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What is a checksum?
A checksum is a small extra value calculated from a piece of data and stored with it, so that a typo or corruption can be detected. Crypto addresses and seed phrases carry checksums, which is why a wallet can often reject a mistyped address before anything is sent.
What it means for you
A checksum catches accidental mistakes, not deliberate ones: a scammer's address, or a look-alike address planted in your history, has a perfectly valid checksum. An all-lowercase Ethereum address skips the capitalisation check entirely. Compare the full address with the intended recipient, not just whether the wallet accepted it.
A common mistake: “If my wallet accepted the address, it must be the right one.”
In fact: Acceptance only means the checksum matched, so the address is well-formed. A scammer's address or a poisoned look-alike passes the same check; the checksum cannot know who you meant to pay.
How it works
A checksum is a value computed from data and kept with it to detect changes, and each format builds its own. Bech32 Bitcoin addresses end in six checksum characters that detect any error affecting up to four characters, with under a 1 in 10^9 chance of missing larger errors. BIP-39 appends the first ENT/32 bits of the entropy's SHA-256 hash, four bits for a 12-word phrase. EIP-55 sets the case of each letter in an Ethereum address from its Keccak-256 hash, so a mistyped address passes with about 0.0247% probability.
Sources: BIP-173: Base32 address format (bech32), BIP-39: Mnemonic code for generating deterministic keys, EIP-55: Mixed-case checksum address encoding · checked 4 October 2026
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