Post-Only

A post-only order is a limit order that is guaranteed to add liquidity to the order book rather than take it. If a post-only order would immediately match against an existing resting order (i.e., cross the spread), the entire order is canceled without generating any fills.

How It Works

When you submit a post-only order, the matching engine checks whether the order would execute immediately:

• If the order would not cross the spread, it is placed on the order book as a resting limit order, adding liquidity. When it is eventually filled by an incoming taker order, you pay maker fees.

• If the order would cross the spread, the order is rejected entirely. No portion of the order is filled, and no fees are charged.

When to Use Post-Only Orders

Post-only orders are primarily valuable for:

• Ensuring maker fees — Maker fees are lower than taker fees. By using post-only orders, you guarantee that you will never inadvertently pay the higher taker fee.

• Market making strategies — Professional market makers and algorithmic traders use post-only orders to maintain resting liquidity on both sides of the order book without the risk of unintended taker fills.

• Precise entry prices — If you want to buy at a specific price or better and are willing to wait for the market to come to you, a post-only order ensures your order rests passively until filled.

Relationship to GTX Time-In-Force

Post-only orders and GTX (Good-Til-Crossing) orders are functionally equivalent. Both ensure that the order only adds liquidity and is canceled if it would cross the spread. The terms are interchangeable in the context of Katana Perps.