Hook contract rules

This page is for people who read or edit the Solidity. It lists what a hook must look like to compile and deploy in the app.

Compiler

Setting	Value
Compiler	solc 0.8.26
EVM version	cancun
Optimizer	on, 200 runs
IR pipeline	used automatically if the default pipeline reports "stack too deep"

The hook must be a single file.

Available imports

Import prefix	Library
@uniswap/v4-core/src/...	Uniswap v4-core 1.0.2
@uniswap/v4-periphery/src/...	Uniswap v4-periphery 1.0.3
@openzeppelin/contracts/...	OpenZeppelin Contracts 5
solmate/src/...	Solmate
permit2/src/...	Permit2

Nothing else can be imported. Test helpers and forge-std are not available.

Structure

• Inherit BaseHook from @uniswap/v4-periphery/src/utils/BaseHook.sol.
• Override the internal callbacks (_beforeSwap, _afterSwap and so on), not the external ones. BaseHook already restricts them to the PoolManager.
• SwapParams and ModifyLiquidityParams come from @uniswap/v4-core/src/types/PoolOperation.sol.
• getHookPermissions() must return true for exactly the callbacks the hook implements. A mismatch makes the deployment revert.

Constructor

Use one of these two forms:

constructor(IPoolManager _poolManager) BaseHook(_poolManager) {}

constructor(IPoolManager _poolManager, address _owner) BaseHook(_poolManager) {
    owner = _owner;
}

The app passes Robinhood Chain's PoolManager and, for the second form, your wallet address.

Do not use msg.sender as the owner

Hooks are deployed through a CREATE2 deployer contract, so msg.sender in the constructor is that deployer, not you. Take the owner as a constructor argument.

Callback signatures

function _beforeInitialize(address, PoolKey calldata, uint160) internal returns (bytes4);
function _afterInitialize(address, PoolKey calldata, uint160, int24) internal returns (bytes4);
function _beforeAddLiquidity(address, PoolKey calldata, ModifyLiquidityParams calldata, bytes calldata) internal returns (bytes4);
function _beforeRemoveLiquidity(address, PoolKey calldata, ModifyLiquidityParams calldata, bytes calldata) internal returns (bytes4);
function _afterAddLiquidity(address, PoolKey calldata, ModifyLiquidityParams calldata, BalanceDelta, BalanceDelta, bytes calldata) internal returns (bytes4, BalanceDelta);
function _afterRemoveLiquidity(address, PoolKey calldata, ModifyLiquidityParams calldata, BalanceDelta, BalanceDelta, bytes calldata) internal returns (bytes4, BalanceDelta);
function _beforeSwap(address, PoolKey calldata, SwapParams calldata, bytes calldata) internal returns (bytes4, BeforeSwapDelta, uint24);
function _afterSwap(address, PoolKey calldata, SwapParams calldata, BalanceDelta, bytes calldata) internal returns (bytes4, int128);
function _beforeDonate(address, PoolKey calldata, uint256, uint256, bytes calldata) internal returns (bytes4);
function _afterDonate(address, PoolKey calldata, uint256, uint256, bytes calldata) internal returns (bytes4);

Good practice

• Keep storage per pool, keyed by PoolId (key.toId()), since one hook can serve many pools.
• Hooks run on every swap. Keep callbacks cheap.
• Do not let a callback revert on ordinary swaps unless blocking them is the point.
• If the hook uses a return-delta permission, settle every amount it creates.
• Cap anything configurable, such as a fee, in the contract itself.