Ethereum Address Checksum

Ethereum addresses are 20 bytes written as 40 hexadecimal characters, and they have no built-in error detection: change one character and you have a different, perfectly valid address. Sending funds to the wrong one cannot be undone. EIP-55 added a safety net without changing the address itself, by encoding a checksum in the capitalisation of its letters. This page converts addresses to that form and tells you whether a pasted address passes.

How the checksum is built

Take the address in lower case, without the 0x prefix. Compute the Keccak-256 hash of that text, treated as ASCII characters. Then go through the 40 characters of the address together with the first 40 hexadecimal digits of the hash. Wherever the address has a letter from a to f and the hash digit at the same position is 8 or more, write the letter in upper case; otherwise leave it in lower case. Digits are never changed. The result looks random, but anyone can recompute it from the address.

What the three results mean

If an address has both upper and lower case letters and they match the pattern above, it has a valid checksum. If all its letters are of one case, it carries no checksum, and the page reports “No checksum” and shows what the checksummed version would be. If the mixed case does not match, the status is “Wrong checksum”: at least one character differs from what was generated, which means a typing error or a corrupted copy. A warning appears at the bottom whenever any address fails.

Using the page

Paste one address per line, with or without the 0x prefix. The table gives your input, the status and the EIP-55 form, and a button copies the checksummed list. Lines that are not 40 hexadecimal characters get an explanation: how many characters were found or that a character is not hexadecimal. A hundred addresses can be normalised in one go, which suits cleaning up an exported list or comparing addresses from two sources.

What the check does not do

A checksum shows that an address was copied exactly as it was generated. It does not show who controls the address, whether it belongs to a person, a contract or nobody, or whether it is safe to send to. It cannot tell you whether a lower-case address came from a legitimate source. Some chains that use Ethereum-style addresses apply a variant (EIP-1191) that mixes in the chain ID, and addresses written in that way will show as wrong on this page.

A worked example

The Sample button loads the test addresses from EIP-55. The first four, such as 0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed, are already in checksum form, and each is reported as a valid checksum. The next two are the same first address written in all lower case and all upper case; both are reported as having no checksum, and the table shows the mixed-case form. The last line is the first address with its final letter changed from lower to upper case; it is reported as a wrong checksum and a warning explains why.

Limits

The page checks format and checksum only. It does not contact a node, look up balances, resolve names such as ENS domains or recognise contracts. Use the original source of the address, a block explorer, or a small test transaction to confirm that it is the one you intend. Addresses with spaces inside, or with other prefixes, are not repaired automatically.

Related tools

• Wei to ETH Converter converts amounts between wei, gwei and ether.
• Hash Generator computes standard digests such as SHA-256.
• Base58 Encoder covers the checksum scheme used by Bitcoin addresses.
• BIP-39 Wordlist Inspector explains mnemonic phrases and their checksum.