ABA validation
US ABA routing transit number — checksum: ABA mod-10 (weights 3,7,1). Free in your browser, or over the JSON API.
What it is
US ABA routing transit number. CodeCheck verifies three things separately — format, length and check digit — and returns the expected and provided check digit, so a failed value tells you exactly what is wrong instead of just saying no.
Algorithm
ABA mod-10 (weights 3,7,1). The answer is derived from the value itself, with no database lookup and no third-party call, so it is deterministic, fast and privacy-safe.
Examples
| Value | Result | Expected | Provided |
|---|---|---|---|
| 021000021 | valid | — | 1 |
API
curl "https://<your-worker>.workers.dev/v1/validate/aba/021000021"
This type has a single trailing check digit, so CodeCheck can also compute it:
GET /v1/complete/aba/{body}
Try it in the browser demo — the demo runs the same code offline.