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The orderbook is a public endpoint — no authentication required. You can read prices and liquidity using the SDK or REST API directly. 
import { ClobClient } from "@polymarket/clob-client";

const client = new ClobClient("https://clob.polymarket.com", 137);

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Get the Orderbook

Fetch the full orderbook for a token, including all resting bid and ask levels: 
const book = await client.getOrderBook("TOKEN_ID");

console.log("Best bid:", book.bids[0]);
console.log("Best ask:", book.asks[0]);
console.log("Tick size:", book.tick_size);

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Response

{
  "market": "0xbd31dc8a...",
  "asset_id": "52114319501245...",
  "timestamp": "2023-10-21T08:00:00Z",
  "bids": [
    { "price": "0.48", "size": "1000" },
    { "price": "0.47", "size": "2500" }
  ],
  "asks": [
    { "price": "0.52", "size": "800" },
    { "price": "0.53", "size": "1500" }
  ],
  "min_order_size": "5",
  "tick_size": "0.01",
  "neg_risk": false,
  "hash": "0xabc123..."
}
FieldDescription
marketCondition ID of the market
asset_idToken ID
bidsBuy orders sorted by price (highest first)
asksSell orders sorted by price (lowest first)
tick_sizeMinimum price increment for this market
min_order_sizeMinimum order size for this market
neg_riskWhether this is a multi-outcome (neg risk) market
hashHash of the orderbook state — use to detect changes

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Prices

Get the best available price for buying or selling a token: 
const buyPrice = await client.getPrice("TOKEN_ID", "BUY");
console.log("Best ask:", buyPrice.price); // Price you'd pay to buy

const sellPrice = await client.getPrice("TOKEN_ID", "SELL");
console.log("Best bid:", sellPrice.price); // Price you'd receive to sell

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Midpoints

The midpoint is the average of the best bid and best ask. This is the price displayed on Polymarket as the market’s implied probability. 
const midpoint = await client.getMidpoint("TOKEN_ID");
console.log("Midpoint:", midpoint.mid); // e.g., "0.50"
If the bid-ask spread is wider than $0.10, Polymarket displays the last traded price instead of the midpoint.

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Spreads

The spread is the difference between the best ask and the best bid. Tighter spreads indicate more liquid markets. 
const spread = await client.getSpread("TOKEN_ID");
console.log("Spread:", spread.spread); // e.g., "0.04"

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Price History

Fetch historical price data for a token over various time intervals: 
import { PriceHistoryInterval } from "@polymarket/clob-client";

const history = await client.getPricesHistory({
  market: "TOKEN_ID", // Note: this param is named "market" but takes a token ID
  interval: PriceHistoryInterval.ONE_DAY,
  fidelity: 60, // Data points every 60 minutes
});

// Each entry: { t: timestamp, p: price }
history.forEach((point) => {
  console.log(`${new Date(point.t * 1000).toISOString()}: ${point.p}`);
});
IntervalDescription
1hLast hour
6hLast 6 hours
1dLast day
1wLast week
1mLast month
maxAll available data
interval is relative to the current time. Use startTs / endTs for absolute time ranges. They are mutually exclusive — don’t combine them.

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Estimate Fill Price

Calculate the effective price you’d pay for a market order of a given size, accounting for orderbook depth: 
import { Side, OrderType } from "@polymarket/clob-client";

// What price would I pay to buy $500 worth?
const price = await client.calculateMarketPrice(
  "TOKEN_ID",
  Side.BUY,
  500, // dollar amount
  OrderType.FOK,
);

console.log("Estimated fill price:", price);
This walks the orderbook to estimate slippage. Useful for sizing market orders before submitting them.

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Batch Requests

All orderbook queries have batch variants for fetching data across multiple tokens in a single request (up to 500 tokens):
SingleBatchREST
getOrderBook()getOrderBooks()POST /books
getPrice()getPrices()POST /prices
getMidpoint()getMidpoints()POST /midpoints
getSpread()getSpreads()POST /spreads
getLastTradePrice()getLastTradesPrices()—
BookParams for batch orderbook requests accepts a token_id and an optional side parameter to filter by bid or ask side.
import { Side } from "@polymarket/clob-client";

// Fetch prices for multiple tokens
const prices = await client.getPrices([
  { token_id: "TOKEN_A", side: Side.BUY },
  { token_id: "TOKEN_B", side: Side.BUY },
]);
// Returns: { "TOKEN_A": { "BUY": "0.52" }, "TOKEN_B": { "BUY": "0.74" } }

​
Last Trade Price

Get the price and side of the most recent trade for a token: 
const lastTrade = await client.getLastTradePrice("TOKEN_ID");
console.log(lastTrade.price, lastTrade.side);
// e.g., "0.52", "BUY"

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Real-Time Updates

For live orderbook data, use the WebSocket API instead of polling. The market channel streams orderbook changes, price updates, and trade events in real time.

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Connecting

const ws = new WebSocket(
  "wss://ws-subscriptions-clob.polymarket.com/ws/market",
);

ws.onopen = () => {
  ws.send(
    JSON.stringify({
      type: "market",
      assets_ids: ["TOKEN_ID"],
      custom_feature_enabled: true, // enables best_bid_ask, new_market, market_resolved events
    }),
  );
};

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);
  switch (data.event_type) {
    case "book": // full orderbook snapshot
    case "price_change": // individual price level update
    case "last_trade_price": // new trade executed
    case "tick_size_change": // market tick size changed
    case "best_bid_ask": // top-of-book update (requires custom_feature_enabled)
    case "new_market": // new market created (requires custom_feature_enabled)
    case "market_resolved": // market resolved (requires custom_feature_enabled)
  }
};

​
Dynamic Subscribe and Unsubscribe

After connecting, you can change your subscriptions without reconnecting: 
// Subscribe to additional tokens
ws.send(
  JSON.stringify({
    assets_ids: ["NEW_TOKEN_ID"],
    operation: "subscribe",
  }),
);

// Unsubscribe from tokens
ws.send(
  JSON.stringify({
    assets_ids: ["OLD_TOKEN_ID"],
    operation: "unsubscribe",
  }),
);

​
Event Types

EventTriggerKey Fields
bookOn subscribe + when a trade affects the bookbids[], asks[], hash, timestamp
price_changeNew order placed or order cancelledprice_changes[] with price, size, side, best_bid, best_ask
last_trade_priceTrade executedprice, side, size, fee_rate_bps
tick_size_changePrice hits >0.96 or < 0.04old_tick_size, new_tick_size
best_bid_askTop-of-book changesbest_bid, best_ask, spread
new_marketMarket createdquestion, assets_ids, outcomes
market_resolvedMarket resolvedwinning_asset_id, winning_outcome
best_bid_ask, new_market, and market_resolved require custom_feature_enabled: true in your subscription message.
The tick_size_change event is critical for trading bots. If the tick size changes and you continue using the old tick size, your orders will be rejected.

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Next Steps

Place Orders

Create and submit orders using the orderbook data

Fetching Markets

Find token IDs for markets you want to trade