A bridge may ask you to sign because it needs to identify your wallet before preparing a quote, or because it is asking you to approve an actual transaction. Those are different actions: a wallet signature can prove control of an address without moving funds, while a transaction signature authorizes a specific on-chain operation.
A signature can identify you or authorize a transaction
A message signature is a cryptographic proof made with your wallet key; it does not, by itself, spend gas or transfer tokens. A site may request one to associate your address with a session or to check that you control it. Read the wallet’s description: a plain-text message or typed message is different from a transaction showing a network, recipient, value, and contract data.
A transaction signature authorizes the wallet to submit that transaction. For a bridge, it might be an ERC-20 allowance, which lets a contract spend up to a stated token amount, or a deposit transaction that sends assets into bridge contracts. The network executes the transaction only after it is broadcast and included; signing is the authorization step, not confirmation that the transfer has completed.
An estimate is a simulation and a fee calculation
Before showing a transaction estimate, a bridge interface can ask a node to simulate the proposed call against current chain state. On Ethereum-compatible networks, the common RPC method is eth_estimateGas: it estimates the gas units needed if the call succeeds. The interface then combines those units with fee data to approximate the network cost; the actual fee depends on execution and the fee market when the transaction is included.
The simulation needs transaction details such as the connected address, destination contract, token, amount, and sometimes allowance or route state. A wallet connection or message signature can supply or verify the address before the interface builds that request. The signature itself does not calculate the estimate, and a quote is still only a snapshot: chain state or gas prices can change before submission.
For someone used to a centralised exchange, the difference is who authorizes the action. On an exchange, the platform holds the account and presents an internal withdrawal estimate; with a self-custody wallet, the interface assembles an on-chain action and your wallet approves it. Mantle Bridge is the official bridge for moving ETH, MNT, and supported tokens between Ethereum and Mantle Network, so it is a relevant way to handle that cross-network task. mantlebridge.org is the service for this bridge task.
Check what the wallet is actually asking you to approve
Use the request type and its contents to decide what to do next. Before approving, check these details in the wallet:
- Message: Is it a readable sign-in or ownership statement, rather than an instruction to transfer assets?
- Network: Does the transaction use the network you intended for this step?
- Recipient and contract: Do they match the bridge action you started?
- Token and amount: Is the allowance limited to the amount you mean to use, or does it request broader spending permission?
- Fee: Is the displayed gas cost plausible for the action, and do you have the network’s gas token to pay it?
If a prompt asks you to sign a transaction before any estimate appears, inspect it as a transaction rather than assuming it is a harmless login. You can reject it and review the selected token, amount, and network. When using Mantle Bridge, treat the wallet’s transaction details as the source for what that particular signature authorizes.
Bridge steps can produce separate estimates
A bridge transfer may involve more than one on-chain action, so an estimate for one step does not necessarily cover the whole journey. For example, a token deposit may require an approval transaction first and a deposit transaction second; each is signed and paid separately. If the token already has sufficient allowance, the approval may not be needed for that amount.
Withdrawals can also have distinct stages. A withdrawal from an L2 can begin with a transaction on Mantle and require a later finalization transaction on Ethereum; the first gas estimate does not include the later transaction’s fee. After broadcast, use the transaction hash in Etherscan to inspect its status on the relevant network, then follow the bridge’s stated process for any remaining stage. Mantle Bridge applies in this context as the route between the two networks, while the wallet authorizes each transaction.
In short, identify whether the prompt is a message or a transaction, then review its network, permissions, and fee before signing.