What is an EIP-55 checksum?

EIP-55 encodes a checksum into the capitalisation of an Ethereum address. Each hex letter is uppercased or lowercased based on the keccak256 hash of the lowercase address. A wallet can then detect a mistyped address because random typos rarely produce valid casing.

Why does my all-lowercase address still pass as valid hex?

An all-lowercase or all-uppercase address has no checksum information to verify, so it is accepted as a valid format but is flagged as un-checksummed. Only mixed-case addresses carry the EIP-55 checksum that this tool can confirm or reject.

How is the checksum computed?

Take the keccak256 hash of the lowercase 40-character hex address as an ASCII string. For each hex character, look at the corresponding nibble of the hash: if it is 8 or greater and the character is a letter, uppercase it; otherwise leave it lowercase.

Does this run entirely in my browser?

Yes. The keccak256 hashing and all comparison happen locally in JavaScript. No address is ever sent over the network, which matters because addresses can be linked to your holdings and activity.

Will a wallet reject a bad checksum?

Most modern wallets and dApps refuse to send to a mixed-case address whose checksum fails, treating it as a likely typo. All-lowercase addresses are usually accepted without a warning, which is why pasting the checksummed form is safer.

EIP-55 Checksum Address Validator

EIP-55 hides an error-detecting checksum inside the capitalisation of an Ethereum address. This validator runs keccak256 in your browser to confirm whether a mixed-case address is correctly checksummed and to produce the canonical checksummed form of any address.

How it works

The checksum capitalises each hex letter based on the address’s own hash:

lower   = address without 0x, lowercased
hash    = keccak256( ascii bytes of lower )   (256-bit)
for each hex char at position i:
  nibble = i-th hex digit of hash
  if char is a letter (a-f) and nibble ≥ 8 → uppercase it
  else → leave lowercase

If the input is mixed-case, it is valid only when its casing exactly matches this computed form. All-lowercase or all-uppercase inputs carry no checksum and are reported as un-checksummed but format-valid.

Example and tips

The address 0xfb6916095ca1df60bb79ce92ce3ea74c37c5d359 checksums to 0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359. Paste either and the tool returns the checksummed version; paste a mixed-case variant with one letter’s case wrong and it fails. Always copy the checksummed output before sending funds — it is the single cheapest safeguard against a fat-fingered address, catching the overwhelming majority of single-character typos.