What is a token approval, and why can it outlast the trade?

The first time someone swaps a token on a decentralised exchange, the wallet often asks for two confirmations rather than one. The second is the swap itself. The first is easy to click past, and it is the one that can outlast the trade by years: a token approval.

What is a token approval?

A token approval is a standing permission that lets a named smart contract move up to a set amount of a specific token out of a wallet without asking the owner again. The owner grants it once. From then on the approved contract can draw on it whenever its own code decides to.

Approvals exist because of how the standard behind most Ethereum tokens was designed. That standard gives a token two ways to move: the holder sends it directly, or the holder first approves a spender and the spender then pulls the tokens itself. The second route is what lets an exchange contract, a lending pool or a bridge take tokens as one step of a larger operation.

Why does a swap need an approval first?

A swap needs an approval because an exchange contract cannot take tokens it has not been allowed to take. Sending tokens straight to the contract would not tell it what to do with them. So the pattern is to approve first, and then call the contract, which pulls the tokens and completes the swap in a single transaction.

The approval and the swap are separate transactions, and each pays its own gas fee (opens in a new tab). Some tokens support a signed permit instead. The holder signs a message granting the approval, and the contract submits that signature alongside the trade. Creating the signature costs nothing, which is convenient and is also the reason permits turn up in phishing, as a later section explains.

What is an unlimited approval?

An unlimited approval grants a spender the right to move the largest amount of a token the standard can represent. In practice, that means every unit the wallet holds now or receives later. Many apps request it by default, so a returning user does not pay for a fresh approval on every trade.

The cost of that convenience is duration. An approval does not end when the trade finishes, when the browser tab closes, or when the user stops using the app. The original token standard has no expiry field at all. An unlimited approval granted to a contract years ago still stands today unless its owner has revoked it.

How do approvals get exploited?

Approvals get exploited in two main ways: the approved contract later turns out to be flawed, or the approval was granted to an attacker in the first place.

In the first case a legitimate app's contract is exploited after the fact, whatever its audit (opens in a new tab) covered. Every wallet that left an unlimited approval with that contract is exposed, including wallets whose owners have not opened the app in months. Nobody sent those funds anywhere. The old approval did the work.

The second case is approval phishing. A convincing copy of a real app asks the visitor to connect a wallet, and confirm what looks like a routine step. The confirmation is an approval or a signed permit naming the attacker's contract as the spender. Toolkits built for this are widely called wallet drainers. A signed permit is especially easy to miss, since it can look like a harmless message and costs nothing to sign.

Neither case involves stealing a private key. The owner authorised the spender, and the blockchain enforces that authorisation exactly as written.

How do you check or revoke an approval?

Approvals are public on-chain records, so any holder can list the ones attached to an address. A block explorer (opens in a new tab), or a dedicated approval checker reads those records and shows each spender, each token and the allowance left.

Revoking an approval means setting its allowance back to zero. That is itself an on-chain transaction with its own gas fee. Revocation stops future withdrawals only: it cannot recover tokens a spender has already moved.

Some wallets also let the owner edit the amount before confirming an approval. A swap can then approve what that one trade needs rather than an unlimited sum. Exposure shrinks to the size of the trade, at the cost of approving again next time.

Where Northtape fits

Northtape connects to no wallet and asks for no token approvals. It is a news desk. Stories about exploited contracts and drained wallets are detected by the Risk Radar protocol lens.

FAQs

Is approving a token the same as sending it? No. An approval moves nothing on its own. It authorises a named contract to move tokens later, up to the approved amount.

Does a token approval expire? Not under the original token standard. It lasts until the owner revokes it or replaces it with a new amount.

Does revoking an approval get stolen tokens back? No. Revoking stops the spender from moving anything further, and tokens already moved stay where they went.

Is a signed permit safer than an on-chain approval? Not inherently. A permit grants the same power as an approval, and the fact that it costs nothing to sign makes it easier to grant by mistake.

None of this is investment advice. It describes how token permissions work on smart contract blockchains, not whether to use any app, token or wallet.