Checksum Address Converter

What is EIP-55 Checksum Address?

An Ethereum address is 40 hex characters — easy to mistype by one character and lose your funds forever (transactions are irreversible). EIP-55 (Ethereum Improvement Proposal 55) solves this elegantly: hash the lowercase address with Keccak-256, then capitalize each hex letter where the corresponding hash bit is set. The pattern of upper/lowercase letters becomes a self-validating checksum — wallets and exchanges can detect ~99.986% of typos before broadcasting. This tool converts any address (all-lower, all-upper, or already-checksummed) to canonical EIP-55 format and validates existing checksums. Compatible with every EVM chain: Ethereum, Binance Smart Chain, Polygon, Arbitrum, Optimism, Base, Avalanche C-Chain, Fantom, Linea, zkSync, Scroll, Mantle, and the 100+ other Layer 1/2/3 networks that use Ethereum's address format.

Why Use Checksum Addresses?

• Error Detection: Mixed-case format helps detect typos in addresses
• Compatibility: Works with all EVM-compatible blockchains
• Safety: Reduces risk of sending funds to wrong addresses
• Standard: Widely supported by wallets and exchanges
• Validation: Easy to verify address correctness

What is EIP-55?

EIP-55 is an Ethereum Improvement Proposal that defines a checksum format for Ethereum addresses. It capitalizes specific letters in the address based on a hash of the address, creating a built-in error detection mechanism without changing the actual address value.

Are checksum addresses required?

While not technically required (lowercase addresses still work), checksum addresses are strongly recommended for safety. Most modern wallets and exchanges display addresses in checksum format by default to help prevent errors.

Which blockchains support this?

All EVM-compatible blockchains use the same address format and support EIP-55 checksums. This includes Ethereum, BSC (Binance Smart Chain), Polygon, Arbitrum, Optimism, Avalanche C-Chain, Fantom, Base, and many others.

Can I use lowercase addresses?

Yes, lowercase addresses are functionally identical and will work for transactions. However, they lack the error detection benefit of checksum addresses. It's best practice to always use the checksum format when copying or sharing addresses.

How does the checksum work?

The checksum is created by hashing the lowercase address with Keccak-256. Then, based on the hash value, certain letters in the address are capitalized. This creates a pattern that can be verified to detect errors without adding extra characters.

What happens if I send to a wrong-case address?

Functionally, nothing — Ethereum smart contracts treat the address as case-insensitive at the protocol level. Your transaction will go through to whatever address the bytes represent. The danger is upstream: many wallets (MetaMask, Trust Wallet, hardware wallets) refuse to send to an address whose mixed-case checksum doesn't validate, throwing 'Invalid address' to protect you. If your wallet accepts it, the transaction is valid; if it rejects it, the address has a typo somewhere — never override the warning.

Why don't Bitcoin addresses use EIP-55?

Bitcoin uses entirely different address formats (Base58Check, Bech32) that have their own checksum mechanisms baked into the encoding — they're case-sensitive by design (lowercase vs uppercase Bech32 are different). EIP-55 is Ethereum-specific and works only because Ethereum addresses are raw hex where case carries no protocol meaning. Don't try to apply EIP-55 to BTC, LTC, BCH, or DOGE addresses — it will produce invalid addresses and lost funds.

Can checksums detect deliberate scam swaps?

No, and that's important to understand. EIP-55 catches accidental typos with ~99.986% reliability but provides zero protection against malware that maliciously swaps your clipboard contents (clipboard hijackers are real and growing). Both the original and the substitute address may be valid checksum addresses. Always: verify the first 6 and last 6 characters on the wallet screen before signing, use hardware wallet address verification screens, and consider sending a small test transaction (0.001 ETH equivalent) first when moving large sums to a new address.

Do my addresses leave the browser?

No. This tool runs 100% client-side: every address you paste — single or batch — is validated and checksummed locally in your browser using the ethers.js getAddress() function and Keccak-256. Nothing is uploaded, logged, or sent to any server, and the CSV/JSON exports are generated entirely in memory and downloaded directly from your device. This makes it safe for exchange operators, payroll/airdrop distributors, auditors, and treasury teams to pre-flight large recipient lists without leaking who they are paying.

What is EIP-1191 and how does it differ from EIP-55?

EIP-55 computes the mixed-case checksum from Keccak-256 of the lowercase address alone. EIP-1191 is an optional, backward-incompatible extension that mixes the chain ID into the hash (prefixing the address with the chainId), so the same 40-hex address produces a different capitalization pattern on RSK (chainId 30/31) and a few other chains. Most Ethereum-ecosystem chains (ETH mainnet, BSC, Polygon, Arbitrum, Optimism, Base) use plain EIP-55, which is what this tool and ethers.js implement. If you are working specifically with RSK, validate against its EIP-1191 variant — a plain EIP-55 checksum will look 'invalid' there even though the underlying bytes are correct.

How to Use

• Copy any Ethereum address (can be uppercase, lowercase, or mixed)
• Paste it into the input field
• Click 'Convert to Checksum' button
• Copy the properly formatted checksum address for safe use