web3-smart-contracts

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Web3 Smart Contracts

Web3智能合约

Smart contract development on EVM-compatible blockchains requires a unique discipline - code is immutable once deployed, bugs can drain millions, and every computation costs gas. This skill covers Solidity best practices, security-first development, DeFi protocol patterns, gas optimization, and audit-grade code review. It equips an agent to write, review, and audit smart contracts the way a professional auditor at Trail of Bits or OpenZeppelin would approach the task.

在兼容EVM的区块链上开发智能合约需要遵循独特的准则——代码部署后不可更改，漏洞可能导致数百万资金损失，且每一次计算都要消耗Gas。此技能涵盖Solidity最佳实践、安全优先的开发方式、DeFi协议模式、Gas优化以及审计级别的代码评审。它能让Agent以Trail of Bits或OpenZeppelin专业审计人员的方式来编写、评审和审计智能合约。

When to use this skill

何时使用此技能

Trigger this skill when the user:

Writes or reviews Solidity smart contracts
Asks about smart contract security vulnerabilities (reentrancy, flash loans, front-running)
Wants to implement DeFi patterns (AMM, lending, staking, vaults)
Needs gas optimization for contract deployment or execution
Asks about ERC standards (ERC-20, ERC-721, ERC-1155, ERC-4626)
Wants to set up Foundry or Hardhat testing for contracts
Needs an audit checklist or security review of a contract
Asks about upgradeable contracts, proxy patterns, or storage layout

Do NOT trigger this skill for:

Frontend dApp development with ethers.js/wagmi (use frontend-developer instead)
General cryptography concepts unrelated to smart contracts (use cryptography instead)

当用户有以下需求时触发此技能：

编写或评审Solidity智能合约
询问智能合约安全漏洞（重入、闪电贷、抢先交易）
想要实现DeFi模式（AMM、借贷、质押、金库）
需要针对合约部署或执行进行Gas优化
询问ERC标准（ERC-20、ERC-721、ERC-1155、ERC-4626）
想要为合约搭建Foundry或Hardhat测试环境
需要审计清单或合约安全评审
询问可升级合约、代理模式或存储布局

请勿在以下场景触发此技能：

使用ethers.js/wagmi进行前端dApp开发（请使用前端开发技能）
与智能合约无关的通用密码学概念（请使用密码学技能）

Key principles

核心原则

Security over cleverness - Every line of Solidity is an attack surface. Prefer well-audited OpenZeppelin implementations over custom code. "Don't be clever" is the cardinal rule - clever code hides bugs that drain funds.
Checks-Effects-Interactions (CEI) - Always validate inputs first (checks), update state second (effects), and make external calls last (interactions). This is the primary defense against reentrancy.
Gas is money - Every opcode has a cost paid by users. Optimize storage reads/writes (SSTORE is 20,000 gas), pack structs, use calldata over memory for read-only params, and batch operations where possible.
Immutability demands perfection - Deployed contracts cannot be patched. Use comprehensive testing (100% branch coverage), formal verification where feasible, and always get an independent audit before mainnet deployment.
Composability is a feature and a risk - DeFi's power comes from composability, but every external call is an untrusted entry point. Assume all external contracts are malicious. Use reentrancy guards and validate return values.

安全优先，拒绝炫技 - 每一行Solidity代码都是攻击面。优先使用经过审计的OpenZeppelin实现，而非自定义代码。"不要炫技"是首要准则——花哨的代码会隐藏导致资金损失的漏洞。
检查-效果-交互（CEI） - 始终先验证输入（检查），再更新状态（效果），最后进行外部调用（交互）。这是防范重入攻击的主要手段。
Gas就是金钱 - 每一条操作码都需要用户付费。优化存储读写（SSTORE消耗20,000 Gas）、打包结构体、对只读参数使用calldata而非memory，并尽可能批量操作。
不可变性要求完美 - 部署后的合约无法修补。使用全面测试（100%分支覆盖率）、可行的形式化验证，并在主网部署前始终进行独立审计。
组合性是特性也是风险 - DeFi的力量来自组合性，但每一次外部调用都是不可信的入口点。假设所有外部合约都是恶意的。使用重入防护并验证返回值。

Core concepts

核心概念

The EVM execution model determines everything in Solidity. Storage slots cost 20,000 gas to write (SSTORE) and 2,100 gas to read (SLOAD). Memory is cheap but ephemeral. Calldata is cheapest for function inputs. Understanding this cost model is essential for writing efficient contracts. See

references/gas-optimization.md

Solidity's type system and storage layout directly affect security. Storage variables are laid out sequentially in 32-byte slots. Structs can be packed to share slots. Mappings and dynamic arrays use keccak256 hashing for slot computation. Proxy patterns depend on storage layout compatibility between implementations.

DeFi building blocks are composable primitives: AMMs (constant product formula), lending protocols (collateralization ratios, liquidation), yield vaults (ERC-4626), staking (reward distribution), and governance (voting, timelocks). Each has well-known attack vectors. See

references/defi-patterns.md

The security landscape includes reentrancy, flash loan attacks, oracle manipulation, front-running (MEV), integer overflow (pre-0.8.0), access control failures, and storage collisions in proxies. A single missed check can drain an entire protocol. See

references/security-audit.md

EVM执行模型决定了Solidity的一切。存储槽写入（SSTORE）消耗20,000 Gas，读取（SLOAD）消耗2,100 Gas。内存成本低但临时。Calldata是函数输入的最便宜选择。理解这个成本模型是编写高效合约的关键。详见

references/gas-optimization.md

。

Solidity的类型系统和存储布局直接影响安全性。存储变量按顺序排列在32字节的槽中。结构体可以打包以共享槽。映射和动态数组使用keccak256哈希计算槽位置。代理模式依赖于实现之间的存储布局兼容性。

DeFi构建模块是可组合的原语：AMM（恒定乘积公式）、借贷协议（抵押率、清算）、收益金库（ERC-4626）、质押（奖励分配）和治理（投票、时间锁）。每个模块都有已知的攻击向量。详见

references/defi-patterns.md

。

安全领域包括重入、闪电贷攻击、预言机操纵、抢先交易（MEV）、整数溢出（0.8.0版本之前）、访问控制失败以及代理中的存储冲突。一个遗漏的检查可能导致整个协议资金流失。详见

references/security-audit.md

。

Common tasks

常见任务

Write a secure ERC-20 token

编写安全的ERC-20代币

Always inherit from OpenZeppelin. Never implement token logic from scratch.

solidity

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract MyToken is ERC20, Ownable {
    constructor(uint256 initialSupply)
        ERC20("MyToken", "MTK")
        Ownable(msg.sender)
    {
        _mint(msg.sender, initialSupply * 10 ** decimals());
    }

    function mint(address to, uint256 amount) external onlyOwner {
        _mint(to, amount);
    }
}

始终继承自OpenZeppelin。切勿从头实现代币逻辑。

solidity

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract MyToken is ERC20, Ownable {
    constructor(uint256 initialSupply)
        ERC20("MyToken", "MTK")
        Ownable(msg.sender)
    {
        _mint(msg.sender, initialSupply * 10 ** decimals());
    }

    function mint(address to, uint256 amount) external onlyOwner {
        _mint(to, amount);
    }
}

Prevent reentrancy attacks

防范重入攻击

Apply CEI pattern and use OpenZeppelin's ReentrancyGuard:

solidity

import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";

contract Vault is ReentrancyGuard {
    mapping(address => uint256) public balances;

    function withdraw(uint256 amount) external nonReentrant {
        // CHECKS
        require(balances[msg.sender] >= amount, "Insufficient balance");

        // EFFECTS (update state BEFORE external call)
        balances[msg.sender] -= amount;

        // INTERACTIONS (external call last)
        (bool success, ) = msg.sender.call{value: amount}("");
        require(success, "Transfer failed");
    }
}

应用CEI模式并使用OpenZeppelin的ReentrancyGuard：

solidity

import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";

contract Vault is ReentrancyGuard {
    mapping(address => uint256) public balances;

    function withdraw(uint256 amount) external nonReentrant {
        // 检查
        require(balances[msg.sender] >= amount, "Insufficient balance");

        // 效果（在外部调用前更新状态）
        balances[msg.sender] -= amount;

        // 交互（最后进行外部调用）
        (bool success, ) = msg.sender.call{value: amount}("");
        require(success, "Transfer failed");
    }
}

Optimize gas usage

优化Gas使用

Key patterns for reducing gas costs:

solidity

contract GasOptimized {
    // Pack structs - these fit in one 32-byte slot (uint128 + uint64 + uint32 + bool)
    struct Order {
        uint128 amount;
        uint64 timestamp;
        uint32 userId;
        bool active;
    }

    // Use immutable for constructor-set values (avoids SLOAD)
    address public immutable factory;
    uint256 public immutable fee;

    // Cache storage reads in memory
    function processOrders(uint256[] calldata orderIds) external {
        uint256 length = orderIds.length; // cache array length
        for (uint256 i; i < length; ) {
            // process order
            unchecked { ++i; } // safe: i < length prevents overflow
        }
    }

    // Use custom errors instead of require strings (saves deployment gas)
    error InsufficientBalance(uint256 available, uint256 required);

    function withdraw(uint256 amount) external {
        uint256 bal = balances[msg.sender]; // cache SLOAD
        if (bal < amount) revert InsufficientBalance(bal, amount);
        balances[msg.sender] = bal - amount;
    }
}

See

references/gas-optimization.md

for the full optimization checklist.

降低Gas成本的关键模式：

solidity

contract GasOptimized {
    // 打包结构体 - 这些可以放入一个32字节槽中（uint128 + uint64 + uint32 + bool）
    struct Order {
        uint128 amount;
        uint64 timestamp;
        uint32 userId;
        bool active;
    }

    // 对构造函数设置的值使用immutable（避免SLOAD）
    address public immutable factory;
    uint256 public immutable fee;

    // 将存储读取缓存到内存
    function processOrders(uint256[] calldata orderIds) external {
        uint256 length = orderIds.length; // 缓存数组长度
        for (uint256 i; i < length; ) {
            // 处理订单
            unchecked { ++i; } // 安全：i < length 防止溢出
        }
    }

    // 使用自定义错误而非require字符串（节省部署Gas）
    error InsufficientBalance(uint256 available, uint256 required);

    function withdraw(uint256 amount) external {
        uint256 bal = balances[msg.sender]; // 缓存SLOAD结果
        if (bal < amount) revert InsufficientBalance(bal, amount);
        balances[msg.sender] = bal - amount;
    }
}

完整的优化清单详见

references/gas-optimization.md

。

Implement an ERC-4626 tokenized vault

实现ERC-4626代币化金库

solidity

import "@openzeppelin/contracts/token/ERC20/extensions/ERC4626.sol";

contract YieldVault is ERC4626 {
    constructor(IERC20 asset_)
        ERC4626(asset_)
        ERC20("Yield Vault Token", "yvTKN")
    {}

    function totalAssets() public view override returns (uint256) {
        return IERC20(asset()).balanceOf(address(this));
    }
}

solidity

import "@openzeppelin/contracts/token/ERC20/extensions/ERC4626.sol";

contract YieldVault is ERC4626 {
    constructor(IERC20 asset_)
        ERC4626(asset_)
        ERC20("Yield Vault Token", "yvTKN")
    {}

    function totalAssets() public view override returns (uint256) {
        return IERC20(asset()).balanceOf(address(this));
    }
}

Set up Foundry testing

搭建Foundry测试环境

solidity

// test/Vault.t.sol
pragma solidity ^0.8.20;

import "forge-std/Test.sol";
import "../src/Vault.sol";

contract VaultTest is Test {
    Vault vault;
    address alice = makeAddr("alice");

    function setUp() public {
        vault = new Vault();
        vm.deal(alice, 10 ether);
    }

    function test_deposit() public {
        vm.prank(alice);
        vault.deposit{value: 1 ether}();
        assertEq(vault.balances(alice), 1 ether);
    }

    function test_withdraw_reverts_on_insufficient_balance() public {
        vm.prank(alice);
        vm.expectRevert("Insufficient balance");
        vault.withdraw(1 ether);
    }

    // Fuzz testing - Foundry generates random inputs
    function testFuzz_deposit_withdraw(uint96 amount) public {
        vm.assume(amount > 0);
        vm.deal(alice, amount);
        vm.startPrank(alice);
        vault.deposit{value: amount}();
        vault.withdraw(amount);
        vm.stopPrank();
        assertEq(vault.balances(alice), 0);
    }
}

solidity

// test/Vault.t.sol
pragma solidity ^0.8.20;

import "forge-std/Test.sol";
import "../src/Vault.sol";

contract VaultTest is Test {
    Vault vault;
    address alice = makeAddr("alice");

    function setUp() public {
        vault = new Vault();
        vm.deal(alice, 10 ether);
    }

    function test_deposit() public {
        vm.prank(alice);
        vault.deposit{value: 1 ether}();
        assertEq(vault.balances(alice), 1 ether);
    }

    function test_withdraw_reverts_on_insufficient_balance() public {
        vm.prank(alice);
        vm.expectRevert("Insufficient balance");
        vault.withdraw(1 ether);
    }

    // 模糊测试 - Foundry生成随机输入
    function testFuzz_deposit_withdraw(uint96 amount) public {
        vm.assume(amount > 0);
        vm.deal(alice, amount);
        vm.startPrank(alice);
        vault.deposit{value: amount}();
        vault.withdraw(amount);
        vm.stopPrank();
        assertEq(vault.balances(alice), 0);
    }
}

Audit a contract for common vulnerabilities

审计合约的常见漏洞

Walk through the contract checking for these in priority order:

Reentrancy - Any external call before state update? Any missing ReentrancyGuard?
Access control - Are admin functions properly gated? Is the owner set correctly?
Integer overflow - Using Solidity < 0.8.0 without SafeMath?
Oracle manipulation - Using spot prices from DEX pools? Use TWAP or Chainlink.
Flash loan attacks - Can state be manipulated within a single transaction?
Front-running - Can transaction ordering affect outcomes? Use commit-reveal.
Unchecked return values - Are low-level call return values checked?
Storage collisions - In proxy patterns, does the implementation share storage layout?

See

references/security-audit.md

for the full audit checklist.

按优先级顺序检查合约：

重入 - 是否在状态更新前进行外部调用？是否缺少ReentrancyGuard？
访问控制 - 管理员函数是否正确限制访问？所有者是否设置正确？
整数溢出 - 使用Solidity < 0.8.0版本且未使用SafeMath？
预言机操纵 - 使用DEX池的现货价格？请使用TWAP或Chainlink。
闪电贷攻击 - 能否在单笔交易中操纵状态？
抢先交易 - 交易顺序是否会影响结果？使用提交-揭示模式。
未检查返回值 - 是否检查低级调用的返回值？
存储冲突 - 在代理模式中，实现合约是否共享存储布局？

完整的审计清单详见

references/security-audit.md

。

Anti-patterns / common mistakes

反模式/常见错误

Mistake	Why it's dangerous	What to do instead
Rolling your own token logic	Subtle edge cases in transfer/approve lead to exploits	Use OpenZeppelin's battle-tested implementations
Using `tx.origin` for auth	Phishing attacks can relay transactions through malicious contracts	Always use `msg.sender` for authentication
External call before state update	Enables reentrancy - the attacker re-enters before balance is deducted	Follow CEI pattern: checks, effects, then interactions
Spot price from a DEX pool	Flash loans can manipulate pool reserves in a single tx	Use time-weighted average prices (TWAP) or Chainlink oracles
Unbounded loops over arrays	Loops that grow with user count will eventually exceed block gas limit	Use pull-over-push patterns, pagination, or off-chain computation
Using `transfer()` or `send()`	Hardcoded 2300 gas stipend breaks when receiver has logic	Use `call{value: amount}("")` with reentrancy guard
Magic numbers in code	Makes auditing impossible and introduces misconfiguration risk	Use named constants: `uint256 constant MAX_FEE = 1000;`

错误做法	危险原因	正确做法
自行编写代币逻辑	transfer/approve中的细微边界情况会导致漏洞利用	使用OpenZeppelin经过实战检验的实现
使用 `tx.origin` 进行授权	钓鱼攻击可通过恶意合约中继交易	始终使用 `msg.sender` 进行身份验证
状态更新前进行外部调用	会触发重入攻击——攻击者在余额扣除前重新进入合约	遵循CEI模式：检查、效果、然后交互
使用DEX池的现货价格	闪电贷可在单笔交易中操纵池储备	使用时间加权平均价格（TWAP）或Chainlink预言机
对数组使用无界循环	随用户数量增长的循环最终会超出区块Gas限制	使用拉取而非推送模式、分页或链下计算
使用 `transfer()` 或 `send()`	硬编码的2300 Gas津贴在接收方有逻辑时会失效	使用 `call{value: amount}("")` 并配合重入防护
代码中使用魔法数字	使审计无法进行并引入配置错误风险	使用命名常量： `uint256 constant MAX_FEE = 1000;`

Gotchas

注意事项

CEI pattern is violated by modifier usage - A common mistake is putting a reentrancy guard or balance check in a modifier that runs before state updates, then making an external call in the modifier. Modifiers execute around the function body, which means the external call in the modifier runs before
```
effects
```
in the function body. Keep the CEI pattern entirely within the function, not split across modifiers.
address.transfer()
and
address.send()
are deprecated but still taught - Both have a hardcoded 2300 gas stipend that will fail if the recipient is a contract with non-trivial receive logic. The correct pattern is
```
(bool success, ) = addr.call{value: amount}("")
```
combined with a ReentrancyGuard. New code should never use
```
transfer()
```
or
```
send()
```
.
Proxy storage collisions silently corrupt state - In upgradeable proxy patterns (TransparentProxy, UUPS), if the implementation contract declares state variables that overlap with the proxy's admin slot (slot 0), state corruption occurs on every write. Use OpenZeppelin's unstructured storage pattern for admin variables and verify storage layout with
```
forge inspect
```
before upgrading.
Foundry fuzz testing hits the default seed repeatedly without corpus expansion -
```
forge test --fuzz-runs 256
```
uses pseudo-random inputs that may not cover edge cases near integer boundaries. Always define
```
vm.assume()
```
guards for valid ranges and increase
```
fuzz.runs
```
in
```
foundry.toml
```
for security-critical functions. Use invariant testing for stateful properties.
Block timestamp is miner-manipulable within ~15 seconds - Using
```
block.timestamp
```
for time-sensitive logic (token vesting cliffs, auction deadlines) allows miners to shift outcomes by up to ~15 seconds. This is rarely exploitable in practice but becomes significant in high-value time-lock contracts. Use
```
block.number
```
with expected block time for coarser timing.

修饰符的使用会违反CEI模式 - 常见错误是将重入防护或余额检查放在修饰符中，而修饰符在函数体执行前运行，这意味着修饰符中的外部调用会在函数体的"效果"步骤前执行。请将CEI模式完全放在函数内部，不要拆分到修饰符中。
address.transfer()
和
address.send()
已被弃用但仍被教学 - 两者都有硬编码的2300 Gas津贴，当接收方有复杂逻辑时会失效。正确的模式是结合ReentrancyGuard使用
```
(bool success, ) = addr.call{value: amount}("")
```
。新代码绝不应使用
```
transfer()
```
或
```
send()
```
。
代理存储冲突会静默破坏状态 - 在可升级代理模式（TransparentProxy、UUPS）中，如果实现合约声明的状态变量与代理的管理员槽（槽0）重叠，每次写入都会导致状态损坏。对管理员变量使用OpenZeppelin的非结构化存储模式，并在升级前使用
```
forge inspect
```
验证存储布局。
Foundry模糊测试会重复使用默认种子而不扩展语料库 -
```
forge test --fuzz-runs 256
```
使用伪随机输入，可能无法覆盖整数边界附近的边缘情况。始终为有效范围定义
```
vm.assume()
```
防护，并针对安全关键函数增加
```
foundry.toml
```
中的
```
fuzz.runs
```
值。对有状态属性使用不变量测试。
区块时间戳可被矿工操纵约±15秒 - 将
```
block.timestamp
```
用于时间敏感逻辑（代币解锁 cliff、拍卖截止时间）会允许矿工将结果偏移约15秒。在实践中这很少被利用，但在高价值时间锁合约中会变得重要。请使用
```
block.number
```
结合预期区块时间进行粗略计时。

References

参考资料

For detailed content on specific topics, read the relevant file from

references/

```
references/security-audit.md
```
- Full audit checklist, common vulnerability catalog with real exploit examples
```
references/gas-optimization.md
```
- Complete gas optimization guide with opcode costs and storage layout
```
references/defi-patterns.md
```
- DeFi building blocks: AMM, lending, vaults, staking, governance patterns

Only load a references file if the current task requires deep detail on that topic.

如需特定主题的详细内容，请阅读

references/

中的相关文件：

```
references/security-audit.md
```
- 完整审计清单、带真实漏洞利用案例的常见漏洞目录
```
references/gas-optimization.md
```
- 包含操作码成本和存储布局的完整Gas优化指南
```
references/defi-patterns.md
```
- DeFi构建模块：AMM、借贷、金库、质押、治理模式

仅当当前任务需要该主题的深度细节时才加载参考文件。

Companion check

配套技能检查

On first activation of this skill in a conversation: check which companion skills are installed by running
ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null
. Compare the results against the
recommended_skills
field in this file's frontmatter. For any that are missing, mention them once and offer to install:
npx skills add AbsolutelySkilled/AbsolutelySkilled --skill <name>
Skip entirely if
recommended_skills
is empty or all companions are already installed.

在对话中首次激活此技能时：通过运行
ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null
检查已安装的配套技能。将结果与此文件前置元数据中的
recommended_skills
字段进行比较。对于任何缺失的技能，提及一次并提供安装命令：
npx skills add AbsolutelySkilled/AbsolutelySkilled --skill <name>
如果
recommended_skills
为空或所有配套技能已安装，则跳过此步骤。