Checkdigit compute

checkdigit-compute · version 1.0.0 · Identifiers & check digits · free, no key needed

Compute the check digit(s) for a payload under a named algorithm (Luhn, Verhoeff, Damm, ISO 7064, GS1, mod 10).

Use when you need to: compute a luhn check digit · calculate iso 7064 check digits · verhoeff check digit calculator.

Decide before calling

Read the versioned contract and the supported scope below. Reuse checkdigit-compute@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 checkdigit-compute@1.0.0 for compute a luhn check digit. 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

• compute a luhn check digit
• calculate iso 7064 check digits
• verhoeff check digit calculator
• gs1 check digit for a barcode payload
• damm algorithm check digit
• mod 97 check digits for an identifier payload
• swiss mod 10 recursive check digit
• חישוב ספרת ביקורת

Not supported

• validating a full value that already has a check digit attached (use checkdigit-validate)
• identifier-specific structure such as IBAN country rules, ISIN prefixes, or GS1 key lengths
• lowercase payload letters or separators such as spaces or hyphens

Behavior

• payload must match ^[0-9A-Z]+$ (uppercase ASCII digits and letters only, 1-64 characters); lowercase letters, separators, or any other character throw invalid_input before any algorithm-specific check runs.
• Per-algorithm payload alphabet: luhn, verhoeff, damm, gs1-mod10, mod10-recursive, iso7064-mod11-2 and iso7064-mod11-10 accept decimal digits 0-9 only. iso7064-mod661-26 accepts letters A-Z only. iso7064-mod37-2, iso7064-mod37-36, iso7064-mod97-10 and iso7064-mod1271-36 accept digits 0-9 and letters A-Z. A payload character outside the named algorithm's alphabet throws invalid_input.
• full = payload concatenated with check_digits, in that order; no separators and no rearrangement.
• Pure arithmetic on the payload string; no locale, clock, or randomness; identical output across runs for the same input.

Input

• payload (string, required): min length 1; max length 64; pattern ^[0-9A-Z]+$
• algorithm (one of "luhn", "verhoeff", "damm", "iso7064-mod11-2", "iso7064-mod11-10", "iso7064-mod37-2", "iso7064-mod37-36", "iso7064-mod97-10", "iso7064-mod661-26", "iso7064-mod1271-36", "gs1-mod10", "mod10-recursive", required)

Output

• check_digits (string, required): min length 1; max length 2; pattern ^[0-9A-Z*]{1,2}$
• full (string, required): min length 2; max length 66; pattern ^[0-9A-Z*]+$
• algorithm (one of "luhn", "verhoeff", "damm", "iso7064-mod11-2", "iso7064-mod11-10", "iso7064-mod37-2", "iso7064-mod37-36", "iso7064-mod97-10", "iso7064-mod661-26", "iso7064-mod1271-36", "gs1-mod10", "mod10-recursive", required)

Limits

• max payload bytes: 64

Example

Request input:

{
  "payload": "411111111111111",
  "algorithm": "luhn"
}

Response:

{
  "result": {
    "check_digits": "1",
    "full": "4111111111111111",
    "algorithm": "luhn"
  }
}

How to call it

MCP

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

{
  "id": "checkdigit-compute",
  "version": "1.0.0",
  "input": {
    "payload": "411111111111111",
    "algorithm": "luhn"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/checkdigit-compute/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"payload":"411111111111111","algorithm":"luhn"}'

The machine-readable contract is at /v1/tools/checkdigit-compute/versions/1.0.0.

CLI

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

Get the client at /clients/cli/.

Related tools

• Checkdigit validate: Validate a full value's trailing check digit(s) against a named algorithm (Luhn, Verhoeff, Damm, ISO 7064, GS1, mod 10).
• Gs1 key validate: Validate a GTIN-8/12/13/14, GLN, SSCC or GSIN's GS1 mod-10 check digit and look up its 3-digit GS1 prefix meaning.
• Upu s10 validate: Validate a 13-char UPU S10 postal identifier's weighted mod-11 check digit, split service indicator and country.
• Iccid validate: Validate a 19/20-digit ICCID's Luhn check digit, require the 89 major industry id, split issuer/account digits.
• 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.