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

# Simple Vault Contract

> A basic DeFi vault that accepts ETH deposits and allows withdrawals.

# Simple Vault Contract

A basic DeFi vault that accepts ETH deposits and allows withdrawals.

A basic DeFi vault that accepts ETH deposits and allows withdrawals.

## Explanation

This vault demonstrates core DeFi primitives: deposit, withdraw, and balance tracking.

**Security notes:**

* Uses the **checks-effects-interactions** pattern: state is updated *before* the external call.
* `msg.sender.call{value: amount}` sends ETH safely (vs. `transfer` which has gas limits).
* Always validate amounts with `require` before state changes.

In production, add reentrancy guards, events, and proper access controls.

## Code

```solidity theme={null}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract SimpleVault {
    mapping(address => uint256) public balances;

    function deposit() external payable {
        require(msg.value > 0, "Must send ETH");
        balances[msg.sender] += msg.value;
    }

    function withdraw(uint256 amount) external {
        require(balances[msg.sender] >= amount, "Insufficient balance");
        balances[msg.sender] -= amount;
        (bool success, ) = msg.sender.call{value: amount}("");
        require(success, "Transfer failed");
    }

    function getBalance() external view returns (uint256) {
        return balances[msg.sender];
    }
}
```

***

**Canonical knowledge ID:** `code-example:simple-vault-contract`