Glossary
What is a post-only order?
Also called: post only order, maker-only order, ALO, add liquidity only
Updated Ninja Terminal team
Definition
A post-only order is a limit order that must be added to the order book and can never execute immediately as a taker. If the order would match a resting order on arrival, the exchange rejects or cancels it instead of filling it. Traders use post-only to guarantee maker fees and avoid paying the spread.
A normal limit order priced at or through the opposite best price fills at once and pays the taker fee. Post-only blocks that outcome.
Why use it?
- To guarantee the maker side of maker and taker fees.
- To avoid crossing the bid-ask spread by mistake when the market moves while you type.
- To place passive entries and exits at exact levels in the order book.
Example: the best ask is 60,000. You send a post-only buy at 60,010. A normal limit buy would fill at 60,000 as a taker. The post-only order is rejected or canceled instead, so you can reprice.
The trade-off is that the order may not fill, and a fast market can cancel it more than once.
How do venues name it?
| Venue | Post-only setting |
|---|---|
| Binance (USD-M) | Time in force GTX |
| OKX | Order type post_only |
| Hyperliquid | Time in force “Post Only (ALO)”: the order is added to the book and never executes immediately |
| Bybit | Time in force PostOnly |
Exact rejection behavior differs by venue. Some cancel the order and some reject it with an error. Read your venue’s API notes.
Frequently asked questions
Does post-only guarantee a fill?
No. It only guarantees that the order will not take liquidity. It can stay unfilled, or be canceled if its price would match at once.
Is a post-only order always cheaper?
It pays the maker rate instead of the taker rate, which is usually lower, and some venues pay rebates to makers. Fee schedules differ, so check your tier.