-Till-Cancelled): Remains active in the order book until executed or withdrawn
• GTD (Good-Till-Date): Automatically expires after a designated moment
• FOK (Fill-Or-Kill): Executes in full or not at all
• IOC (Immediate-Or-Cancel): Executes available volume, discards unmatched remainder

WebSocket Streaming

To obtain live market signals, establish a connection to the CLOB WebSocket gateway:

// 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 approach would:

1. Track price movements across your chosen markets through WebSocket feeds
2. Compute a moving average spanning the preceding 24-hour window
3. Initiate purchases when quoted prices fall 10%+ beneath the calculated average
4. Exit positions once prices stabilise near the average level
5. Employ Kelly criterion methodology for stake determination

Rate Limits and Best Practices

• CLOB API: 100 requests per 10 seconds per API key
• Implement exponential backoff handling when receiving 429 status codes
• Favour WebSocket connections for live market data rather than repeated polling cycles
• Store your private key within environment configuration, never hardcoded
• Validate strategies using minimal capital before expanding exposure

PolyGram users can engage with all these markets via a streamlined dashboard — API integration is entirely optional. Start trading on PolyGram →