How do you explain reentrancy in interviews without sounding like you memorized it?

Emma T · 2025-10-27T11:42:54+00:00

I keep practicing smart contract interview questions, and reentrancy comes up every time.I can say the rule: “Do Checks-Effects-Interactions.”But when they ask why the order matters, I struggle to explain the actual risk.How does the attacker still use their old balance?Why does the whole contract state not update in time?And what exactly makes Pull payments safer than Push payments when money is on the line?I don’t want to recite textbook lines and sound like a junior who’s just memorizing stuff.I want to understand how seniors think about reentrancy so I can explain it confidently in interviews.If anyone has a moment where this finally clicked for them (test, diagram, code review), please share 🙏Your experience might help a lot of us preparing for Solidity roles.

How do you explain reentrancy in interviews without sounding like you memorized it?

Emma T
@5INFFa4

Updated: Oct 30, 2025

Views: 105

I keep practicing smart contract interview questions, and reentrancy comes up every time.
I can say the rule: “Do Checks-Effects-Interactions.”
But when they ask why the order matters, I struggle to explain the actual risk.
How does the attacker still use their old balance?
Why does the whole contract state not update in time?
And what exactly makes Pull payments safer than Push payments when money is on the line?
I don’t want to recite textbook lines and sound like a junior who’s just memorizing stuff.
I want to understand how seniors think about reentrancy so I can explain it confidently in interviews.
If anyone has a moment where this finally clicked for them (test, diagram, code review), please share 🙏
Your experience might help a lot of us preparing for Solidity roles.

2

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ChainMentorNaina

@ChainMentorNaina • 3w

I only understood reentrancy when I stepped through state in the debugger. Funds left the contract but storage didn’t update yet — so attacker reused their old balance. That’s when I realized CEI isn’t a pattern. It’s preventing lies in the system during external calls. Tip for interviews: mention “timing gap between state + effects.”

Abdil Hamid

@ForensicBlockSmith • 2w

My first testnet deployment got reentered because I updated balances late. Funds drained. Brutal day. But now in interviews when they ask “Why CEI?” I can answer: “Because users shouldn’t influence system state before it’s locked in.” Experience becomes confidence.

Shubhada Pande

@ShubhadaJP • 2w

This is a really thoughtful discussion — and it highlights something many candidates miss during interviews. When teams ask about reentrancy, they’re not just testing if you can explain “how” it happens. They’re quietly assessing whether you understand risk ownership — how you think when value moves across contracts, and how predictable your approach is under pressure.

Founders and auditors often treat this as a signal of mindset rather than memorization. A developer who explains the why behind checks and control flow automatically builds more trust than someone reciting CEI steps.

We had a related breakdown on how interviewers frame external call vulnerabilities → https://artofblockchain.club/discussion/best-way-to-answer-risks-of-external-calls-in-solidity-developer-interviews

and a practical piece on how smart contract audits build long-term trust → https://artofblockchain.club/article/smart-contract-audits-your-codes-essential-security-check Both connect well with what this thread is exploring.

Akemi R

@snappy-bullet • 2w

Tis is a much needed info................i also struggle with this "gas" questions.