Contract Bytecode Diff Checker Between Deployments

WHAT IT DOES

This tool connects to your EVM wallet and reads contract bytecode from multiple deployed contract addresses across EVM chains. It compares the bytecode to detect differences, verify consistency between deployments, and identify potential mismatches or upgrades. The tool displays key metrics including bytecode length, keccak256 hash, and deployment status for each contract, and provides a summary indicating whether all deployed contracts share identical bytecode.

HOW TO USE

Connect your Web3 wallet using the Connect button. In the Contract Addresses textarea, enter each contract address you want to compare—one per line. Click "Compare Bytecode" to fetch and compare the bytecode from all provided addresses. Results appear in the Results card with a summary of contracts checked, comparison status, and hash match indicator, followed by a detailed breakdown of each contract. Click "Show Hashes Only" to view a condensed view showing only the bytecode hashes for quick comparison.

TECHNICAL MECHANISM: ON-CHAIN BYTECODE RETRIEVAL AND HASH COMPARISON

The tool uses ethers.js to fetch bytecode from deployed contracts via provider.getCode(address). For each contract address, the tool retrieves the current bytecode from the chain and determines whether the contract is deployed (code is non-empty). The keccak256 hash of each bytecode is computed using ethers.utils.keccak256(). The tool then compares the hashes across all deployed contracts to determine if the bytecode is identical. The results display includes bytecode length, hash, and a preview of the first few bytes. The summary indicates whether all deployments share the same bytecode (✅ All bytecode identical), detect differences (❌ Differences detected), or if no contracts are deployed (⚠️ No contracts deployed). All comparisons are performed using cryptographic hashes for efficient and accurate verification.

WHAT IT CANNOT SEE

This tool cannot determine the semantic meaning of bytecode differences—identical bytecode hashes indicate bytecode-level equivalence, but the tool cannot interpret what the differences mean or whether they are security-relevant. It cannot distinguish between intentional upgrades and malicious modifications—the tool only detects differences, not their intent or legitimacy. It cannot verify that source code corresponds to bytecode without external verification—the tool only compares bytecode as it exists on-chain. It relies on on-chain bytecode queries and may be rate-limited by RPC providers—multiple queries may be throttled. It cannot detect differences in contract state or storage layout—the tool only checks the code, not the contract's state.

PLEASE NOTE

This is a read-only tool—it never signs transactions or requests write permissions. All data is fetched on-demand and stored only in memory; nothing is persisted across page reloads. The tool supports EVM chains only—Ethereum, Polygon, BSC, Arbitrum, Optimism, Avalanche, Base, and Fantom. Always verify that the contract addresses you enter are correct. Bytecode differences may be expected for proxy contracts or upgradeable patterns—always consider the contract design when interpreting comparison results.