Validate a US ABA routing number with its checksum online, in your browser.
Check a 9-digit US bank routing (ABA) number against its official checksum. A passing result means the number is well-formed; it does not confirm the specific bank.
A 9-digit code identifying a US financial institution for ACH and wire transfers — the number on the bottom-left of a check.
That the nine digits are internally consistent (weights 3-7-1). It catches typos but not whether the bank exists.