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Order Book

Last updated: Mar 11, 2026

Synthetix perpetual futures markets use a central limit order book (CLOB). If you have traded on a centralized exchange before, the structure will feel familiar.

An order book is a live list of:

  • Buy orders (bids) — traders willing to buy at a given price
  • Sell orders (asks) — traders willing to sell at a given price

When a buy order and a sell order are compatible, they match and execute.

Price levels and tick size

Orders can only be placed at prices that align with the market's tick size.

  • Tick size = the smallest allowed price increment
  • Example: if tick size is 0.5, valid prices are 100.0, 100.5, 101.0, and so on

This keeps the order book organized into clean price levels.

Tick size varies by market. You can find current market settings in Markets.

Order size and lot size

Order sizes must align with the market's lot size.

  • Lot size = the smallest allowed size increment
  • Example: if the lot size is 0.001 BTC, valid sizes are 0.001, 0.002, 0.003 BTC, and so on

Lot size also varies by market. See Markets for current limits and parameters.

How matching works

Orders are matched using price-time priority, which is the standard model for most order-book exchanges.

On the trading page, you can view live bids, asks, and the spread directly in the order book panel.

Price priority

Better prices fill first.

  • For buy orders, a higher price is better
  • For sell orders, a lower price is better

For example:

  • A bid at 101 fills before a bid at 100
  • An ask at 99 fills before an ask at 100

Time priority

If multiple orders are placed at the same price level, the order submitted first is first in line.

For example, if two buy orders are both placed at 100, the earlier order fills first.

Maker vs taker

When a trade happens, one side typically provides liquidity and the other removes it:

  • Maker — your order rests on the order book and provides liquidity
  • Taker — your order fills immediately against existing liquidity

This distinction matters because maker and taker trades can be charged different fees. See Fees.

Partial fills

A single order can be:

  • Fully filled — the entire order executes
  • Partially filled — some of the order executes and the remainder may either stay on the book or be canceled, depending on the order type

For resting limit orders, any unfilled remainder stays on the book and keeps its original time priority at that price level.

For order types such as IOC, any unfilled remainder is canceled instead of resting on the book.

Quick glossary

  • Bid — a buy order resting on the book
  • Ask — a sell order resting on the book
  • Spread — the difference between the best bid and best ask
  • Tick size — the minimum allowed price increment
  • Lot size — the minimum allowed size increment
  • Price-time priority — matching by best price first, then earliest order

See also