Top Solidity interview questions and answers in 2023

If you want to work as a successful Solidity developer in a top Silicon Valley company or build a team of brilliant Solidity developers, you've come to the right place. We have carefully prepared a list of Solidity developer interview questions for your Solidity interview to give you an idea of the type of Solidity interview questions you can ask or be asked.

Last updated on Sep 6, 2022

In the field of development, Solidity developers are in great demand. This demand creates stiff competition for Solidity developers. Hence, the technical Solidity interview questions aren't exactly easy to crack. If you are a Solidity developer looking for a job or a recruiter looking for the best Solidity developer, the list of Solidity interview questions and answers below can help. You can use it to model other Solidity interview questions based on this pattern or answer similar technical Solidity interview questions.

Solidity interview questions and answers


Is it accurate that private variables are truly private?

This is one of the most popular Solidity interview questions. The answer is No. Only the EVM has access to private information (Ethereum Virtual Machine, the part of Ethereum that executes smart contracts). On the other hand, smart contract data is stored on the Ethereum blockchain, which is open to the world. Anyone can read secret variables of smart contracts using a particular tool for analyzing blockchain data.


What is a smart contract's ABI?

The ABI specifies a smart contract's interface or the set of functions that may be accessed from outside of the smart contract. Only the function signatures (function names, argument types, and return types) are defined by the ABI, not their implementation. The contract's events are likewise defined by the ABI. The ABI is used by Ethereum client libraries like web3 to interface with the smart contract outside of the smart contract.


What is the equivalent of a Javascript console.log in Solidity for debugging?

This question is often a part of the Solidity developer interview questions. In Solidity, there is no comparison; however, you can use events, even if they aren't built for this.


How can you protect yourself from a re-entry attack?

You will frequently come across this Solidity developer interview question.

Solution 1: Lower balances and update other state variables before invoking the other contract. Solution 2: Implement a re-entrancy guard that uses a variable to determine when a call is second in the stack. Solution 3: Limit the amount of gas available to the called contract. This is automatically done if you use transfer().


What are the two APIs that a smart contract uses to interface with it?

This is one of the most popular Solidity interview questions. eth_sendTransaction (transaction) and eth_call (call) are the two APIs that are used by a smart contract to interface. Transactions are expensive (gas) and can change the blockchain. Calls don't cost anything; therefore, they can't change the blockchain. However, calls can return a value, which isn't the case with transactions.


What is the method of payment for gas?

Gas is paid in ether using the formula: ether cost = gasPrice * gas. In this formula, the gas represents the gas cost of executing a transaction. gasPrice is in wei / gas, usually expressed in Gwei. A transaction also shows a gasLimit parameter- it specifies the maximum number of gas that a transaction can pay. A transaction without this could potentially deplete an account's Ether.


What are the requirements for deploying a smart contract on the Ethereum network?

  • A bytecode of smart contract
  • An Ethereum address with sufficient Ether
  • A wallet to sign the transaction
  • A tool to create the transaction and coordinate the signing process with the wallet


What exactly is EVM bytecode?

This is one of the most popular Solidity interview questions. EVM bytecode is a low-level programming language that is compiled from a high-level programming language like Solidity. EVM is a virtual machine that sits between the operating system and the application layer to reduce OS dependency. Ethereum smart contracts, thanks to EVM, can be run on nearly any computer. The EVM bytecode comprises opcodes, which are EVM elementary instructions. These opcodes define basic operations such as adding two numbers (ADD), loading data from memory (mload), and so on. The Ethereum yellow paper defines over 100 of these opcodes. We need higher languages like Solidity to help us reason at a higher level of abstraction because coding directly using opcodes would be incredibly tiresome.


Is it feasible to send a transaction without having to charge customers for gas?

You’ll often find this question among the Solidity developer interview questions, and the answer is Yes. You'd have people sign a message on the front end first. The message and signature would then be routed to a centralized backend (off-chain) that would establish a transaction and include the payload (message + signature). This means that instead of the user's wallet, the app's wallet will cover gas costs. A smart contract will validate the signature's validity and perform an activity on behalf of the user on the blockchain.


What is a library and how many types are there?

A library is a piece of code that other smart contracts can re-use. There are 2 types of libraries:

  • Deployed- They have their own address, and several other smart contracts can use them.
  • Embedded- They don’t have their own address and are deployed as part of the code of the smart contract that uses them.

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Wrapping up

A Solidity developer’s interview procedure doesn’t stop at technical Solidity interview questions. As a candidate seeking a dream Solidity developer job, you must be prepared to answer Solidity interview questions and questions about your soft skills, such as communication, problem-solving, project management, crisis management, team management, and so on. It is your duty as a recruiter to identify a Solidity developer who fits your company's culture. As a result, besides technical Solidity interview questions, you should also inquire about the candidates' team and social skills.

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