JIT Liquidity (Just-In-Time Liquidity)

Just-In-Time Liquidity, or JIT liquidity, is a technique where a sophisticated actor provides liquidity to a pool immediately before a large trade is about to happen, and withdraws that liquidity immediately after, capturing most of the trading fees from that single transaction while contributing almost no ongoing liquidity to the pool. It exploits the public visibility of the blockchain mempool to time deposits and withdrawals with millisecond precision around profitable trades.

Here is how it works in practice. The JIT provider watches the mempool for large incoming trades. When one appears, the provider rapidly submits a transaction to add a huge amount of liquidity to the relevant pool, getting processed right before the big trade. The trade executes against the now-much-deeper pool, paying fees proportionally distributed to all current liquidity — including the freshly added JIT liquidity. Immediately after, another transaction removes all that liquidity. The JIT provider earned fees from a trade they did not really support with sustained capital.

JIT liquidity is controversial because it extracts fee income from long-term liquidity providers who bear the real risks of the pool — including impermanent loss — by interposing at the last moment for cream-skimming. It is a form of MEV (see Maximal Extractable Value). Protocols have explored various defenses, including minimum liquidity durations and fee structures that favor long-term providers, but the practice persists wherever mempools are visible and block producers have ordering flexibility.

Example: Imagine a small bakery that charges a 10% service fee to every customer. You run a catering business. Every morning, you watch who lines up outside. The moment you see a large corporate order walking toward the door, you rush in, temporarily buy a half-share of the bakery, collect your cut of the huge fee from the corporate order, then immediately sell your share back. The original baker did all the actual baking; you just timed your share ownership to scoop the big commission.