npi-checksum

Tiny, dependency-free TypeScript validator for U.S. national provider identifier (NPI) checksums.

• Node.js 22+
• Ships both ESM and CommonJS builds
• Zero runtime dependencies
• Tree-shakeable named exports

This validator only verifies the NPI checksum. It does not prove that an identifier was issued, is active, or belongs to a particular person or organization. We designed this package for fast UI feedback, not identity verification.

Install

npm install npi-checksum

Usage

import { passesNpiChecksum } from "npi-checksum";

passesNpiChecksum("1234567893"); // true

API

passesNpiChecksum(value: string | null | undefined): boolean

Checks that the value:

1. contains exactly 10 digits,
2. starts with 1 or 2 (the range CMS reserves for NPIs), and
3. satisfies the NPI Luhn check-digit calculation with the 80840 healthcare-provider prefix.

The NPI checksum is defined by the U.S. Centers for Medicare & Medicaid Services (CMS): Requirements for National Provider Identifier (NPI) and NPI Check Digit.

passesNpiChecksum("1234567893"); // true
passesNpiChecksum("1234567890"); // false

Build

dist/ is compiled from src/index.ts by the TypeScript compiler. That is a development dependency only: installing the package pulls down nothing but dist/, and there are no runtime dependencies.

npm run build

npm test and npm pack run the build automatically, so dist/ is never stale or missing.

Tests

Tests use Node's built-in node:test runner, so no test framework is required. The published package contains standard ESM JavaScript plus TypeScript declarations, compiled from src/index.ts in this repository.

npm test

Authors

Lemma provides banking solutions for healthcare companies. Many of our customers build healthcare apps that work with NPIs, so we open sourced this package to help them ship faster.

0BSD License

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted.

THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.