Isin validate

isin-validate · version 1.0.0 · Identifiers & check digits · free, no key needed

Validate a 12-character ISIN's ISO 6166 Luhn check digit and parse its country prefix, NSIN and NSIN scheme.

Use when you need to: validate an isin · check isin check digit · is this isin number valid.

Decide before calling

Read the versioned contract and the supported scope below. Reuse isin-validate@1.0.0 when your input, required output and limits match it. Choose another approach for an unsupported operation.

Explain the choice

"I can use isin-validate@1.0.0 for validate an isin. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

Supported

• validate an isin
• check isin check digit
• is this isin number valid
• isin checksum validator
• verify international securities identification number
• parse isin country code and nsin
• check digit for a stock isin
• does this isin belong to cusip or sedol

Not supported

• looking up which company or security an ISIN actually identifies
• computing an ISIN from a country and national number (see isin-compute-from-nsin)
• validating the CUSIP or SEDOL check digit embedded in the NSIN (see cusip-validate / sedol-validate)

Behavior

• isin must be exactly 12 characters: no case folding, no separators, no trimming. Any other length is reason wrong_length, checked first.
• Positions 1-2 (country_prefix), 3-11 (nsin) and 12 (check_digit) are the raw positional substrings whenever isin is exactly 12 characters, regardless of whether the per-position charset or the check digit itself is valid.
• Positions 1-2 must be A-Z; positions 3-11 must be A-Z or 0-9; position 12 must be 0-9, else reason invalid_character.
• country_prefix must be an officially assigned ISO 3166-1 alpha-2 code (data_version) or one of the ISIN-specific prefixes XS, EU, XA, XB, XC, XD, else reason unknown_country_prefix.
• Check digit: expand country_prefix+nsin (11 characters) to decimal digits (a digit stays itself; A=10 ... Z=35), concatenate, then Luhn: double every digit at an odd 1-based position from the right (the rightmost expanded digit is doubled, subtracting 9 from any doubled value over 9); the expected check digit is (10 - sum mod 10) mod 10. A mismatch is reason check_digit_mismatch.
• nsin_type is "cusip" for raw country_prefix US or CA, "sedol" for GB, IE, IM, JE or GG, and "other" otherwise; it depends only on the raw prefix, never on charset or check-digit validity, and is null only when length already failed.
• valid is true only when length, charset, country recognition and the check digit all pass, in that order; only one reason is ever returned.

Input

• isin (string, required): min length 1; max length 12

Output

• valid (boolean, required)
• reason (one of null, "wrong_length", "invalid_character", "unknown_country_prefix", "check_digit_mismatch", required)
• country_prefix (string or null, required): min length 2; max length 2
• nsin (string or null, required): min length 9; max length 9
• check_digit (string or null, required): min length 1; max length 1
• nsin_type (one of null, "cusip", "sedol", "other", required)
• data_version (string, required)

Limits

• max isin bytes: 12

Example

Request input:

{
  "isin": "US0378331005"
}

Response:

{
  "result": {
    "valid": true,
    "reason": null,
    "country_prefix": "US",
    "nsin": "037833100",
    "check_digit": "5",
    "nsin_type": "cusip",
    "data_version": "iso3166-1-2026-09-28"
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "isin-validate",
  "version": "1.0.0",
  "input": {
    "isin": "US0378331005"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/isin-validate/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"isin":"US0378331005"}'

The machine-readable contract is at /v1/tools/isin-validate/versions/1.0.0.

CLI

node cli.mjs run isin-validate 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• Upu s10 validate: Validate a 13-char UPU S10 postal identifier's weighted mod-11 check digit, split service indicator and country.
• Cusip validate: Validate a 9-character CUSIP's Modulus 10 Double Add Double check digit and parse its issuer, issue and PPN marker.
• Iban validate: Validate an IBAN's country, registry length, BBAN structure and MOD 97-10 check digits, and parse its bank/branch code.
• Imo number validate: Validate a 7-digit IMO ship identification number's weighted mod-10 check digit, with or without the 'IMO ' prefix.
• Iso6346 container validate: Validate an 11-character ISO 6346 container number's mod-11 check digit and split the owner code, category and serial.
• Sedol validate: Validate a 7-character SEDOL's weighted modulus 10 check digit and report whether it is a legacy all-numeric code.