Barcode Check-Digit Validator — EAN-13, EAN-8, UPC-A

Catch a mistyped barcode before it reaches a label, a product feed or a warehouse system. This Actor validates the GS1 check digit of a batch of barcodes, and — if you send a code that is one digit short — computes the check digit you are missing.

Pure algorithm. No third-party API, no signup, no API key, and no network call of any kind during the check.

What it does

Every EAN-13, EAN-8 and UPC-A barcode ends with a check digit derived from the digits before it by the standard GS1 weighting scheme (alternating 3 and 1, summed, then subtracted from the next multiple of ten). This Actor applies that scheme in both directions:

• Validate mode — you send a complete code, it recomputes the expected check digit and tells you whether the one you sent matches.
• Compute mode — you send a code one digit short, it returns the code completed with the correct check digit.

The mode is chosen automatically from the length of what you send, so a mixed batch of complete and partial codes works in a single run.

Use cases

• Product feeds and catalogues — check a supplier's GTIN column before importing it, instead of discovering the bad rows downstream.
• Label printing — verify a code before committing it to physical labels, where a mistake costs a reprint.
• Warehouse and ERP data cleanup — bulk-check barcodes exported from a spreadsheet or an ERP in one run.
• Building a code — you have the GS1 prefix and item reference and need the trailing check digit computed correctly.

Input

{ "codes": ["4006381333931", "036000291452", "7351353", "400638133393"] }

codes is the only field, and it is required. Send full codes, partial codes, or a mix of both.

Output (one row per code)

{
  "input": "4006381333931",
  "format": "EAN-13",
  "mode": "validate",
  "valid": true,
  "expected_check_digit": 1,
  "corrected_code": "4006381333931",
  "verdict": "valid"
}

Pricing

Pay-per-event: $0.003 per barcode checked, charged once a completed answer is produced — whether the verdict is valid or invalid. An input that produces no answer because our own logic failed is never charged.

Limitations — read this before you buy

This is GS1 check-digit arithmetic only, for EAN-13, EAN-8 and UPC-A.

• It does not look up the product. There is no GTIN database behind it: it cannot tell you the brand, the name or the price of an item.
• ITF-14 and GS1-128 are not supported.
• A valid check digit means the code is internally consistent, not that the code has ever been assigned to a real product.

FAQ

Does a "valid" result mean the barcode exists? No. It means the check digit is arithmetically correct for the digits in front of it. Verifying that a GTIN is registered to a real product requires a product database, which this Actor deliberately does not use.

What happens with a code of the wrong length? It is reported with verdict: "invalid_format" rather than failing the run, so one bad row never stops a batch.

Related Actors

Part of the same family of small, single-purpose checkers on this account — each does one thing, priced per item checked:

• IBAN Validator & Formatter — ISO 13616 length + mod-97 checksum, fully offline.
• Card Number Validator (Luhn) — Luhn checksum and card-network detection, output is masked.
• EU VAT Number Checker — official VIES lookup.
• Email Address Validator — syntax, domain and MX checks.
• Password Strength Checker — entropy scoring, never returns the password.
• Cron Expression Validator — plain-English description and next run times.