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  • How to Explain External Call Risks in Solidity Interviews?

    Synthill Brown

    Member

    Updated: May 8, 2025
    Views: 1.7K

    What are the risks of using external calls in smart contracts, and how do you mitigate them?
    That was the question I got during a recent Solidity developer interview.

    I mentioned the common issues—reentrancy attacks, gas inefficiency, and dependency on the reliability of external contracts. But now I’m thinking: did I miss any critical angles?

    If you've faced this question in interviews, how did you approach it? Any structure or specific points that helped you stand out? I’m fine-tuning my answer and would really appreciate insights from those who've been there.

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  • Varun Mehta

    Member • 3mos

    Interviewers ask about external calls in Solidity to test security knowledge. Focus on reentrancy, unexpected control flow, and gas issues. A strong answer explains these risks and how to prevent them.

    External calls in Solidity allow interactions with other contracts but introduce security risks. The biggest risk is reentrancy, where an attacker repeatedly calls back into the contract before the first call completes. Prevent this using the checks-effects-interactions pattern—update state variables before making external calls. Another issue is unexpected control flow, where an external contract executes arbitrary code. Use pull payments instead of direct transfers to reduce this risk. Gas issues also matter; external calls may fail if the target contract runs out of gas. Avoid fixed gas stipends and use try-catch blocks to handle failures safely. Keeping external calls minimal and verifying contract addresses before interaction adds security.

    This structured response covers risks and mitigation clearly, making it easy to understand.

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  • Shubhada Pande

    Community Administrator • 1w

    For more Solidity questions, read our blog https://artofblockchain.club/article/top-30-interview-questions-for-senior-solidity-developers-in-2025

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