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Arbiter

One API to access every prediction market. Arbiter aggregates Polymarket and Kalshi into a single interface with normalized data, historical archives, and real-time streaming. 
curl https://api.arbiterapi.com/v1/markets?limit=3 \
  -H "X-API-Key: YOUR_API_KEY"

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Why use Arbiter instead of the exchange APIs directly?

Unified access — one API key, one data format, one SDK instead of integrating with each exchange separately. All prices normalized to 0-1 probability, all timestamps in Unix ms. Historical data — we store every trade, every orderbook snapshot, and compute OHLCV candles at every interval. Polymarket and Kalshi don’t provide deep historical access through their public APIs. With Arbiter, you can query months of trade history, historical orderbook state, and candlestick data for any market. Cross-platform intelligence — find the same event listed on both Polymarket and Kalshi. Track wallet positions and PnL across platforms. Compare pricing between exchanges.

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What you get

  • Markets and events — search, filter, and browse across all platforms
  • Historical trades — full trade history per market or per wallet
  • Historical orderbooks — queryable snapshots over time
  • OHLCV candles — 1-minute to 1-day intervals
  • Prices — current or at any point in time via at_time
  • Wallet analytics — positions, PnL, and on-chain activity for any address
  • Cross-platform matching — same event on Polymarket and Kalshi
  • WebSocket — real-time trades, prices, and orderbook updates
  • TypeScript and Python SDKs

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Quick example

import { ArbiterClient } from '@arbiter/sdk';

const arbiter = new ArbiterClient({ apiKey: 'YOUR_API_KEY' });

const markets = await arbiter.markets.list({ limit: 10 });
const pnl = await arbiter.wallets.pnl('0xd91c...');
const matches = await arbiter.matching.list();

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Next

Quickstart

First request in 2 minutes.

API Reference

Full endpoint docs.