What is token approval, and why can it remain active?
An ERC-20 approval gives another address permission to spend a specified token balance up to an allowance. That permission can outlast the transaction you intended.
In brief
A decentralized exchange, bridge or marketplace may ask for an approval before the intended transaction. The approval records permission in the token contract: a particular address may spend up to a specified amount from your balance.
The application can subsequently use that allowance to transfer tokens.
What the standard says
ERC-20 was proposed by Fabian Vogelsteller and Vitalik Buterin on 19 November 2015. Its approval mechanism permits a spender to withdraw repeatedly, up to the approved amount.
Permission can remain after a transaction if an allowance remains. The standard's allowance function exposes how much the spender can still withdraw. This is readable on-chain data, not an estimate.
Why applications request large allowances
A large or effectively unlimited allowance avoids asking for another approval before every transaction, saving an extra transaction and fee.
The trade-off is continuing authority over that token balance up to the allowance. Finishing an interaction with an application does not itself revoke the permission.
The standard's warning
ERC-20 advises interfaces to set an allowance to zero before changing it to another value, addressing the risks around changing an existing allowance. That warning should be distinguished from a guarantee that an interface or contract is safe.
What to check
- Which token the approval applies to.
- The actual spender address, not merely the project's name.
- The amount approved and the remaining allowance.
Risks
Biggest uncertainty The risk depends on the spender contract and its controls. No individual contract is assessed here.
An approval may remain usable after the original interaction. If the spender is upgradeable, its implementation may change while the permission still belongs to the same address.
A claim or mint screen can conceal a request for spending authority. Inspecting the underlying call matters more than the wording on the page.
This guide does not evaluate individual contracts, wallet interfaces or revocation tools. ERC-721 and ERC-1155 operator approvals are outside its scope.
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