Reading the orderbook

One order book per series

Every series on Phasis — each unique combination of (underlying, expiry, strike, call/put) — has its own independent order book embedded directly in the market's on-chain state. Orders for different series never interact with each other; there is no shared liquidity pool across strikes or expiries.

This design means price discovery is entirely on-chain. Every resting bid and ask is a Sui object that can be inspected by anyone.

Bids and asks

Bids are ordered from highest price to lowest (best bid first). Asks are ordered from lowest price to highest (best ask first). When a new order crosses the spread — a buy order priced at or above the best ask, or a sell order priced at or below the best bid — the order book matches them and a fill occurs.

Reading depth (level 2)

The SDK exposes a getLevel2 helper to read the full depth snapshot for one side of one series:

const bookL2 = await getLevel2(client, {
  marketId,
  strike,
  isCall,
  isBid: true,  // false for the ask side
  ticks: 20,    // maximum price levels to return
});
// Returns: { bids: L2Level[], asks: L2Level[] }
// Each level: { price: number, qty: number }

• price is in USDC per contract (already human-scaled; no further division needed).
• qty is in contracts (already human-scaled).
• Bids are returned best-first (descending price).
• Asks are returned best-first (ascending price).

Mid-price

The mid-price is the arithmetic average of the best bid and best ask:

const mid = await getMidPrice(client, { marketId, strike, isCall });
// Returns: number (e.g., 0.0523 means $0.0523 per contract)

If either side of the book is empty, getMidPrice throws EEmptyOrderbook. Always guard against this in your UI — thin or newly listed series may have no bids or asks until a market maker provides liquidity.

Spread and liquidity

The bid-ask spread is ask − bid. A tight spread indicates a liquid, actively quoted series. A wide spread may reflect lower trading interest or an imminent volatility event.

As a rule of thumb:

• Spread below 1% of mid: highly liquid.
• Spread 1–5% of mid: moderate liquidity; consider using limit orders rather than market orders.
• Spread above 5%: thin book; a market order may fill at an unfavourable price.

How fills happen

When you submit a buy order at price P, the matching engine attempts to fill against all resting asks at or below P in price-time priority. Fills happen atomically within the transaction:

1. Position deltas are applied.
2. Open interest is updated.
3. Fees are accrued.
4. Margin lock is recomputed.

There is no settlement delay. Your position is updated in the same block as the fill.

Empty book handling

If no bids or asks exist for a series, the book is empty on that side. Your order will rest until another trader provides a counterparty (for GTC/POST_ONLY orders) or be immediately cancelled (for IOC/FOK). An empty book does not mean the series is invalid — it may simply be waiting for market makers.

Continue to Expiry and settlement.