CAS Number Validator

Use this CAS number validator to check whether a CAS Registry Number is structurally valid before it lands in your catalog, safety data sheet index, or compliance feed. Paste one number or upload a column of thousands — every check runs in your browser, so your supplier data never leaves your machine.

What it checks

A CAS Registry Number looks simple, but a single transposed digit can break a chemical lookup or hide a regulated substance. This tool inspects each value and reports:

• Format — confirms the number follows the 2–7 digits – 2 digits – 1 digit pattern (for example 7732-18-5 for water), with hyphens in the right positions.
• Length bounds — flags numbers that are too short or too long to be a legitimate CAS assignment.
• Check digit — recomputes the final digit using the official CAS algorithm and compares it to the digit supplied.
• Common data errors — detects leading/trailing whitespace, stray characters, missing hyphens, and Excel-style number coercion that drops leading zeros or reformats values into scientific notation.
• Batch summary — when you paste or upload a list, it returns a pass/fail count and isolates the exact rows that need attention, so a buyer enriching an MRO or industrial range can fix the handful of bad records instead of re-keying the whole file.

How it works

Every CAS Registry Number ends in a single check digit derived from the digits before it. Reading the number right to left (ignoring the hyphens), each digit is multiplied by an incrementing weight starting at 1, the products are summed, and the check digit equals that sum modulo 10.

1. 1
   Strip and split
   The number is cleaned of whitespace and split on its hyphens into the main block, the two-digit middle block, and the single check digit.
2. 2
   Weight each digit
   Digits are read right to left and multiplied by 1, 2, 3, and so on.
3. 3
   Sum and take modulo 10
   The weighted products are summed and divided by 10; the remainder is the expected check digit.
4. 4
   Compare
   If the expected digit matches the supplied one and the format is intact, the value passes.

The check digit catches the most common real-world failures: a single mistyped digit and most digit transpositions introduced when someone copies a value off a label, a PDF safety data sheet, or a supplier spreadsheet.

All of this happens client-side. The tool is plain JavaScript running in your browser — there is no upload, no account, and no file-size limit. You can validate a one-off number or a full chemical master file without your data touching a server, which matters when you are handling proprietary supplier ranges. Once values are validated, the same approach scales: Claro applies check-digit and format rules across millions of records as part of automated product data enrichment, with provenance attached to every field it writes back.

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