What a token approval does before a bridge

A token approval lets a bridge contract move a specified token from your wallet before the bridge transfers it to another network. For exchange users moving funds from a self-custody wallet, that permission is separate from the bridge transaction and may require its own network fee.

Why does a bridge ask for token approval?

The ERC-20 standard defines an approve function that sets how much a named spender can take from an account. A bridge’s contract needs that allowance to transfer the token you want to bridge; it does not grant access to every asset in your wallet.

On many networks, the approval is an on-chain transaction paid for in that network’s native coin. The bridge transfer follows as a separate transaction. A wallet connection alone does not create this token allowance, according to MetaMask’s guidance on approvals.

Bridge flows often combine a token transfer with steps that lock or burn assets on the source network and release or mint assets on the destination. The approval applies to the token and spender shown in the wallet prompt, not to destination gas or the bridge’s entire process. For a related example, Biswap’s guide to swaps without destination gas covers what a user may need on the receiving side.

What should you check before signing?

Read the wallet prompt and confirm the token, network, spender address and allowance amount. If the app offers a spending cap, set it to the amount you expect to use; a larger allowance can make repeat transfers easier, but leaves the contract permission to move more of that token.

• Check that the wallet is on the network where you hold the token.
• Match the token and amount to the bridge transfer you intend to make.
• Review the spender address and the app name shown by your wallet.
• Keep enough native coin on the source network to pay transaction fees.

These checks help catch a mismatched network, token or unexpected allowance before the transaction is sent. An approval cannot guarantee the bridge transfer will complete: the transfer is a separate operation with its own status.

Does the approval expire when the transfer ends?

Not necessarily. An allowance can remain after a bridge transfer, and disconnecting a wallet from an app does not itself revoke that on-chain permission, MetaMask says.

After you finish, review active allowances for the relevant network and revoke any you no longer want. Revoking changes the permission and requires another transaction, so it also uses network gas. For most users, a limited allowance is the clearer choice: it caps what the spender can transfer while avoiding a larger standing permission.