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Using Block Explorers with MetaMask: Etherscan & 'Write Contract'

Dustin Bennett Dustin Bennett
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Why use Etherscan with MetaMask?

Etherscan is a block explorer and verified-contract UI for Ethereum (and EVM-compatible) networks. Paired with MetaMask as your software wallet, it lets you bypass a dApp front end and interact directly with contract functions (read or write). That can be safer when a site’s UI is broken or you suspect front-end tampering. I use this combo regularly to check allowances and to call approve() or revoke functions when a dApp’s interface fails. Short sentence.

But direct contract calls carry risk too. Always verify the contract source is published and double-check addresses before signing a transaction.

How Etherscan’s Read vs Write Contract works

  • Read Contract: public, free, no gas — call view/pure functions like balanceOf() or allowance(). You don't need to connect your wallet to read data.
  • Write Contract: sends on-chain transactions (requires gas) and requires a Web3 provider connection so MetaMask can sign the transaction. Only available when the contract source ABI is verified on Etherscan.

(If a contract is unverified, Etherscan hides the Read/Write UI; you’ll see bytecode only.)

Connect Etherscan to MetaMask (desktop) — step by step

  1. Open the contract or token page on Etherscan (desktop browser).
  2. Click the "Contract" tab, then the "Write Contract" tab.
  3. Click "Connect to Web3" (top right). MetaMask extension will prompt to connect — select the account and approve.
  4. Fill function inputs (e.g., approve(spenderAddress, amount)) and click "Write".
  5. MetaMask opens a transaction confirmation modal. Review gas limits, maxPriorityFee and maxFee (EIP-1559 fields), then confirm.

What I've found: confirm the network in MetaMask matches Etherscan (e.g., Ethereum Mainnet vs a testnet). If they disagree the write UI will not work.

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Etherscan + MetaMask mobile: two ways to connect

Mobile is different because most mobile browsers don’t inject MetaMask as a provider. You have two reliable options:

  • Use the MetaMask mobile in-app browser. Open MetaMask (iOS/Android) -> Browser -> visit etherscan.io -> find the contract -> the site will detect the injected provider and "Connect to Web3" will link immediately.
  • Use WalletConnect from the Etherscan site (if available). On desktop Etherscan shows a QR code for a WalletConnect session; scan with MetaMask mobile to connect.

And yes, I’ve used both. I prefer the in-app browser when I need to quickly call approve() from my phone. It’s faster. (But the WalletConnect route is useful when you don’t want to open the in-app browser.)

![Etherscan Write Contract UI - placeholder image]

Check token approvals with Etherscan (practical steps)

Method A — Read Contract allowance():

  1. Open the token contract page on Etherscan.
  2. Contract → Read Contract.
  3. Find allowance(address owner, address spender).
  4. Paste your wallet address as owner and the dApp/spender address to check the approved amount.

This is read-only. It costs nothing and is precise: you get the exact uint256 value recorded on-chain.

Method B — Token Approval Checker (where available):

Etherscan exposes token-approval summary pages for addresses on some networks. That interface aggregates approvals so you can see multiple spender addresses at once. If present, it speeds audits. If you don’t see it, use allowance() manually.

Revoke or change approvals via Write Contract (step by step)

Typical revoke pattern: set allowance to 0.

  1. On the token contract page choose Contract → Write Contract.
  2. Click "Connect to Web3" (MetaMask will prompt).
  3. Find approve(spender, amount) or decreaseAllowance/increaseAllowance depending on the token.
  4. For a revoke, set amount = 0 and submit.
  5. Confirm the transaction in MetaMask and pay gas. On Ethereum mainnet expect ~40k–100k gas for approve-type calls; L2s and sidechains will be significantly lower.

Notes: some tokens implement non-standard allowance functions—if approve() is not present, look for increaseAllowance/decreaseAllowance or check the token’s documentation.

If you prefer a guided walkthrough, see the step-by-step revoke guide: how-to-revoke-approvals-step-by-step and the background page token-allowances-and-revoke.

Comparison: Etherscan vs in-wallet UI vs dApp front end

Method Requires verified ABI Ease of use Front-end risk Notes
Etherscan Write Contract Yes Moderate Lower (direct contract interaction) Good for direct calls and repairs when a dApp UI breaks.
MetaMask approval UI (in-wallet) No Easy Moderate Convenient; sometimes incomplete aggregator of approvals.
dApp front end No Easiest Higher Quick, but could be malicious if the site is compromised.

Common problems & quick fixes

  • "Write Contract" disabled: contract not verified. Solution: use another tool (e.g., Remix or a trusted UI) or obtain the ABI elsewhere.
  • Wrong network: switch MetaMask to the contract’s network (check the top-left chain selector).
  • Transaction keeps failing: check the tx receipt on Etherscan (gas used vs gas limit) and review revert reason if available.
  • MetaMask not prompting on mobile: open Etherscan inside MetaMask’s in-app browser or use WalletConnect.

Check the security checklist before you sign: security-checklist.

FAQ

Q: Is it safe to keep crypto in a hot wallet? A: Hot wallets like MetaMask are convenient for daily DeFi use but carry higher risk than hardware wallets. For frequent swaps and dApp access a hot wallet is practical. For large long-term holdings, consider moving funds to hardware wallets. (See the hardware wallet pages linked in our site.)

Q: How do I revoke token approvals via MetaMask? A: You can revoke from a wallet's approvals UI if available, use Etherscan's Write Contract to call approve(spender, 0), or follow the step-by-step guide: how-to-revoke-approvals-step-by-step.

Q: What happens if I lose my phone? A: If your seed phrase is backed up you can restore on a new device. If not, funds are unrecoverable. See seed-phrase-backup-recovery for secure backup practices.

Conclusion & next steps

Using Etherscan with MetaMask gives you precise control over contract interactions: check allowances, call approve/revoke, and bypass a dApp front end when necessary. In my experience this workflow reduces surprises (like hidden approvals) if you take a deliberate, step-by-step approach. Want a practical revoke walkthrough or mobile setup tips? Follow these links: how-to-revoke-approvals-step-by-step and metamask-mobile-ios-android.

And remember: always verify the contract source, double-check addresses, and never share your seed phrase. Safe on-chain work starts with careful checks.

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