> ## Documentation Index
> Fetch the complete documentation index at: https://voltaire.tevm.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Abi.decodeData

> Decode function calldata by selector

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## Overview

`Abi.decodeData` inspects calldata, matches the selector to a function in your ABI, and decodes the arguments. Use this when you have raw transaction calldata and want to recover the called function and parameters.

## Quick Start

```typescript theme={null}
import { Abi } from '@tevm/voltaire/Abi';
import { Hex } from '@tevm/voltaire/Hex';

const abi = Abi([
  {
    type: 'function',
    name: 'transfer',
    stateMutability: 'nonpayable',
    inputs: [
      { type: 'address', name: 'to' },
      { type: 'uint256', name: 'amount' }
    ],
    outputs: [{ type: 'bool' }]
  }
] as const);

const calldata = Hex.toBytes(
  '0xa9059cbb000000000000000000000000742d35cc6634c0532925a3b844bc9e7595f51e3e' +
  '00000000000000000000000000000000000000000000000000000000000003e8'
);

const decoded = abi.decodeData(calldata);
// { functionName: 'transfer', args: ['0x742d35...', 1000n] }
```

## Unknown Selectors

If the selector does not match any function in the ABI, `Abi.decodeData` throws `AbiItemNotFoundError`.

```typescript theme={null}
import { Abi, AbiItemNotFoundError, AbiInvalidSelectorError } from '@tevm/voltaire/Abi';

try {
  abi.decodeData(calldata);
} catch (error) {
  if (error instanceof AbiInvalidSelectorError) {
    console.error('Calldata too short to contain a selector');
  }
  if (error instanceof AbiItemNotFoundError) {
    console.error('Unknown function selector');
  }
}
```

## Decode Parameters Without Selector

If you already know the function and only have parameters (no selector), decode with `Abi.Function.decodeParams` or `Abi.decodeParameters`:

```typescript theme={null}
const transferFn = abi.getFunction('transfer');
const args = Abi.Function.decodeParams(transferFn, calldata);
// or
const params = Abi.decodeParameters(transferFn.inputs, calldata.slice(4));
```

## See Also

* [decode](/primitives/abi/decode) - Decode function return values
* [Function.decodeParams](/primitives/abi/function-decode-params) - Decode calldata for a known function
* [Encoding](/primitives/abi/encoding) - ABI encoding rules