Understanding the ABI — Plain-language primer

What the ABI isThe ABI (Application Binary Interface) describes how to call functions and read events on a contract: names, types, order, and mutability. Wallets, SDKs, and explorers rely on it to build calldata, decode logs, and render UIs.

Selectors and calldataEvery external call starts with a 4-byte selector (keccak of the function signature) followed by encoded arguments. If the selector is wrong or the encoding mismatches types, the call reverts or hits fallback.

EventsABIs also define event signatures and parameter types used to decode logs (topics + data). Changing event shapes breaks dashboards and indexers.