NPI validation
US National Provider Identifier (CMS) — checksum: Luhn mod-10 with CMS prefix 80840. Free in your browser, or over the JSON API.
What it is
US National Provider Identifier (CMS). 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
Luhn mod-10 with CMS prefix 80840. 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 |
|---|---|---|---|
| 1234567893 | valid | 3 | 3 |
API
curl "https://<your-worker>.workers.dev/v1/validate/npi/1234567893"
This type has a single trailing check digit, so CodeCheck can also compute it:
GET /v1/complete/npi/{body}
Try it in the browser demo — the demo runs the same code offline.