> ## 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.

# EXTCODECOPY (0x3c)

> Copy external account's code to memory

<Warning>
  **This page is a placeholder.** All examples on this page are currently AI-generated and are not correct. This documentation will be completed in the future with accurate, tested examples.
</Warning>

## Overview

**Opcode:** `0x3c`
**Introduced:** Frontier (EVM genesis)

EXTCODECOPY copies bytecode from an external account into memory.

## Specification

**Stack Input:**

```
address (uint160 as uint256)
destOffset (memory offset)
offset (code offset)
length (bytes to copy)
```

**Stack Output:**

```
[]
```

**Gas Cost:** 700 (access) + 3 + memory expansion + (length / 32) \* 3

## Behavior

Copies `length` bytes from external account's code at `offset` to memory at `destOffset`. Zero-pads if code bounds exceeded.

## Examples

### Copy Contract Code

```solidity theme={null}
function getExternalCode(address account) public view returns (bytes memory code) {
    assembly {
        let size := extcodesize(account)
        code := mload(0x40)
        mstore(code, size)
        extcodecopy(account, add(code, 0x20), 0, size)
        mstore(0x40, add(add(code, 0x20), size))
    }
}
```

### Verify Implementation

```solidity theme={null}
function verifyCode(address account, bytes32 expectedHash) public view returns (bool) {
    bytes memory code;
    assembly {
        let size := extcodesize(account)
        code := mload(0x40)
        extcodecopy(account, add(code, 0x20), 0, size)
    }
    return keccak256(code) == expectedHash;
}
```

## Gas Cost

**Base:** 700 gas (Tangerine Whistle+)
**Memory expansion:** Variable
**Copy cost:** 3 gas per word

**Berlin+:** 2600 (cold) / 100 (warm) + memory + copy

## Common Usage

### Clone Factory

```solidity theme={null}
function clone(address implementation) internal returns (address instance) {
    bytes memory code;
    assembly {
        let size := extcodesize(implementation)
        code := mload(0x40)
        extcodecopy(implementation, add(code, 0x20), 0, size)
    }
    // Deploy cloned code
}
```

## Implementation

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    export function extcodecopy(
      frame: FrameType,
      host: BrandedHost
    ): EvmError | null {
      // Pop address, destOffset, offset, size
      // Calculate gas costs
      // Copy external code to memory
      // See full implementation in codebase

      frame.pc += 1;
      return null;
    }
    ```
  </Tab>
</Tabs>

## References

* [Yellow Paper](https://ethereum.github.io/yellowpaper/paper.pdf) - Section 9.1
* [EVM Codes - EXTCODECOPY](https://www.evm.codes/#3c)
* [EIP-150](https://eips.ethereum.org/EIPS/eip-150)
* [EIP-2929](https://eips.ethereum.org/EIPS/eip-2929)