Verify Crypto Transactions with a Block Explorer | Guide

You Wouldn’t Sign a Blank Check, So Why Are You Signing Blank Crypto Transactions?

Let’s be real for a second. In the world of crypto, your wallet’s “Sign” button is the most powerful—and most dangerous—tool you have. Every time you click it, you’re authorizing something to happen with your funds. A simple transfer, a token swap, a mint for a new NFT, you name it. But here’s the scary question: do you really know what you’re signing? Most people don’t. They see a popup from MetaMask, glance at the gas fee, and click approve. This is called ‘blind signing,’ and it’s like playing Russian roulette with your digital assets. Fortunately, there’s a powerful tool that acts as your X-ray vision into the blockchain: a block explorer. Learning how to use block explorers to verify transactions before you sign is the single most important security habit you can develop. It’s the difference between being in control and just hoping for the best.

This guide isn’t just about theory. We’re going to get our hands dirty. We’ll break down what a block explorer is, what to look for in a transaction, and how to spot the red flags that scream ‘scam!’ before you lose a single cent. Think of this as your personal pre-flight checklist for every on-chain action you take.

Key Takeaways

• Never ‘Blind Sign’: Always understand what a transaction does before approving it in your wallet. Relying on the dApp’s interface alone is a massive security risk.
• Block Explorers are Your Source of Truth: Tools like Etherscan, Solscan, and BscScan provide a raw, unfiltered view of the blockchain. What you see there is what will actually happen.
• Focus on the ‘To’ and ‘Data’ Fields: The destination address (‘To’) and the ‘Data’ field (which shows the function being called) are the most critical parts of a transaction to verify.
• Verification is a Skill: Learning to read a transaction on a block explorer takes a little practice, but it’s a fundamental skill for anyone serious about self-custody and DeFi.

So, What Exactly is a Block Explorer, Anyway?

Imagine the blockchain is a massive, transparent, and unchangeable public library. Every single transaction that has ever happened is a book on a shelf in this library, open for anyone to read. A block explorer is simply the library’s super-powered search engine and catalog. It’s a website that lets you browse, search, and inspect all of this on-chain data in a human-readable format. You can look up specific transactions, check the balance of any wallet address, inspect the code of a smart contract, and see what’s happening on the network in real-time. It’s the ultimate source of truth. While your wallet provides a convenient little summary, the block explorer shows you everything, warts and all.

Every major blockchain has its own block explorer. For Ethereum, the most famous one is Etherscan. For Solana, it’s Solscan. For the BNB Smart Chain, it’s BscScan. They might look slightly different, but they all serve the same core purpose: to make the blockchain’s data accessible and understandable. They are not wallets; you can’t initiate transactions from them. They are purely read-only windows into the chain’s activity.

The High Stakes of ‘Blind Signing’: Why You MUST Verify

Why is this so important? Because malicious actors are experts at making a dangerous transaction look harmless on the front-end of a website. You might think you’re just signing a message to log into a new platform, but in the background, you could be approving an infinite token spend, or worse, signing a transaction that drains your entire wallet.

The Drainer Scam

This is a classic. A scammer creates a convincing-looking fake mint site for a popular NFT project. You connect your wallet, excited to get in on the action. The popup appears, you see the expected price (say, 0.1 ETH), and you click ‘Sign’. Seconds later, you watch in horror as not just your ETH, but all your valuable NFTs and other tokens are transferred out of your wallet. What happened? The transaction you signed wasn’t a simple ‘mint’ function. It was a malicious contract call, like `setApprovalForAll` or a `transferFrom` function, that gave the scammer’s contract permission to take everything. Verifying the transaction on a block explorer would have revealed the true, malicious function being called.

The Infinite Approval Trap

When you use a decentralized exchange (DEX) like Uniswap for the first time, it asks for permission to spend your tokens (e.g., USDC). Often, to save on gas fees later, these dApps ask for an ‘infinite’ approval. This is convenient, but it’s also a ticking time bomb. If that DEX’s protocol ever has a vulnerability or is exploited, the hacker can use that pre-approved permission to drain the approved token from your wallet, even if you haven’t visited the site in months. By checking the transaction, you could choose to approve only the exact amount needed for your trade, mitigating this risk significantly.

Anatomy of a Transaction: The Key Details to Scrutinize

When your wallet prompts you to sign, it’s actually presenting a summary of a data packet. To really understand it, you need to look at the raw details a block explorer provides. Most wallets have a “View Data” or “View on Etherscan” button. Use it. Here’s what to zero in on.

From: The Sender

This one’s easy. This should always be your wallet address. If it’s not, something is very wrong, but this is rarely the point of failure.

To: The Receiver/Contract

This is CRITICAL. Where is this transaction going?

• For a simple transfer (sending ETH to a friend), this will be your friend’s wallet address. Double, no, triple-check it.
• When interacting with a dApp (like swapping on a DEX), this will be the address of the dApp’s smart contract. You need to verify this is the correct, official contract address. Scammers create copycat contracts. Check the project’s official website, Twitter, or Discord for the legitimate address and compare it.

Value: The Amount of Native Currency

This field shows how much of the blockchain’s native currency (ETH on Ethereum, SOL on Solana, etc.) is being sent. If you’re swapping USDC for DAI, this value should be 0 ETH (plus gas). If you’re buying an NFT for 0.5 ETH, it should say 0.5 ETH. If you see a value here when you don’t expect to be sending the native currency, that’s a massive red flag.

Transaction Fee (Gas)

This is the cost to have miners/validators process your transaction. While important for your wallet’s balance, it’s not typically a primary indicator of a scam, though unusually high fees can sometimes be a sign of a complex, potentially malicious contract.

Data: The Heart of the Matter

This is the most technical but most revealing part. It’s a hexadecimal string that tells a smart contract what to do. Thankfully, block explorers do a great job of decoding this for us.

When you look at the transaction details, you’ll often see a field called “Function” or “Method”. This is the decoded version of the ‘Data’ field. It tells you the name of the specific function inside the smart contract you are calling.

• If you are swapping tokens, you should see a function like `swap`, `swapExactTokensForTokens`, or something similar.
• If you are approving a token for a dApp to spend, you’ll see `approve`.
• If you’re minting an NFT, it should say `mint` or `claim`.

This is where you catch the scams. If you think you’re minting an NFT but the function says `setApprovalForAll`, ABORT. That function gives the contract permission to move ALL of your NFTs of a certain type. If you think you’re just signing a message but the function is `transferFrom`, ABORT. You’re about to send your tokens to someone else. Learning to recognize the names of these common functions is your superpower.

Remember: The user interface on a website can lie. The contract code and the function you are calling, as shown on a block explorer, cannot.

Your Pre-Flight Checklist: How to Use Block Explorers to Verify Transactions Step-by-Step

Let’s walk through a common scenario: swapping a token on a decentralized exchange. You’ve gone to the website, entered that you want to swap 100 USDC for some ETH, and your MetaMask pops up.

1. Don’t Sign Yet! Pause. The first and most important step is to resist the urge to immediately click ‘Confirm’.
2. Find the Details. In your wallet prompt, look for a button or tab that says “Data,” “Details,” or “View Transaction”. This will expand the view to show you more information.
3. Go to the Block Explorer. Often, your wallet will have a direct link like “View on Etherscan”. Click it. This will open a new tab showing a *simulation* of your transaction as if it were already completed. This is your playground.
4. Start the Verification Checklist:
   • Check the ‘To’ Address: Does the ‘Interacted With (To)’ address match the official smart contract for the DEX you’re using? Have the official contract address from their documentation or a site like CoinGecko handy to compare it with.
   • Check the ‘Value’: Are you sending any ETH? For a simple token swap, this should be 0 ETH. You’re sending tokens, not the native currency itself.
   • Decode the Function Call: This is the big one. On the Etherscan page, scroll down to the “Input Data” section and click “Decode Input Data”. What function is being called? It should be something like `swapExactTokensForTokens`. You will also see the parameters: the amount of USDC you’re sending (make sure it’s the right amount!) and the minimum amount of ETH you’re willing to receive (a slippage parameter). If it says anything else, especially `approve` (unless it’s your first time) or something unfamiliar, investigate further or reject the transaction.
5. Look at the Token Transfers: The block explorer simulation will also show you a ‘Tokens Transferred’ section. This is a beautiful, plain-English summary. It should clearly show 100 USDC leaving your wallet and a certain amount of WETH (Wrapped ETH) coming into your wallet. If it shows tokens leaving that you didn’t intend to trade, or nothing coming back in return, it’s a scam. Abort mission!
6. Sign or Reject: If everything on the block explorer matches your intent—the right contract, the right function, the right tokens moving—then you can go back to your wallet and confidently click ‘Sign’. If anything looks fishy, click ‘Reject’ without a second thought.

Decoding Smart Contract Interactions is a Non-Negotiable Skill

The process above is the foundation. It gets a little more complex with things like NFT mints or interacting with lending protocols, but the core principles are the same. You’re always checking the destination contract and the function being called.

What about `setApprovalForAll`?

You’ll see this function a lot on NFT marketplaces like OpenSea. It’s a legitimate function that gives the marketplace’s contract permission to move your NFTs on your behalf when you list them for sale. It’s necessary for the platform to work. However, this is the exact same function a scammer will use on a fake website to steal your NFTs. This highlights the absolute importance of verifying that you are interacting with the correct, official smart contract address for OpenSea, Blur, or whatever platform you’re using. If you sign a `setApprovalForAll` transaction on any other contract, you’ve essentially given away the keys to your entire NFT collection of that type.

Beyond Ethereum: A Multi-Chain World

While we’ve used Etherscan as our primary example, this skill is chain-agnostic. The interfaces are remarkably similar across different blockchains, which is great for users.

• Solana: Use Solscan or Solana Explorer. The layout is different, but you can still see the ‘Instruction Details’ which tells you which program (Solana’s version of a smart contract) is being called and what the action is.
• BNB Smart Chain (BSC): BscScan is a clone of Etherscan, so the experience is nearly identical.
• Polygon, Arbitrum, Avalanche, etc.: Most EVM-compatible (Ethereum Virtual Machine) chains have their own Etherscan-like explorer (e.g., PolygonScan, Arbiscan). The verification process is exactly the same.

The key is to make using the appropriate block explorer a reflexive, non-negotiable part of your transaction workflow, no matter which chain you’re on.

Conclusion

In a decentralized world, you are your own bank. That’s incredibly empowering, but it also comes with immense responsibility. There is no customer service line to call if you get scammed. There’s no ‘undo’ button on the blockchain. The tools we have to protect ourselves are knowledge and diligence. Learning to use block explorers to verify transactions is not just a ‘nice to have’ technical skill; it is a fundamental security practice. It’s your shield against the vast majority of scams and exploits targeting crypto users today. It might feel slow and tedious at first, but with practice, it will become a quick, two-minute check that could one day save you from a devastating loss. So, the next time that wallet notification pops up, don’t just sign. Stop, open the block explorer, and verify. Your future self will thank you.

FAQ

What is ‘blind signing’ and why is it dangerous?

Blind signing is the act of approving a transaction in your crypto wallet without fully understanding the underlying data and function being executed. It’s dangerous because malicious websites can display one thing on their user interface (e.g., “Sign In”) while the actual transaction is a command to drain your wallet or grant a scammer permission to spend your tokens. Relying solely on the dApp’s front-end for information is a huge security risk.

Can I use a block explorer for any cryptocurrency?

Yes, virtually every blockchain has its own dedicated block explorer. While Etherscan is for Ethereum and other EVM-compatible chains use similar explorers (like PolygonScan, BscScan), other chains have their own unique ones (like Solscan for Solana or Blockchain.com for Bitcoin). The core concept remains the same: they provide a transparent, searchable record of all transactions on that specific network. The skill of verifying transactions is transferable across chains, though the interface may vary slightly.

The transaction data looks like a bunch of random code. How can I understand it?

While the raw input data is a long hexadecimal string, modern block explorers do most of the heavy lifting for you. Look for a button or link that says “Decode Input Data” or “View as Text”. This will translate the code into a much more readable format, showing you the specific function name (e.g., `transfer`, `swap`, `setApprovalForAll`) and the parameters being used (like the amount and recipient address). Focusing on this decoded information is the key to understanding what the transaction will actually do.