Okay, so check this out — I was debugging a token transfer last week and hit a weird failure that only showed up off‑chain. Wow. My first guess was gas or a reentrancy guard, but that felt off. My instinct said: open the block explorer and stare at the raw events. That’s where the story started.
I’ve been poking around Ethereum transactions since the early days. I’ve watched tokens launch, rug pulls crumble, and NFT metadata rot when IPFS links vanished. I’ll be honest: the tools get better, but the problems evolve. This piece is about practical workflows for ERC‑20 tokens and NFTs, what to look for, and a few traps that still trip people up. It’s rooted in real debugging sessions, not theory. Some bits are opinionated — I’m biased toward transparency and verifiable source code.
Quick preface — if you want a straightforward transaction or contract lookup, the explorer I reach for most is etherscan. It’s not perfect, but it’s the utility belt I use when things get weird.
Start with the Transaction
When an ERC‑20 transfer looks wrong, the transaction page is your first stop. Look at the status, gas used, and the input data. You can decode input with the contract’s ABI if the source is verified. Seriously — verified source code is a lifesaver. If it’s not verified, you’re flying blind.
Check the event logs. Events are what tell you whether Transfer or Approval events emitted as expected. On one occasion, a token contract emitted Transfer events but balances didn’t match because the contract used a nonstandard internal bookkeeping method. On the one hand that’s crafty; on the other, it’s a UX nightmare.
Also watch for proxy patterns. Many tokens are proxies, so the contract address you see might be a dispatcher. Click through to the implementation contract. It changes how you reason about upgrades and ownership.
ERC‑20 Specifics: Common Things to Inspect
Here’s a checklist I run through fast — like muscle memory:
- Is the token’s contract source verified? If yes, read the code. If no, be cautious.
- Are Transfer events indexed properly? Missing indexes mean you might miss holders in some tools.
- Look at allowances. Over-permissioned approvals are a major vector for token theft.
- Check totalSupply vs. sum of balances. Mismatches can indicate hidden minting functions.
- Find owner or admin roles. Can they mint or pause? If yes, that affects risk profile.
One time I found a token with a public mint function gated only by block.timestamp — cute but exploitable. On the surface, the token looked standard; under the hood? Not so much. Something about that still bugs me.
NFTs: TokenURI, Metadata, and Who Holds What
NFTs are a different animal. The tokenURI can point to IPFS, Arweave, or a centralized URL. If the metadata is centralized, expect surprises. Metadata mutability is common: projects change art, update properties, or replace metadata endpoints. That’s fine if the team is transparent; it’s not if changes are opaque.
When tracking an NFT transfer or sale, check the ERC‑721/1155 Transfer events, then inspect the tokenURI contract call. If the tokenURI returns an IPFS hash, try fetching it directly. If it’s a JSON object that points to another URL, dig deeper. For marketplaces, make sure marketplace contracts have proper approvals and that royalties are enforced off‑chain if needed.
Contract Verification and Reading State
Verifying the contract source is the single best signal of legitimacy. If the code is verified, you can:
- Read public variables (owner, cap, paused)
- Call view functions directly from the explorer
- Trace logic paths for minting, burning, or transfers
If verification is missing, you can still look at bytecode, but that’s for deep divers. Initially I thought bytecode-only meant “not legit,” but actually, some teams delay verification for deployment speed. Still—lack of verification reduces trust.
Using the Explorer’s API and Event Indexing
For devs building dashboards, the explorer’s APIs and indexed events are invaluable. You can pull token holder lists, transfers, and contract source info programatically. Caveat: indexing lags and event naming inconsistencies can cause weird edge cases. Build fallback logic.
Pro tip: monitor Transfer events and watch for large holder concentration. Token distribution matters. If a few wallets hold most supply and have transferability, consider the dump risk.
Scams, Approvals, and Common Attack Patterns
Okay, serious bit. The majority of token-related losses come from approvals and social-engineered signatures. Approve() gives a spender access to move tokens — treat it like handing over your wallet temporarily. Revoke approvals when you’re done. Many explorers expose an approval checker; use it.
Also watch for tokens that implement bizarre fee-on-transfer logic. Those can break aggregators and swaps. And watch for tokens that require a function call to “activate” transfers. They exist, and they surprise people.
Practical Workflow — What I Do, Step by Step
Here’s a short workflow I run during an incident:
- Open the tx in the explorer, note status and gas usage.
- Decode input; locate the contract and check verification.
- Inspect Transfer/Approval events; cross‑check balances.
- Check token holder distribution and recent large transfers.
- For NFTs: fetch tokenURI and verify metadata source.
- If needed, use the API to pull a sequence of events for timeline analysis.
It’s simple but reliable. I learned it from repeated mistakes and a few panicked nights. Something felt off every time I skipped a step.
FAQ — Real Questions I Get All The Time
How can I tell if a token is a scam?
Look for red flags: unverifed source code, centralized mint/pause functions, extremely skewed holder distribution, and developer wallets labeled anonymously. Also check if token transfers are being restricted or if the contract has owner-only transfer privileges.
Why is a Transfer event present but balances don’t add up?
Some contracts use internal ledger updates that aren’t standard ERC‑20, or they might emit events while actually reverting state under certain conditions. Always read the verified code or query public view functions to confirm true balances.
Can explorers show historical metadata for NFTs?
Not always. Explorers will show the current tokenURI and often cache metadata, but if a project changed its metadata endpoint, you may need archive services (like the Wayback Machine) or IPFS history to reconstruct previous states.
Look — blockchain explorers aren’t magic, but they’re the forensic microscope for on‑chain behavior. If you treat them like a trusted assistant and combine them with skepticism, you’ll avoid a lot of common traps. I’m not 100% sure about every edge case — nobody is — but a practical, code‑reading mindset gets you farther than blind trust.
Keep your approvals tight, verify contract source code, and when in doubt, dig into the events. Oh, and check transaction receipts carefully — that tiny “gas used” difference has saved me more than once.
