Pre-Screening Interview Questions to Ask a Smart Contract Developer

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Sanat Hegde
Sanat Hegde · Founder, Hirevire
Founder of Hirevire, screening software used by 500+ companies

Smart contract bugs are permanent and expensive in a way ordinary software bugs are not. These questions separate developers who write with an adversary in mind from those who write code that works.

TL;DR, what to screen for

The best pre-screening questions for a smart contract developer test four things: contracts they deployed that hold real value, whether they think about an attacker rather than a user, whether testing goes beyond the happy path to invariants and forked state, and whether they understand what upgradeability actually costs. Ask about an exploit. Familiarity with them is a qualification here.

  • Contracts holding value
  • Thinking like an attacker
  • Testing past happy path
  • Upgrades and their cost

Why pre-screen smart contract developers before the technical interview

A deployed contract is code you cannot patch, running where anyone can call it, holding funds an attacker is paid to take. Ordinary competent software engineering is not sufficient, and the difference shows up as a total loss rather than a bug report. Developers worth hiring can walk through classes of exploit and say which ones their own code was reviewed against. A short screen finds out whether someone writes with an adversary in mind.

What actually matters when screening Smart Contract Developer candidates

  1. 01

    Technical proficiency

    Check Solidity or Rust depth: storage packing, proxy upgrade patterns (UUPS, transparent), reentrancy guards, assembly use, and testing in Foundry, Hardhat or Anchor.

  2. 02

    Systems and trade-offs

    Probe gas optimisation trade-offs, on-chain versus off-chain logic, oracle choice (Chainlink, Pyth), L2 selection, and how upgradeability was balanced against trust minimisation.

  3. 03

    Evidence and rigour

    Test how they verify correctness: unit and fork tests, fuzzing, Slither or Echidna runs, formal methods, and response to audit findings before mainnet deployment.

  4. 04

    Collaboration and communication

    Assess work with auditors, protocol economists and frontend teams: NatSpec docs, ABI handoffs, incident comms during exploits, and governance proposal write-ups.

Pre-screening questions to ask Smart Contract Developer candidates

12 questions grouped by what they test. Ask the same set in every screen and score answers on a consistent scale, or send them as an async video screen and compare answers side by side.

Contracts holding value

4 questions

  1. 01What types of smart contracts have you developed in the past?

    Listen for

    Deployed contracts with addresses available, and a clear split between what they wrote and what they forked.

    Only testnet deployments, or forked contracts presented as their own work.

  2. 02Can you describe a project where you implemented a decentralised application?

    Listen for

    The full application including how state is read and how the interface handles a failed or pending transaction.

    Contract work with no understanding of how users actually interact with it, or failure states never handled.

  3. 03Have you developed any decentralised finance projects?

    Listen for

    Value handled with the economic attack surface considered, including oracle dependence and price manipulation.

    Financial logic written with no thought about manipulation, or oracles trusted without validation.

  4. 04Do you have any experience with upgradeable smart contracts?

    Listen for

    The trust trade-off stated plainly, with storage layout risks understood and who controls the upgrade named.

    Upgradeability added by default, or an upgrade key held by one person with no timelock.

Thinking like an attacker

3 questions

  1. 05Have you ever dealt with a smart contract security breach? How did you detect and handle it?

    Listen for

    A real incident or a close study of one, with detection, response and what changed in their practice afterwards.

    No familiarity with real incidents in this field, or a breach described with no lesson taken from it.

  2. 06Can you discuss your methodology for auditing smart contracts for security vulnerabilities?

    Listen for

    Named vulnerability classes checked systematically, with a finding they made in someone else's code.

    Auditing described as running a static analysis tool, or reliance on an external audit as the only check.

  3. 07Tell us about your ability to write clean, secure code that can scale with requirements.

    Listen for

    Gas cost treated as a design constraint alongside clarity, with a specific optimisation and what it cost in readability.

    Gas never considered, or optimisation pursued to the point where the code cannot be reviewed.

Testing past happy path

2 questions

  1. 08Do you have practical experience with smart contract testing tools?

    Listen for

    Invariant testing and fuzzing used alongside unit tests, with a bug that only surfaced under adversarial inputs.

    Tests that only confirm intended behaviour, or coverage claimed with no hostile cases.

  2. 09Please discuss your knowledge of common blockchain development frameworks and tooling.

    Listen for

    Tooling used daily including forked mainnet testing against real protocol state rather than mocked contracts.

    Testing only against mocks, or tooling named with no workflow described around it.

Upgrades and their cost

3 questions

  1. 10What blockchain platforms are you familiar with as a smart contract developer?

    Listen for

    Depth on one platform with an honest view of what differs elsewhere, rather than every chain claimed equally.

    Many chains listed with shallow experience, or no awareness of how execution differs between them.

  2. 11Do you have any experience with layer two scaling solutions?

    Listen for

    A working view on the trust and withdrawal trade-offs, drawn from something they deployed rather than read about.

    Scaling solutions described as faster and cheaper with no mention of the trade-offs they carry.

  3. 12Can you discuss your understanding of consensus algorithms and blockchain governance?

    Listen for

    Enough grounding to reason about finality and reorganisation risk, with governance treated as a real attack surface.

    Consensus described from documentation only, or governance mechanisms designed with no capture risk considered.

How to score responses

Score every candidate on the same four criteria immediately after the screen. At this stage you are shortlisting for panel interviews, not making the final call.

  1. Technical proficiency

    35%

    5Names specific EVM quirks, writes invariant tests in Foundry, and explains delegatecall storage collisions from real code they wrote.

  2. Systems and trade-offs

    25%

    5Justifies architecture with gas numbers and threat assumptions, and can defend when immutability beat an upgrade path.

  3. Evidence and rigour

    25%

    5Cites coverage figures, fuzz campaigns, and specific audit findings they triaged, disputed or fixed with a follow-up commit.

  4. Collaboration and communication

    15%

    5Describes clear handoffs and a post-incident or postmortem write-up others acted on, without blaming external contributors.

A deployed contract cannot be patched and an attacker is paid to break it. A one-way video screen asks what they deployed and what it was checked against.

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Screening FAQ

Process basics

How long should a pre-screening round for a smart contract developer take?

Fifteen minutes across eight to ten questions, answered async, with deployed addresses. Enough to establish what holds real value, test their security thinking, and hear how they test beyond the happy path.

Should I ask for deployed contract addresses?

Yes. The code is public, so a contract address is verifiable evidence in a way a repository link is not. Ask what they wrote versus forked, and whether it was audited before or after deployment.

Evaluating answers

What is the strongest signal when screening a smart contract developer?

How they discuss exploits. Strong candidates name classes of attack and describe how their own code was checked against each. Anyone who has not studied real incidents in this field is going to reproduce one.

How do I judge testing answers?

Ask what they test beyond the intended path. Real answers cover invariants, fuzzing and forked mainnet state with hostile inputs. Anyone whose tests only confirm the feature works has not tested the thing that matters.

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Sanat Hegde
Sanat Hegde
Founder, Hirevire

Sanat has been hiring since 2012 and watching the recruitment industry change up close ever since, and turned that screening process into Hirevire's video screening platform. LinkedIn

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