CLOB API

Polymarket CLOB API is the HTTP surface for the platform's Central Limit Order Book — it serves order-book data, historical prices, midpoint and tick-size information, and exposes authenticated endpoints for placing and cancelling orders. Reads are publicly accessible; trading endpoints require an API key plus an HMAC signature.

In context

You encounter the CLOB API when you need granular market data or programmatic access to Polymarket's matching engine. Use it to fetch the live order book, request midpoint prices, or automate order placement and cancellation. Public (read) endpoints let third-party tools and market-data consumers pull best bid/ask, price history, and order-book snapshots. For sending orders, the API mandates an API key and HMAC authentication and integrates with Polymarket's Builder program for attribution and optional builder-fee routing.

The Market WebSocket complements the CLOB API for real-time updates: subscribe to live book changes, price_change, best_bid_ask, last_trade_price and tick_size_change events. Note the WebSocket's 10-second PING and the 500-instrument-per-connection limit when designing listeners.

See also

• /glossary/gamma-api
• /glossary/data-api
• /glossary/clob