Validate Ethereum addresses with EIP-55 checksum verification. Detect invalid addresses and mixed-case checksums.
Letter case can carry error-detection information in an Ethereum address. This validator checks whether a pasted value has the 20-byte hexadecimal address shape and whether mixed-case letters agree with EIP-55. A checksum covers the address text, not an account name, balance, owner, or network. The common surprise is that uniform lowercase or uppercase can still be treated as address-shaped, while mixed case that looks deliberate is invalid if even one letter has the wrong case.
A concrete input and expected output from the current implementation.
Input
0x52908400098527886E0F7030069857D2E4169Ee7
Expected output
Invalid Ethereum address: EIP-55 checksum mismatch.
The value has 40 hexadecimal characters, but one e near the end was changed from the uppercase form in the published EIP-55 test vector. That creates a mixed-case value whose casing no longer agrees with the checksum.
An Ethereum address represents 20 bytes, written as 40 hexadecimal characters. The conventional 0x marker is separate from those characters. Length and the allowed 0-9, a-f, and A-F character set determine whether the value has address syntax. A checksum cannot make a too-short, too-long, or non-hexadecimal value valid.
EIP-55 starts from the lowercase hexadecimal address without 0x and takes its Keccak-256 hash. For each address letter, the hash nibble at the same position controls case: values 8 through f require uppercase, while 0 through 7 require lowercase. Decimal digits never change case. A mixed-case address passes only when every letter follows those decisions.
No. The validator can establish only address syntax and, when applicable, consistency with EIP-55 capitalization. It cannot confirm who controls the address, whether it is an externally owned account or contract, whether it exists on the selected network, or whether a copied destination was maliciously replaced with another correctly checksummed address.
No reliable repair can recover intent. Recomputing capitalization for the supplied 20-byte value can produce a checksummed rendering, but that does not show whether the hexadecimal digits themselves are correct. Compare the value with a trusted source. If only case was lost, obtain the canonical EIP-55 form from the verified underlying address.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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