ImpactSplit

How it works

Market microstructure has separated two things for forty years that every AMM still treats as one. When a trade moves a price, part of that move is information, and the price stays where the trade put it. The rest is the cost of demanding liquidity right now, and the price comes back.

The first is called permanent impact and the second temporary, and the distinction is the whole reason a market maker can quote at all: they lose to the first and earn from the second. An AMM charges a fee on size and calls it done. Size is a bad proxy for either component.

A large trade in a deep pool moves nothing and pays the same rate as a small one that moves the price a long way, and a pool that raises its fee with volatility charges the informed and the uninformed identically because at the moment of the swap they are indistinguishable. They are indistinguishable at that moment. They are not indistinguishable later.

This hook charges every swap for the impact it causes, holds the charge, and then looks again after a settlement window: whatever share of the move has survived is paid to the liquidity providers who wore it, and whatever share has decayed is returned to the trader who was only ever renting liquidity. Nobody has to guess which kind of flow arrived. The price says so, afterwards, for free.

A trader who moves the price and is right pays. A trader who moves the price and is wrong is refunded and has paid only the pool's ordinary fee. That is the correct answer in both cases, and it is not reachable by any rule that has to decide at swap time.

Using it

Uniswap v4 removed hookData from initialize, so per-pool parameters arrive out of band. Fix them for a pool key whose pool does not exist yet, then initialize. Nobody can change them afterwards, including you.

hook.configure(
    key,
    ImpactSplitHook.Config({
        maxImpactFee: /* uint24 */ 0,
        halfPointTicks: /* uint32 */ 0,
        windowSeconds: /* uint32 */ 0,
        minTicks: /* uint32 */ 0
    })
);

poolManager.initialize(key, startingSqrtPriceX96);

Parameters

From TypeScript

npm i @hookforge/sdk

import {getHook, hookAddress, poolKeyFor} from "@hookforge/sdk";

const hook = getHook("impact-split");
const key  = poolKeyFor({
  hook: hookAddress("impact-split", 8453),   // Base
  currencyA: USDC, currencyB: WETH,
  tickSpacing: 60,
});

What it reverts with

The callbacks it claims

Uniswap v4 reads a hook's permissions from the low fourteen bits of its own address, which is why deploying one means mining a CREATE2 salt. This hook claims 4, so every deployment of it has an address ending in 0x10c4.

• beforeInitialize
• afterInitialize
• beforeAddLiquidity
• afterAddLiquidity
• beforeRemoveLiquidity
• afterRemoveLiquidity
• beforeSwap
• afterSwap
• beforeDonate
• afterDonate
• beforeSwapReturnsDelta
• afterSwapReturnsDelta
• afterAddLiquidityReturnsDelta
• afterRemoveLiquidityReturnsDelta

It says what it is, on-chain

Nothing about a hook's address tells an indexer, a wallet, a router or an agent what the pool does, which is why hook discovery today is a curated list. This hook answers for itself, in one eth_call, with no registry in the loop.

cast call $HOOK "hookName()(string)"    # ImpactSplit
cast call $HOOK "specURI()(string)"     # https://impact-split.pages.dev/hook.json
cast call $HOOK "hookTags()(string[])"  # fees, price-impact, microstructure, rebate, no-admin

Build, test and deploy

git clone --recurse-submodules https://github.com/nirholas/impact-split
cd impact-split
forge build && forge test

# Dry run: mines the salt, prints the address, sends nothing.
forge script script/Deploy.s.sol --rpc-url $RPC_URL

# For real.
forge script script/Deploy.s.sol --rpc-url $RPC_URL --broadcast --verify

Try it

This is the hook running, not a picture of it. Connect a wallet on a chain it is deployed to, or bring the whole stack up locally in one command and use it with no funds and no wallet risk at all.

git clone --recurse-submodules https://github.com/nirholas/impact-split
cd impact-split

anvil &
forge script script/DeployLocal.s.sol --rpc-url http://127.0.0.1:8545 --broadcast \
  --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80

node web/build.mjs && npx serve web/dist