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Blockchain Developer

Practice Blockchain Developer questions on Solidity, the EVM, gas, smart contract security, tokens, Layer 2s and dApp design.

Questions: 100
Interview Qs: 30
Judged problems: 39
Skills: 9

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About the role

A Blockchain Developer builds smart contracts and the applications around them. Most work today happens on Ethereum and EVM-compatible chains such as Arbitrum, Optimism, Base and Polygon, using Solidity, with other ecosystems like Solana (Rust) also popular. A typical day includes writing and testing contracts with Foundry or Hardhat, reviewing code for security issues, optimising gas costs, and connecting a frontend to contracts with libraries like viem, ethers.js and wagmi.

The job is different from normal backend work because deployed contracts are public, often hold real money, and are hard to change. A single bug can be exploited within minutes and cannot be rolled back. So you spend a lot of time on testing, fuzzing, careful design, audits and understanding attack patterns like reentrancy, oracle manipulation and access control mistakes.

As you grow, you design protocol architecture, upgrade strategies and token economics, work with auditors, and build systems that span multiple chains and Layer 2 networks.

Practise by level

easy

Easy challenges

34 questions

medium

Medium challenges

34 questions

hard

Hard challenges

32 questions

Open the full question bank (100 questions) →

Mock interview

easy

Screening round

4 questions · 4 min each · pass 50%

medium

Technical round

5 questions · 4 min each · pass 60%

hard

Final round

6 questions · 3 min each · pass 70%

Coding problems for blockchain developers

All 39 problems →

Skills in this track

Gas Upgradeability Cryptography Tokens Solidity Blockchain Fundamentals EVM Fundamentals Smart Contract Security Gas Optimisation Token Standards Dapp Frontend Deployment Testing And Fuzzing Foundry Layer 2 Security DEFI Testing Openzeppelin

Learning roadmap

1
Blockchain fundamentals
Learn how blocks, transactions, hashing, public-key cryptography, consensus (proof of stake) and accounts work. Understand wallets, gas and transaction fees.
2
Solidity and the EVM
Learn Solidity types, storage vs memory vs calldata, events, modifiers, errors, inheritance and how the EVM executes code and charges gas.
3
Tools and testing
Use Foundry or Hardhat to compile, test, fuzz and deploy. Write unit, fuzz and invariant tests, and fork mainnet for realistic testing.
4
Security
Study reentrancy, access control, integer issues, oracle manipulation, front-running and signature replay. Use OpenZeppelin libraries, Slither and audit reports.
5
Standards and DeFi patterns
Implement ERC-20, ERC-721 and ERC-4626 vaults, learn AMMs, lending, proxies and upgradeability, and account abstraction (ERC-4337).
6
Full-stack dApps and scaling
Connect frontends with viem and wagmi, index events with The Graph or custom indexers, and deploy to Layer 2 rollups with bridges and cross-chain messaging.