web3.js is a developer library for Web3 applications, RPC access, contracts, and wallet workflows. It helps Web3 teams work with blockchain applications, smart contracts, wallets, data, and onchain infrastructure using a focused product or developer workflow.

Use it for:

• Build typed blockchain integrations.
• Read chain state through RPC providers.
• Send transactions and call smart contracts.
• Create scripts, backends, and application libraries.

Best fit: developers building application logic close to the chain.