# Swap Against a StablePair Pool (/docs/protocols/uniswap-labs-hooks/stable-pair/guides/swap)

Quote and execute swaps against StablePair pools, including how to read the current dynamic fee.

Swapping against a StablePair pool uses the standard v4 swap path. The only difference is the fee: it is set by the hook at swap time, so it cannot be read from the pool key.

## Build the pool key
The pool uses v4's dynamic fee flag rather than a fixed fee tier. Code that assumes a static tier will not find the pool.

```solidity
PoolKey memory key = PoolKey({
    currency0: Currency.wrap(USDC),
    currency1: Currency.wrap(USDT),
    fee: LPFeeLibrary.DYNAMIC_FEE_FLAG, // 0x800000, not a fee tier
    tickSpacing: 1,
    hooks: IHooks(0x0000113dCf4ADd69999Fad8F20F2b63F979bfcC0)
});
```

## Read the current fee
`PoolKey.fee` holds the dynamic flag, not a rate. Instead, the hook exposes a view function returning the exact LP fee a swap will be charged in the current block, per direction:

```solidity
function getFee(PoolKey calldata key) external view returns (uint24 feeE6ZeroForOne, uint24 feeE6OneForZero);
```

Both values are returned in 1e6 precision, matching v4's own fee units.

For routers and aggregators this makes quoting substantially cheaper: the fee can be computed locally rather than simulated per size. Two properties are why.

* **Size-independent.** The fee never depends on the swap amount, so the same value applies to every size. `getFee` never reads a swap amount, and so never reverts on the basis of one.
* **Fixed for the block.** Both values are computed from the start-of-block price the next swap will see, so one read per pool per block covers every quote in that block. See [Block Price Caching](/docs/protocols/uniswap-labs-hooks/stable-pair/concepts/block-price-caching).

The two directions differ, often substantially (outside the band one of them is zero), so quote the direction being swapped.

`getFee` reverts with `PoolNotInitialized` if the pool was not initialized through the hook.

> [!NOTE]
> Two things the returned value is not. It is the LP fee only: if the pool has a protocol fee enabled, v4 compounds the two, taking the protocol fee from the input first and the LP fee from the remainder, and rounds the combined rate up to a whole pip. And it is pre price impact: the fee is exact, but the execution price still depends on the liquidity the swap traverses.

## Execute the swap
Swap through the standard v4 router or `PoolManager` unlock flow. StablePair holds no return-delta permissions, so it never alters swap amounts. It only overrides the fee.

## Where to Go Next
* [Dynamic Fees](/docs/protocols/uniswap-labs-hooks/stable-pair/concepts/dynamic-fees)
* [Provide Liquidity on StablePair](/docs/protocols/uniswap-labs-hooks/stable-pair/guides/provide-liquidity)