Open and close with post-only orders
Opening and closing with post-only orders works a two-leg position through resting orders: one leg rests and the other follows once it fills, or both legs rest at once. Maker fills improve the open and close spreads and are charged maker fees.
Live workspace
Cross-exchange spreads
Open spreads for the same coin across exchanges, with net funding and 24h volume for each pair of legs.
Funding rates
Live perpetual funding rates across exchanges, normalized to 8 hours, with the widest cross-exchange funding diff.
The two legs
The both legs are the same as in cross-exchange spread arbitrage or funding rate arbitrage. The difference is the order type: choose which legs rest post-only orders, one or both.
Entry, repricing and exit
Entry: with one leg post-only, the resting leg fills first and the other leg follows at market for the filled size. With both legs post-only, both legs rest orders at once.
Repricing and leg completion: resting orders follow the book as it moves. A lagging leg keeps waiting as a maker or, if allowed, closes the leg gap at market.
Exit: exit uses the same order types as entry.
Result and costs
Maker fills improve the open and close spreads and are charged maker fees. The cost is uncertain timing: price can move away from a resting order. Waiting delays the trade, and filling at market adds taker fees and slippage.
Key metrics
| Key metrics | |
|---|---|
| Fill rate | A post-only order fills only when the market trades into it. Slow fills keep the other leg waiting. |
| Fees and rebates | Maker and taker fees and rebates on both legs, per account. |
| Leg gap | The quantity gap between the two legs. Any gap is open directional exposure. |
| Depth and volume | Order book depth, volume and open interest set how much size each leg can take. |
Main risks
Unfilled orders: Price can move away from a resting order. Waiting delays the trade; filling at market adds taker fees and slippage.
Adverse selection: Resting orders tend to fill when price trades through them, and price often keeps moving the same way afterwards.
Leg gap: If one leg fills and the other does not, the position carries directional exposure until the gap closes.
Liquidation: Each perpetual leg holds its own margin. A sharp move can push the losing leg into liquidation while the gain sits on another venue and cannot cover it.
Venue risk: Funds sit on two venues. Either one can halt withdrawals, suffer an API outage, delist a market or fail.
See the main risks of arbitrage for a fuller account.
Data in Z Market Lab
The opportunity table in the market monitor lists both legs’ last prices, open and close spreads, volume and open interest, for judging whether resting orders will fill.
Execution in ZML Trade
Each leg’s order type is Market, Post-only or Post-only, catch up at market. Maker prices follow the book. A lagging leg set to Post-only, catch up at market can close the leg gap at market. Your own combos do not bid against each other.
Parameters covers order types and maker price. Risk controls covers the leg gap.