Why pre-screen DeFi engineers before the technical panel
This is one of the few places where a bug is immediately, publicly and irreversibly expensive. Contracts hold funds, the code is readable by anyone, and the incentive to find a flaw is exactly the amount deposited. Engineers worth hiring think like the attacker before the audit does. A short screen asks what they would attack in their own code, which separates them quickly.
What actually matters when screening DeFi Engineer candidates
- 01
Technical proficiency
Check depth in Solidity or Vyper: proxy upgrade patterns, assembly gas optimisation, Foundry or Hardhat test suites, ERC-20/4626 edge cases, and reentrancy or oracle manipulation defences.
- 02
Systems and trade-offs
Probe architecture calls: AMM curve choice, liquidation engine design, oracle selection (Chainlink versus TWAP), L2 versus mainnet deployment, and where they accepted centralisation for safety.
- 03
Evidence and rigour
Test verification habits: fuzz and invariant testing in Foundry, forked mainnet simulations, formal verification with Certora, audit findings received, and post-incident or bug bounty responses.
- 04
Collaboration and communication
Assess work with auditors, protocol governance forums, and DAO contributors: writing specs, snapshot proposals, and explaining contract risk to non-engineering token holders.
Pre-screening questions to ask DeFi Engineer 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.
Protocols they shipped
3 questions01Can you describe a DeFi project you worked on and a problem you had to solve on it?
Listen forA deployed protocol with value held stated, and their specific contribution described in detail.
Projects that never deployed, or a contribution described only as part of a team effort.
02Which DeFi protocols or platforms are you most familiar with?
Listen forReal familiarity with mechanism design, including where a protocol has failed or been exploited.
Protocols named without mechanism detail, or no awareness of major exploits in the ones they cite.
03Can you describe how you have worked with decentralised exchanges in your projects?
Listen forIntegration experience with slippage, price manipulation and oracle dependence all considered in the design.
Exchange prices used directly as an oracle, or manipulation risk not considered in integration.
Security as a habit
3 questions04What approaches do you use for securing decentralised finance applications?
Listen forReentrancy, access control and arithmetic handled by default, with threat modelling before an audit.
Security described as commissioning an audit, or common vulnerability classes not named at all.
05Can you explain the role of smart contracts here and how you have used them?
Listen forUpgrade paths, admin keys and their risks discussed alongside what the contract actually does.
Admin key risk not acknowledged, or upgradeable contracts used without discussing the trust implications.
06What is your experience with Solidity or another contract language?
Listen forFluency including gas cost, storage layout and the language's known sharp edges in production.
Contract code written by tutorial pattern, or gas and storage costs never considered.
Mechanisms understood
4 questions07Could you explain your understanding of liquidity pools and how they operate?
Listen forPool mechanics explained including impermanent loss and how depth affects price impact.
Pools explained as deposits earning yield, or impermanent loss not mentioned or misunderstood.
08Do you have experience with automated market makers?
Listen forCurve design understood, with the arbitrage and manipulation behaviour it produces described.
Market makers described only as a formula, or arbitrage behaviour not understood as part of the design.
09Do you understand over-collateralisation and under-collateralisation?
Listen forCollateral ratios explained with liquidation mechanics and the risk of cascading liquidations.
Collateral treated as a fixed buffer, or liquidation cascades under volatility not considered.
10What is your understanding of how lending and borrowing works in this space?
Listen forInterest models, utilisation and liquidation thresholds all explained together as one interacting system.
Lending described at product level, or the oracle dependence of liquidation not mentioned.
Adversarial testing
2 questions11Do you have experience with blockchain testing tools and frameworks?
Listen forUnit tests plus fork testing and fuzzing, with adversarial cases written rather than happy paths.
Testing limited to expected behaviour, or contracts deployed without testing against forked state.
12How do you handle scalability and transaction cost in this context?
Listen forGas optimisation done without weakening safety checks, with the trade-off stated explicitly.
Safety checks removed to save gas, or cost optimisation prioritised over correctness.
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.
Technical proficiency
35%5Names specific contracts they wrote, explains storage layout and delegatecall risks precisely, and cites gas figures from real deployments.
Systems and trade-offs
25%5Argues trade-offs with economic reasoning, describing MEV exposure, capital efficiency, and admin key or timelock decisions they defended.
Evidence and rigour
25%5Quotes coverage and invariants they wrote, describes an audit finding they disputed or fixed, and shows measured TVL or exploit outcomes.
Collaboration and communication
15%5Points to public governance posts or audit correspondence and explains complex mechanism risk plainly to treasury or community stakeholders.
A bug here is public, irreversible and priced at the amount deposited. A one-way video screen asks what they would attack.
Try it on HirevireScreening FAQ
Process basics
How long should a pre-screening round for this role take?
Fifteen minutes across eight to ten questions, answered async. Enough to establish protocols they shipped, test security thinking, and check their grasp of the economic mechanisms.
Should the screen replace a code review?
No. It filters before you spend senior engineering time reading contracts. Always follow with a review of deployed code they wrote, since everything in this field is publicly verifiable.
Evaluating answers
What is the strongest signal when screening this role?
What they would attack in their own code. Engineers who ship safely name specific weaknesses. Anyone who says an audit covered it has outsourced the thinking that matters most.
What should worry me in an answer?
Treating an audit as the security plan. Audits catch a portion of issues within a time box, and an engineer relying on that will ship the classes of bug audits routinely miss.
Go deeper on this role
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
