Technical Definition

Token Approval

A token approval is an on-chain permission that a wallet owner grants to a smart contract, allowing that contract to transfer a specified (or unlimited) amount of a particular token (usually ERC-20) from the owner’s address.

By Crypto University Editorial
Allowancerevokewallet drainer

✦ Key Insight

Almost every DeFi interaction, swaps, lending, staking, requires an approval first. Without it, contracts cannot move your tokens. However, approvals create lasting risk: if the approved contract is later exploited or malicious, funds can be drained without further consent. For active traders, managing approvals is a core security hygiene practice.

✕ Common Misconceptions

Granting unlimited approvals by default; never reviewing or revoking old ones; approving unknown or phishing contracts; assuming disconnection from a dApp also removes the on-chain allowance.

Detailed Explanation

How It Works: The user signs an approve(spender, amount) transaction. This sets an allowance in the token contract’s storage. Later, the spender can call transferFrom up to that limit. Approvals persist indefinitely until revoked or reduced. Unlimited approvals are common for convenience but higher risk.

FAQs:
Does approval cost gas?

Yes.
Can it be limited?

Yes,set exact amounts when possible.
How long does it last?

Forever until changed or revoked.

In Practice

“Before swapping USDC for ETH on a DEX, a trader approves the router contract to spend USDC. The subsequent swap transaction then moves the tokens using that approval.”

Dig Deeper

dApp

A dApp (decentralized application) is a software application that runs on a blockchain network via smart contracts rather than centralized servers, giving users direct, permissionless interaction.

Allowance

An allowance is the specific quantity of tokens that a wallet has authorized a particular smart-contract address (spender) to transfer on its behalf, as recorded in the token contract’s state.

Revoke

To revoke is the act of resetting a token allowance to zero (or a lower amount) via an on-chain transaction, permanently removing a smart contract’s permission to transfer the specified tokens from your wallet.

Wallet Drainer

A wallet drainer is a malicious smart-contract or phishing toolkit designed to trick users into signing transactions or approvals that immediately (or later) transfer all valuable assets out of their wallet to the attacker’s address.