# OracleBand

> Refuses to let a pool settle at a price the wider market does not recognise.

A production Uniswap v4 hook. Source: https://github.com/nirholas/oracle-band. Part of the HookForge catalogue: https://hookforge.pages.dev

## How it works
A thin pool can be walked anywhere. Buy through the last tick of liquidity and the pool will quote you a price no other venue would, and whatever reads that pool afterwards, a lending market, a vault, another pool's oracle, inherits the number. The pool is not wrong: it faithfully reports what it was paid. It is simply alone. This hook gives the pool a second opinion. Before and after every swap it compares the pool price against a reference from an {IPriceOracle} and rejects the swap if the result lands outside a band around it:   deviation = |poolPrice / referencePrice - 1|, rejected when deviation > maxDeviationBps The check runs on both sides of the swap, and the pair is what makes it hard to defeat. The `beforeSwap` check refuses to trade from a price that is already outside the band, so a pool pushed out of line in one transaction cannot be traded against in the next. The `afterSwap` check refuses to leave the pool outside the band, which is what stops the walk in the first place. Neither check can be satisfied by splitting a large swap into small ones, because the constraint is on the resulting price rather than on the size of the trade. Prices are compared in `sqrtPriceX96`, squared back through `FullMath` so the comparison is on the actual price ratio and not on an approximation of it that drifts as the deviation grows. Liquidity operations are untouched. A provider can always withdraw, including while the band is refusing swaps, which is the property that makes it safe to sit behind one. The obvious objection: this makes the pool depend on an oracle, and oracles fail. So the hook treats failure as refusal rather than as permission. A feed older than `maxStaleness` halts swapping instead of waving it through, and a feed that reverts propagates rather than being caught. A pool that would rather trade blind than not trade should not use this hook, and the fee-based hooks in this catalogue are the oracle-free alternative.

## Prior art
Oracle-deviation checks exist inside individual protocols, and Detox uses Pyth to detect MEV and redirect it. Both act after the fact, on a pool that has already printed the price. Enforcing the band as a precondition on both sides of the swap, so the out-of-band price is never written at all, is what is new here.

## Where it does not help
The pool inherits the oracle's liveness. If the feed stops, swapping stops, and on a chain where the feed updates on a deviation threshold rather than a heartbeat, a quiet market can look stale. Set maxStaleness against the feed's actual publication cadence, not against how fresh you would like it to be.

## Facts
Slug: oracle-band
Contract: OracleBandHook
Callbacks: afterSwap, beforeSwap, afterInitialize
Parameters: oracle (address), maxDeviationBps (uint32), maxStaleness (uint32)
Dynamic fee required: no

## Caveats
- Unaudited.
- A deployment with status "deterministic" is a mined CREATE2 address with no code at it yet. Never present one as live.