Fuel
Every leg burns fuel. The fuel is a slice of the ETH side of the trade — buying or selling — and it is never the token. It sits in the tank until anyone pumps it to one immutable address.
The tank
read from the fuel hook
- —
- In the tank
- —
- Pumped
- —
- Goes to
banked, not yet pumped
over the hook's life
immutable, no setter
Whoever presses this pays the gas. The ETH goes to the address above regardless — there is no recipient argument to give it.
Recent burns
every router, every pool
Nothing burned yet.
Why ETH
A launchpad paid in the tokens it launches has to sell them, and the only place to sell them is the pool it just charged. This one is paid in ETH on both legs, so the wallet the fuel goes to never holds a single wing it would need to dump.
The four shapes
- Buy, exact input. ETH is named. The fuel comes off the top before the curve sees it.
- Sell, exact input. Wings are named; ETH comes out. The fuel comes off what the curve paid.
- Buy, exact output. Wings are named; ETH goes in. The fuel is added on top of what the curve charged.
- Sell, exact output. ETH is named. The hook asks the curve for a little more and keeps the difference.
The runway sends the first two; the hook prices all four.
Banked, then pumped
A pool holds no ETH until its first buy, and inside a swap the trader has not settled yet, so taking cash mid-swap would revert the first trade of every pool. The fuel is minted as an ERC-6909 claim against the pool manager and redeemed by pump, in a transaction of its own.