If you are depositing an ERC-20 and want fewer wallet transactions, a permit can authorize the spend with a signature, but only when the token and deposit flow support it. For an Ethereum-to-Mantle deposit, Mantle Bridge lets you choose a supported asset and amount; whether a permit saves an approval transaction depends on the token and the deposit flow.
What does a permit approve?
A permit is a signed token allowance: it lets a named spender use up to a stated amount of your tokens. Under the common ERC-2612 standard, your wallet signs typed data containing the token, owner, spender, amount, nonce and deadline. The token contract checks the signature and records the allowance on-chain when someone submits it.
The signature is not the deposit itself. A bridge still needs a transaction that transfers the tokens and starts the cross-chain deposit. If the deposit contract accepts a permit and uses it in that same transaction, the approval and deposit can happen together; the signature alone does not move funds or pay the transaction fee.
The ERC-2612 specification and OpenZeppelin’s implementation notes explain the key limit: the token must implement the permit interface. A wallet signing an approval message does not add permit support to a token, and a bridge interface must also be built to use it.
When can it replace a separate approval?
A permit can replace the separate on-chain approval transaction when three things line up: the exact token contract supports the permit format, the deposit flow accepts its signature, and the signature matches the spender and amount required for that deposit. If any one is missing, you will need the usual on-chain approval first.
For example, suppose you want to deposit 100 units of a supported ERC-20 from Ethereum. With a compatible permit flow, you could sign an allowance for 100 units, then confirm one Ethereum transaction that submits the permit and initiates the deposit. Without that flow, you first send an approval transaction, wait for confirmation, and then send the deposit transaction.
Check the wallet prompt carefully: the token, network, spender and amount should match the deposit you intend to make. For a one-off transfer, I prefer an allowance limited to the deposit amount over an unlimited allowance. A permit signature may be submitted by someone other than you, so its deadline should be short enough for the task, while still leaving time to complete it.
What can make the signature fail?
A permit is specific to its token contract and chain, and it uses a nonce to prevent the same signature being used twice. A signature can fail if its deadline has passed, the token’s nonce has changed, or the wallet signs data for the wrong token, network, spender or amount. If the wallet shows unfamiliar fields or an unexpected spender, stop and return to the deposit flow.
Permit support varies by token, even among familiar ERC-20 assets. Check the selected token’s contract and the deposit interface rather than assuming a ticker or symbol tells you enough. Some tokens also have different permit formats; a signature made for one format will not automatically work with another.
Smart contract wallets can be another edge case: some cannot produce standard ERC-2612 signatures. If the permit option is unavailable or fails, use the deposit flow’s regular approval route, if offered. For tokens that require an allowance to be reset before it is raised, follow the wallet’s requested approval steps and confirm each transaction before continuing.
How should you complete the deposit?
First, select Ethereum as the source network, the supported token and the amount. Check the destination address and keep enough ETH in your wallet for the Ethereum transaction fee; a permit can remove an approval transaction, but it does not make the deposit transaction free.
Next, use a permit only if the interface offers it for that exact token and deposit. Review the signature details, then confirm the transaction that submits the permit and starts the deposit. If the interface instead asks for an approval transaction, approve only the needed amount where possible, wait for confirmation, and then submit the deposit.
After submitting, use the transaction status shown by the bridge and wait for the deposit to complete before treating the funds as available on Mantle. In my place, I’d use a permit when the token and deposit flow clearly support it and the signed amount is limited to the transfer; otherwise, I’d use the standard approval flow and check each wallet prompt.
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