EIP-55 Address Checksum Tool
Check Ethereum addresses against the EIP-55 mixed-case checksum, repair lowercase ones, and see exactly which characters are wrong when validation fails.
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An Ethereum address has no built-in checksum, so EIP-55 added one for free
Unlike a Bitcoin address, a raw Ethereum address is twenty bytes of hexadecimal with no error detection at all. A single mistyped character produces another perfectly valid-looking address, and funds sent there are gone. EIP-55 solves this without changing the address format or breaking anything, by using the case of the hexadecimal letters to carry the checksum: a letter is capitalised where the corresponding bit of the keccak hash of the lowercase address is set. An all-lowercase address is still accepted everywhere, which is what made the scheme adoptable, and it is also why the protection is optional in practice.
The protection is about four bits per letter position
Roughly fifteen of the forty characters in a typical address are letters carrying a case bit, giving in the region of 2^15 combinations that a random error would have to hit exactly. That is enough to catch essentially every accidental transposition or single-character slip, and not enough to be a cryptographic guarantee. It defends against typing errors, which is what it was designed for, and not against an attacker who computes an address whose checksum matches.
Mixed case that fails is a stronger signal than all-lowercase
An all-lowercase address carries no checksum information, so it is neither valid nor invalid, only unchecked. An address with mixed case that fails validation is different: something changed it after it was correctly generated, which usually means a transcription error, a truncated copy or, occasionally, clipboard-substitution malware. A wallet that silently accepts a failing mixed-case address is discarding the one signal the format provides.
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Frequently Asked Questions
What does the mixed case in an address mean?
It is the EIP-55 checksum. A hexadecimal letter is capitalised where the corresponding bit of the keccak hash of the lowercase address is set, so the case pattern encodes an error-detecting code without changing the address format.
Is an all-lowercase address wrong?
No, it is unchecked. Lowercase addresses remain valid everywhere, which is what made the scheme adoptable, and it is also why the protection is optional in practice.
How much protection does it give?
About fifteen case-carrying letters in a typical address, so roughly one in thirty thousand random errors would pass. That catches essentially every accidental typo and is not a cryptographic guarantee.
What if a mixed-case address fails validation?
Treat it as suspect. Something altered it after correct generation, which usually means a transcription error or a truncated copy, and occasionally clipboard-substitution malware.
Does this apply to other chains?
Any EVM chain using the same address format uses the same checksum. EIP-1191 adds the chain ID into the hash on some chains, which makes an address checksummed for one chain fail on another, and that variant is not applied here.
Privacy & Security
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How to Use
Paste Ethereum addresses to validate or repair their checksums.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.