Bytecode Similarity Comparator (Clone Detection)

WHAT IT DOES

Bytecode Similarity Comparator (Clone Detection) is a read-only security tool that compares the bytecode of two EVM smart contracts to detect clones, forks, and related deployments. It computes a normalized similarity score by comparing bytecode hex strings, accounting for differences in length and common prefixes. The tool provides a clear visual similarity percentage, categorizes results (Identical, Very Similar, Moderately Similar, Somewhat Similar, or Different), and highlights potential clone relationships. It helps developers, auditors, and security researchers identify duplicate contracts, detect deployed contract patterns, verify deployment authenticity, and track contract lineage across networks.

HOW TO USE

Connect your EVM-compatible wallet via the BGWallet bridge and select the network where both contracts are deployed. Enter the two contract addresses to compare and click "Compare Similarity". The tool fetches bytecode from both addresses, normalizes the hex strings, computes a Jaccard-like similarity score based on character-by-character matches and prefix alignment, and displays a detailed results page. The page includes the similarity percentage, a visual progress bar, bytecode sizes for both contracts, a status label, and a verdict indicating whether the contracts are likely clones. All analysis is read-only—no signatures or transactions are submitted.

TECHNICAL MECHANISM

The tool uses ethers.js v5.7.2 to fetch contract bytecode from both addresses via provider.getCode(address). Each bytecode string is normalized by stripping the "0x" prefix. The similarity algorithm compares the two hex strings character by character up to the minimum length, counts matching characters, and divides by the maximum length of the two strings. This produces a normalized score between 0 and 1. The score is then boosted by 0.05 if the first 20 characters (10 bytes) match, which accounts for common compiler metadata prefixes that often remain identical even when contracts differ. The tool also computes bytecode sizes in bytes (hex length divided by 2) to provide size context. Results are categorized based on similarity thresholds: 100% = Identical, >85% = Very Similar (likely clone), >60% = Moderately Similar, >30% = Somewhat Similar, ≤30% = Different. The analysis is purely static and deterministic, providing consistent results across runs without requiring source code or execution.

WHAT IT CANNOT SEE

This tool has fundamental limitations that users must understand. It cannot definitively prove two contracts are clones without source code matching—high bytecode similarity indicates likely clones but does not guarantee identical functionality without source verification. It cannot distinguish between clones with identical bytecode but different storage states—two contracts with identical bytecode may have different runtime storage values that affect their behavior. It cannot detect clones created via CREATE2 with different initialization parameters—contracts deployed with the same bytecode but different constructor arguments will appear identical despite being different instances. It cannot identify clones that have been upgraded or modified after deployment—if a contract has been changed after deployment, the bytecode comparison may miss the relationship. It cannot analyze clones that use proxy patterns where the implementation address differs—proxy contracts have minimal bytecode and the actual logic resides elsewhere. It cannot detect clones that have been minified, obfuscated, or compiled with different compiler versions, as these produce different bytecode even for the same source. It cannot determine the original source code or verify the authenticity of the deployed contract. The tool's similarity score is a heuristic and should not be used as sole evidence for clone detection without additional verification.

PLEASE NOTE

This tool only supports EVM-compatible blockchains (Ethereum, Polygon, BSC, Avalanche C-Chain, Optimism, Arbitrum, and their testnets). Solana, Tron, Starknet, SUI, TON, Aptos, Bitcoin, Cosmos, and XRP are not supported. The tool is free, open-source, requires no API keys, and uses the wallet's native provider for all read operations. Similarity scores are estimates and should be validated with source code review when available.