# ABIs & Contracts

## Overview

The [Application Binary Interface (ABI)](https://docs.soliditylang.org/en/latest/abi-spec.html)
defines how data is encoded and decoded between your application and a contract's bytecode. Ox
provides a module for each ABI item type — [`Abi`](/api/Abi), [`AbiFunction`](/api/AbiFunction),
[`AbiEvent`](/api/AbiEvent), [`AbiError`](/api/AbiError), and
[`AbiConstructor`](/api/AbiConstructor) — covering everything between your app and the contract:
parsing ABIs, encoding calls, and decoding what comes back. Recipes end at the encoded payload;
hand it to a JSON-RPC transport, or use a higher-level client like [Viem](https://viem.sh) for
full contract workflows.

```ts twoslash
import { Abi, AbiFunction } from 'ox'

const abi = Abi.from([
  'function approve(address spender, uint256 amount) returns (bool)',
  'event Transfer(address indexed from, address indexed to, uint256 amount)',
])

const approve = AbiFunction.fromAbi(abi, 'approve')

const data = AbiFunction.encodeData(approve, [
  '0xcb98643b8786950f0461f3b0edf99d88f274574d',
  100_000_000n,
])
// @log: '0x095ea7b3000000000000000000000000cb98643b8786950f0461f3b0edf99d88f274574d0000000000000000000000000000000000000000000000000000000005f5e100'
```

<Cards>
  <Card icon="lucide:rocket" title="Deploy Contracts & Compute Addresses" description="Encode constructor calldata and precompute CREATE and CREATE2 addresses." to="/guides/abi/deployment" />

  <Card icon="lucide:file-code-2" title="Work with ABIs" description="Parse, format, and inspect ABIs, items, parameters, and selectors." to="/guides/abi/abis" />

  <Card icon="lucide:radio" title="Work with Events & Logs" description="Filter logs by topic and decode indexed and non-indexed arguments." to="/guides/abi/events" />

  <Card icon="lucide:binary" title="Work with Function Calls" description="Encode calldata for reads and writes, and decode results and inputs." to="/guides/abi/function-calls" />

  <Card icon="lucide:circle-alert" title="Work with Reverts & Custom Errors" description="Turn revert data into typed errors, reasons, and panic codes." to="/guides/abi/errors" />
</Cards>