Free LEI, ISIN, CUSIP and SEDOL check digit validator
Check an identifier’s check digit.
Validate the check digits of LEIs, ISINs, CUSIPs, SEDOLs and Luhn numbers. Paste a value and the type is detected from its shape; the arithmetic is shown step by step.
- Runs in your browser
- Type detected for you
- Same check over REST and MCP
Never paste a live card number
Identifier
Spaces and hyphens are ignored; letters are read as upper case.
Result
Valid ISIN
Detected from its shape. Check digit 5 match.
- Country
- US
- NSIN
- 037833100
- Check digit
- 5
- Type
- ISIN (International Securities Identification Number, ISO 6166) — detected
- Check digit
- 5 — matches
- Country code
- US
- Country
- United States of America
- National number (NSIN)
- 037833100
- Embedded CUSIP
- 037833100
- Embedded CUSIP check digit
- Valid
- Check digit only: whether an ISIN is allocated is recorded by the national numbering agency (ANNA).
Use it from codeSame answer over REST or MCP · no key
curl -s 'https://payopskit.com/api/v1/identifier/US0378331005'For agents: the same check is the MCP tool validate_identifier on https://payopskit.com/mcp — no key, no sign-up.
How the check digit works
Every one of these identifiers ends in a check digit computed from the characters before it, so most single-character typos and most swaps of neighbouring characters are caught. Not all: SEDOL, ISIN and Luhn check digits miss some swaps (Luhn misses 09↔90), so a valid check digit doesn’t prove the value was copied correctly.
An ISIN (ISO 6166) is a country code, a nine-character national number and one check digit. Replace each letter with two digits (A = 10 … Z = 35): US037833100 becomes 3028037833100. Then apply Luhn: from the right, double every other digit, add the digits of each result.
| Character | 3 | 0 | 2 | 8 | 0 | 3 | 7 | 8 | 3 | 3 | 1 | 0 | 0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Value | 3 | 0 | 2 | 8 | 0 | 3 | 7 | 8 | 3 | 3 | 1 | 0 | 0 |
| Double? | ×2 | ×1 | ×2 | ×1 | ×2 | ×1 | ×2 | ×1 | ×2 | ×1 | ×2 | ×1 | ×2 |
| Adds | 6 | 0 | 4 | 8 | 0 | 3 | 5 | 8 | 6 | 3 | 2 | 0 | 0 |
Sum 45; check digit = (10 − 45 mod 10) mod 10 = 5. It matches the last digit.
Which identifier is which
Auto picks the type from the value’s shape; choose one explicitly when a value fits more than one.
| Identifier | Length | What it is |
|---|---|---|
| LEI | 20 characters | Legal Entity Identifier (ISO 17442): who a counterparty is. Two check digits, ISO 7064 mod 97-10. |
| ISIN | 12 characters | International Securities Identification Number (ISO 6166): country code, national number, Luhn check digit. |
| CUSIP | 9 characters | US and Canadian securities: issuer, issue and a modulus-10 "double-add-double" check digit. |
| SEDOL | 7 characters | London Stock Exchange securities: six digits or consonants and a weighted check digit. |
| Luhn | 12–19 digits | Payment card numbers (and others) use the Luhn mod 10 check digit. |
What a valid check digit proves — and what it doesn’t
- A matching check digit means the value is well formed. It does not mean the identifier was issued or is still current.
- Whether an LEI is issued and current is recorded by GLEIF; ISINs by the national numbering agencies (ANNA).
- A card number that passes Luhn can still be closed, expired or never issued; the network shown is a hint from the leading digits.
- Nothing you type here leaves this page: the check runs in your browser.
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