Issn validate

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

Validate an 8-digit ISSN's mod 11 check digit (X allowed) and compute its 977-prefixed EAN-13 barcode form.

Use when you need to: validate an issn · check issn check digit · convert issn to ean 13 barcode.

Decide before calling

Read the versioned contract and the supported scope below. Reuse issn-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 issn-validate@1.0.0 for validate an issn. 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 issn
• check issn check digit
• convert issn to ean 13 barcode
• is this issn valid
• issn checksum validator
• journal serial number check digit
• turn an issn into a 977 barcode

Not supported

• looking up which journal or serial an ISSN actually identifies
• validating an ISBN or ISMN (see isbn-validate / ismn-validate)
• computing the L-ISSN (linking ISSN) across print and electronic versions

Behavior

• issue_variant is optional and defaults to '00'; when provided it must be exactly 2 digits, else invalid_input.
• issn accepts two lengths: 9 characters 'NNNN-NNNNc' with a literal '-' at position 5 (positions 1-4 and 6-8 are the 7 core digits, position 9 is the check character), or 8 characters with no separator (positions 1-7 core digits, position 8 the check character). Any other length is reason wrong_length, checked first.
• issn (the normalized NNNN-NNNN form) and check_digit are always reconstructed from those raw positions, regardless of whether any character is actually a valid digit; both are null only when length already failed.
• invalid_character fires when, for the 9-character form, position 5 is not '-', or any core digit position is not 0-9, or the check character is neither a digit nor 'X'.
• ean13 requires only that the 7 core digits are all 0-9: ean13 = '977' + core digits + issue_variant + a freshly computed EAN-13 check digit (weight 1,3 alternating, mod 10) over the resulting 12 digits; ean13 is null when a core digit is invalid, even if the overall reason is invalid_character only because of the check character or hyphen.
• Check digit (only evaluated once the hyphen/core/check-character positions are all valid): weights 8,7,6,5,4,3,2 over the 7 core digits; expected check character is (11 - sum mod 11) mod 11, X when 10. A mismatch is reason check_digit_mismatch.
• valid is true only when length, charset and the check digit all pass, in that order; only one reason is ever returned.

Input

• issn (string, required): min length 1; max length 9
• issue_variant (string, optional): min length 2; max length 2; pattern ^[0-9]{2}$

Output

• valid (boolean, required)
• reason (one of null, "wrong_length", "invalid_character", "check_digit_mismatch", required)
• issn (string or null, required): min length 9; max length 9
• check_digit (string or null, required): min length 1; max length 1
• ean13 (string or null, required): min length 13; max length 13

Limits

• max issn bytes: 9

Example

Request input:

{
  "issn": "0378-5955"
}

Response:

{
  "result": {
    "valid": true,
    "reason": null,
    "issn": "0378-5955",
    "check_digit": "5",
    "ean13": "9770378595002"
  }
}

How to call it

MCP

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

{
  "id": "issn-validate",
  "version": "1.0.0",
  "input": {
    "issn": "0378-5955"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/issn-validate/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"issn":"0378-5955"}'

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

CLI

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

Get the client at /clients/cli/.

Related tools

• Isbn validate: Validate an ISBN-10 (mod 11, X allowed) or ISBN-13 (EAN mod 10) check digit and return the other form when it exists.
• Ismn validate: Validate an ISMN's EAN mod 10 check digit in M-form or 979-0 form and return the canonical 13-digit form.
• Checkdigit validate: Validate a full value's trailing check digit(s) against a named algorithm (Luhn, Verhoeff, Damm, ISO 7064, GS1, mod 10).
• Iccid validate: Validate a 19/20-digit ICCID's Luhn check digit, require the 89 major industry id, split issuer/account digits.
• Isin validate: Validate a 12-character ISIN's ISO 6166 Luhn check digit and parse its country prefix, NSIN and NSIN scheme.
• Iso6346 container validate: Validate an 11-character ISO 6346 container number's mod-11 check digit and split the owner code, category and serial.