The network charges for a write to the ledger. The fee is in its coin, not in “whatever you are swapping”.

  • Ethereum and L2s like Base / Arbitrum: ETH (on an L2 — that chain's ETH).
  • BNB Chain: BNB.
  • Solana: SOL.
  • TON: TON.
  • Sui: SUI.
  • Tron: TRX (sometimes energy, but you will not get far with zero TRX).

Why the number jumps

Gas follows congestion. Ethereum at peak is dearer than Base. Solana is usually pennies until priority fees get bid up. That is not Uniswap “being greedy” — that is the network.

How not to overpay and not to get stuck

  1. Network first, token second. Right address, right chain, then the amount.
  2. Keep enough native on the address for several transactions, not one “exactly”.
  3. Read the fee in the wallet before you sign. If you see three extra zeros after the swap amount, you are in the wrong place.

Without this step the Uniswap and Jupiter guides are useless: Swap stays grey or the transaction fails.