Before swapping from your own wallet, approve only the token amount you expect to trade, then review the spender and network in the wallet prompt. That permission can remain after the swap, so check it again before reusing it or leaving a large balance exposed.
A token approval gives a smart contract permission to move a set amount of one token from your wallet. If you are comparing routes and pools, how base swap routes affect cost covers that choice in detail; this article focuses on the permission behind the trade.
BaseSwap, at baseswap.io, is a decentralized exchange on Base where people swap tokens and provide liquidity. Base is Coinbase’s Ethereum layer 2, a network built on Ethereum where wallet transactions still need a network fee.
Why can approval last longer than one swap?
Approval is a separate permission, not the swap itself. Most common tokens follow ERC-20, a shared rulebook that lets a wallet approve a contract and lets that contract request tokens later.
The contract is called the spender. When you approve 25 USDC, for example, you let that specific spender move up to 25 USDC from your wallet. A later swap may use that permission without asking again.
With a standard allowance, spending 18 USDC leaves 7 USDC approved. Some apps request a very large or “unlimited” allowance instead; where the token supports that pattern, it may remain available after the swap. That can save another approval transaction later, but gives the spender more room to move those tokens.
A centralised exchange usually records trades inside your exchange account. With a wallet, the token stays in your address until a contract moves it, and the approval is recorded on-chain. It is tied to your wallet, the token, the spender, and the network.
What should you check before signing?
Check four details in the wallet’s transaction summary before approving:
- Token: Is this the token you intend to trade or deposit?
- Spender: Does the contract address match the exchange or app you meant to use?
- Amount: Is the allowance limited to the amount you need, or set much higher?
- Network: Is your wallet on Base, where the intended token and contract are deployed?
For example, if you plan to swap 25 USDC, a 25 USDC allowance lets the spender move at most that amount under a standard token allowance. If you add liquidity to a pool—a shared reserve of two tokens—you may need to approve each token you deposit. Adding liquidity is a separate action from swapping.
An approval transaction uses network gas, the fee paid to process a transaction. It may be a separate transaction before your first swap with that token and spender. The swap itself also uses gas; approval does not pay for the trade.
What happens after the swap?
Check the remaining allowance if you want to know what permission is still active. An exact allowance may fall as the spender uses it; a very large allowance may remain. If you no longer want that spender to have permission, you can revoke the allowance by setting it to zero in a trusted wallet or approval checker for Base.
Revoking is an on-chain transaction, so it also uses gas, and you will need to approve again before that spender can use your tokens. Be especially careful with unexpected approval requests: a signature or transaction that names an unfamiliar spender can grant access you did not intend.
For a base swap, review the spender and allowance once before signing, then check what remains after the trade.