EIP-55 Ethereum Address Checksum Tool

Ethereum addresses are 40 hexadecimal characters. On their own they carry no error detection — a single mistyped character produces a different valid-looking address and the funds are lost. EIP-55 solves this by encoding a Keccak-256 checksum into the capitalisation: certain letters are uppercased and others stay lowercase, following rules derived from the hash of the lowercase address. This tool applies that checksum and validates whether any address you paste already has the correct one.

Load Sample inserts a known checksummed address: 0x742d35Cc6634C0532925a3b8D4C9fA8b2D3f7A1e. Pressing it again cycles through four more examples, including the Ethereum Foundation address and the USDC contract, so you can see both valid and un-checksummed forms side by side. Pasting an all-lowercase or all-uppercase address returns a warning and shows the corrected mixed-case form immediately.

How It Calculates the Checksum

1. Take the 40 hex characters of the address in lowercase (without the 0x prefix).
2. Compute Keccak-256 of those 40 ASCII bytes using the Ethereum variant of the hash — not NIST SHA-3, which uses different padding and would produce the wrong result.
3. For each of the 40 characters: if the corresponding nibble in the 32-byte hash is 8 or greater, uppercase that character. Otherwise leave it lowercase.
4. Prepend 0x to the resulting mixed-case string. That is the EIP-55 checksummed address.

Validation Results and What Each Means

• Valid EIP-55 checksum: the capitalisation exactly matches the hash-derived pattern. Safe to use in contract calls, wallet imports, and UIs.
• Invalid checksum: the input has mixed case but the capitalisation does not match the Keccak-256 rule. This is the scenario EIP-55 was designed to catch — it indicates a likely transcription error. The corrected address is shown in the result card below the banner.
• All lowercase / all uppercase: these are technically valid hex addresses but carry no checksum. Most modern tooling accepts them, but an all-lowercase address gives wallets and block explorers no way to flag a typo.
• Not a valid address: the input is not exactly 40 hex characters. Common causes are a missing character, an accidental space, or the wrong number of digits.

Accuracy Limits

• A correctly checksummed address has roughly a 1-in-2³² (about one-in-four-billion) chance of passing validation after a random single-character mutation. EIP-55 is a checksum, not a signature — it detects accidental errors but not intentional forgery.
• This tool validates and converts the address format only. It cannot verify whether an address has ever received funds, whether it is a contract, or whether it belongs to anyone in particular.
• ENS names (like vitalik.eth) and ICAP addresses are not Ethereum hex addresses and will return the "not a valid address" result. Resolve them to a hex address first.