Free Solidity Smart Contract Security Scanner

Why Every Solidity Developer Needs a Security Scanner

Smart contract vulnerabilities have caused billions of dollars in losses across DeFi. The DAO hack, the Parity wallet freeze, the Wormhole bridge exploit, countless flash loan attacks — each one exploited a bug that automated scanning could have flagged before deployment.

The problem is that most security audit firms charge $5,000 to $50,000+ per audit, with wait times measured in weeks. That puts professional security review out of reach for most developers, especially during active development when you need feedback the most.

The Solari Smart Contract Scanner solves this by providing free, instant vulnerability analysis directly in your browser. Paste your Solidity code, click scan, and get actionable results in seconds — no account creation, no API keys, no cost.

How the Free Solidity Scanner Works

The scanner uses pattern-based static analysis to identify known vulnerability classes in your Solidity source code. It parses your contract, maps control flow, and matches against a database of 20+ battle-tested vulnerability signatures.

What Vulnerabilities Does It Detect?

The scanner covers the most exploited vulnerability classes in production smart contracts. Here are the 10 categories it checks, with specifics on what gets flagged.

Vulnerability Examples the Scanner Catches

Let's walk through concrete code patterns that the scanner flags, so you can understand exactly what it looks for and why each pattern is dangerous.

Example 1: Reentrancy (Critical)

The classic reentrancy bug — sending ETH via a low-level call before updating the sender's balance. An attacker contract can re-enter the withdraw function before balances[msg.sender] is decremented, draining the contract.

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

    // BUG: External call before state update
    (bool success,) = msg.sender.call{value: amount}("");
    require(success);

    balances[msg.sender] -= amount; // Too late!
}

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

    balances[msg.sender] -= amount; // State update FIRST

    (bool success,) = msg.sender.call{value: amount}("");
    require(success);
}

Example 2: Unprotected Initialize (Critical)

Upgradeable contracts use initialize() instead of constructors. If this function lacks access control, anyone can call it and claim ownership of the contract.

// Anyone can call this and become the owner
function initialize(address _owner) external {
    owner = _owner;
}

import "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";

function initialize(address _owner) external initializer {
    owner = _owner;
}

Example 3: tx.origin Authentication (High)

Using tx.origin for authentication is dangerous because it returns the original sender of the transaction, not the immediate caller. An attacker can trick the owner into calling a malicious contract that then calls the vulnerable function.

function emergencyWithdraw() external {
    require(tx.origin == owner, "Not owner"); // Phishable!
    payable(owner).transfer(address(this).balance);
}

function emergencyWithdraw() external {
    require(msg.sender == owner, "Not owner"); // Direct caller only
    payable(owner).transfer(address(this).balance);
}

Example 4: Unbounded Loop DoS (Medium)

Iterating over a dynamic array with no upper bound means an attacker can grow the array until the function exceeds the block gas limit, permanently bricking the contract.

function batchTransfer(address[] calldata recipients, uint256[] calldata amounts) external {
    for (uint256 i = 0; i < recipients.length; i++) { // No upper bound!
        payable(recipients[i]).transfer(amounts[i]);
    }
}

uint256 constant MAX_BATCH = 50;

function batchTransfer(address[] calldata recipients, uint256[] calldata amounts) external {
    require(recipients.length <= MAX_BATCH, "Too many");
    for (uint256 i = 0; i < recipients.length; i++) {
        payable(recipients[i]).transfer(amounts[i]);
    }
}

Who Should Use This Scanner?

• Solidity developers — catch vulnerabilities during development, before they reach testnet or mainnet
• DeFi protocol teams — quick sanity check before committing to a full manual audit
• Smart contract auditors — automated first pass to identify common patterns, freeing time for business logic review
• Security researchers — rapid triage of contracts during bug bounty hunting
• Hackathon builders — ship safer code under time pressure without waiting for an audit
• Students and learners — understand common vulnerability patterns with concrete examples

Scan Tiers: Free, Standard, and Comprehensive

The basic pattern scan is free with no limits. For deeper analysis that catches business logic flaws and economic exploits, upgrade to a paid tier.

Free Solidity Scanner vs. Paid Audit Firms

Professional audit firms serve an important role for pre-mainnet security review. But they are expensive, slow, and inaccessible during development. Here is where the free scanner fits in your security workflow:

• During development: Run the free scanner on every commit. Catch reentrancy, access control, and other pattern-based bugs immediately — before they get to code review.
• Before testnet deployment: Run the $99 Standard scan for AI-powered deep analysis that catches business logic flaws pattern matching cannot detect.
• Before mainnet launch: Use the $199 Comprehensive audit for a full report covering DeFi-specific attack surfaces, flash loan vectors, and oracle manipulation analysis.
• For critical deployments: Combine automated scanning with a manual audit from a reputable firm. Our scanner catches the known patterns; human auditors find novel attack vectors.

Frequently Asked Questions