ETH Cluj 2026: How To Build on Arbitrum

Welcome to the ETH Cluj 2026 workshop materials. This book covers everything from Ethereum fundamentals and Arbitrum’s role in the ecosystem, through writing your first Solidity smart contract, deep-diving into Stylus and WebAssembly, to building a full-stack dApp frontend.

Important Links

• Telegram group for questions

• Metamask wallet

• Chainlist — add Superposition testnet

• Superposition faucet

• Superposition testnet explorer

• Remix browser Solidity editor

• Wizard Stylus editor

• Stackblitz full-stack editor

• Wagmi React hooks docs

• GitHub repository

Note

The contract code in this book was not written with ERC20 safety in mind. There are no return value checks. Not for production!

Table of Contents

• 1. Arbitrum’s role in the Ethereum roadmap
• 2. Your First Smart Contract on Arbitrum
• 3. Stylus for beginners
• 4. Introducing our fake blockchain
  • 4.1. Public-private key cryptography
  • 4.2. What are transactions?
  • 4.3. How can we have programmability on our blockchain?
• 5. Introducing a real blockchain (Arbitrum)
  • 5.1. How does Arbitrum work?
  • 5.2. Accounts
• 6. How does Arbitrum execute code?
  • 6.1. What’s Webassembly (WASM)?
  • 6.2. Why?
  • 6.3. How is WASM run on-chain?
  • 6.4. How does WASM differ from the stack machine we showed off before?
  • 6.5. WASM echo contract example
  • 6.6. WASM example making use of storage
  • 6.7. WASM example calling other code
• 7. Recapping everything
• 8. Deploy & Go - From Contract to App

Appendices

• Stylus Challenges