Four Checks Before You Approve a Bridge Spender

Before approving a bridge route, check which token the spender can move, on which chain, and up to what amount. For ERC-20 tokens, approve sets an allowance for a spender address; the spender can then call transferFrom to move tokens from your wallet. The approval is a separate on-chain transaction from the bridge transfer, so it can remain in place after the route finishes.

A quote describes a proposed trip: the source token and amount, a route, and the expected destination asset. The route’s transaction data tells the source-chain contract how to carry it out. The spender is the address allowed to pull the source tokens; it may not be the same address that receives or processes the bridge transaction. For a closer look at route selection and its cost trade-offs, see this bungee bridge explainer. The approval itself is more like a key with a spending limit than a one-time payment.

What does approving a bridge spender authorize?

An approval gives a specific contract permission to spend a specific token from your wallet, up to the allowance you set. The ERC-20 standard names the relevant functions: approve sets the allowance, allowance reports what remains, and transferFrom lets the approved spender use it. This permission applies on the token’s chain. It does not, by itself, approve a destination-chain transaction or guarantee that the route will complete.

Some routes use a signature-based method instead of a new approval transaction. Bungee’s documentation, for example, distinguishes traditional approvals from Permit2 signatures, which specify a token, amount and expiration. Check what your wallet is asking you to sign: a token allowance and a message signature grant permissions in different ways.

Which four details should you check before signing?

Read the approval prompt alongside the route details. Check these four items before you confirm:

• Source chain and token. Make sure your wallet is on the route’s source chain and that the token contract address matches the asset you intend to bridge. A ticker or token name alone does not identify a contract.
• Spender address. Compare the approval’s spender with the address specified for that route by the bridge’s official interface or documentation. Do not assume the spender is the bridge brand, or that an address from another chain or route is valid here.
• Allowance amount. Check whether the approval is limited to the route’s input amount or grants a much larger allowance. A larger limit can save a later approval transaction, but it also gives the spender permission to move more of that token while the allowance remains.
• Bridge transaction. Check the separate transaction’s destination, token amount, destination chain and recipient. The approval lets a spender pull tokens; the bridge transaction carries out the route. An approval alone does not confirm those route details.

What happens to the allowance after the bridge?

A limited allowance is reduced as the approved spender uses it. An unused portion can remain available, and an unlimited allowance can remain after the transfer. You can check the token’s allowance for your wallet and the spender on the source chain; if you no longer want that permission, set the allowance to zero using a trusted wallet or token interface.

For most users, approving only the amount needed for the route is the clearer choice. It may require another on-chain approval later, but it limits what that spender can draw under that grant. If the address, token, chain or amount in the approval prompt does not match the route you selected, do not approve it until you can verify the mismatch.