What a hook can do to your swap

A hook runs inside your swap

A Uniswap v4 pool can name a hook: a contract the PoolManager calls at fixed moments, such as just before and just after each swap. Whoever deploys the hook decides what that code does. On Robinhood Chain most pools trade through one, including every Pons launch. Your wallet shows you the router, not the hook, so the code that decides part of your fill is usually the one you never see.

The four that matter

Of the 14 permissions a hook can have, four touch the person swapping directly:

• Can change the price you get (beforeSwapReturnsDelta): the hook adds or removes tokens before the pool fills you.
• Can take a fee from your output (afterSwapReturnsDelta): after the fill, it keeps part of what you were about to receive.
• Can block swaps (beforeSwap, afterSwap, or gated access): it can revert, which makes your swap fail.
• Can change the fee each swap (a dynamic-fee pool): the LP fee is whatever the hook sets for that swap.

On top of that, an upgradeable hook can be replaced by its owner, so today's behaviour is not a promise for tomorrow.

The card before you sign

A real unlisted hook

Hook 0x8aa375f7186f86bbac7b13ab01db189ebe50c0c4 sits behind 1,479 pools on Robinhood Chain and is in no registry. The last four hex digits of its address, c0c4, set three swap permissions: it runs before and after every swap and can take a cut of the output.