How to Check for Token Approvals on Your Wallet Contract?

Understanding Token Approval Mechanisms

1. Token approvals are permissions granted by users to smart contracts, allowing them to spend specific ERC-20 tokens on their behalf.

2. These approvals operate through the approve() function embedded in most token contracts, which sets an allowance for a designated spender address.

3. Once approved, the spender can call transferFrom() repeatedly up to the approved amount without further user interaction.

4. Approvals persist across transactions and remain active until explicitly revoked or overwritten with a zero-value approval.

5. The Ethereum blockchain stores all approval events as logs under the Approval event signature, making them publicly verifiable.

Tools for Detecting Active Approvals

1. Etherscan provides a dedicated “Token Approvals” tab on wallet address pages, listing all non-zero allowances grouped by token and spender.

2. Revoke.cash scans wallet addresses across multiple chains and highlights high-risk approvals—especially those granted to unknown or recently deployed contracts.

3. Blockchair supports approval lookups via its API and web interface, displaying both historical and current allowance values per token contract.

4. Wallet extensions like MetaMask do not display approvals by default but expose them through developer tools when inspecting transaction history or contract interactions.

5. Blockchain explorers such as Arbiscan and Basescan replicate Etherscan’s approval interface, adapted for Arbitrum and Base network-specific token standards.

Risks of Unchecked Token Approvals

1. Malicious contracts with unlimited allowances can drain entire token balances instantly, especially if the wallet holds multiple assets.

2. Phishing sites often trick users into approving tokens to seemingly benign addresses that later get repurposed for theft.

3. Exploited DeFi protocols may retain approvals even after exit, leaving residual access points for future attacks.

4. Front-running bots monitor pending approvals and execute transfers before the user realizes the scope of permission granted.

5. Some tokens implement custom logic where approvals interact unexpectedly with governance or staking modules, leading to unintended lockups or loss of control.

Manual Verification Using Web3 Libraries

1. Developers can use ethers.js to query the allowance() method directly: await tokenContract.allowance(walletAddress, spenderAddress).

2. A return value of 0 indicates no active allowance, while MaxUint256 signals an effectively unlimited approval.

3. Batch checking across multiple tokens requires iterating over known token contract addresses and invoking allowance() for each.

4. Integration with provider endpoints like Alchemy or Infura ensures low-latency responses when scanning dozens of contracts in sequence.

5. Custom scripts must handle decimals correctly—failure to normalize values against token precision leads to false positives in allowance interpretation.

Frequently Asked Questions

Q: Can I see approvals for tokens on Layer 2 networks using Etherscan?A: No. Etherscan only indexes Ethereum Mainnet. For Optimism, use Optimistic.etherscan.io; for Polygon, use polygonscan.com.

Q: Does revoking an approval cost gas every time?A: Yes. Each approve(spender, 0) transaction consumes gas, regardless of whether the previous allowance was zero or non-zero.

Q: Are NFT approvals visible the same way as ERC-20 approvals?A: Not exactly. ERC-721 approvals appear under getApproved() or isApprovedForAll(), requiring separate queries distinct from ERC-20’s allowance().

Q: Why does my wallet show “unlimited” when I only approved a small amount?A: Some interfaces misinterpret large integer values returned by contracts. Always verify raw output from allowance() rather than relying on UI labels.