Developer Tools
Barcode Validator
Validate UPC-A, EAN-13, EAN-8, GTIN-14, ISBN-10, ISBN-13, and ISSN check digits in your browser. Calculate missing digits and convert ISBN-10 to ISBN-13.
Paste a complete code. Format is detected automatically. Check digit is recomputed and compared.
Spaces, dashes, and underscores are ignored. The trailing character X is uppercased automatically. The format is inferred from the length and prefix.
Sample codes
Result
Valid barcode
Format
ISBN-13
Formatted
978-0-306406-15-7
Compact
9780306406157
Body
978030640615
Check digit
7
Length
13 of 13 expected
How the check digits work
- GTIN family (UPC-A, EAN-13, EAN-8, GTIN-14, ISBN-13): walk the data digits from right to left, multiply alternating positions by 3 and 1 starting with 3, sum the products, then the check digit is the number that brings the total up to the next multiple of 10.
- ISBN-10: multiply the nine data digits by 10, 9, 8, ..., 2 from left to right, sum them, take the result mod 11, subtract from 11, take mod 11 again. A value of 10 is written as the letter X.
- ISSN: multiply the seven data digits by 8, 7, 6, ..., 2, sum them, then mod-11 and (11 minus) the same way ISBN-10 does. The check character may also be X.
A passing check digit confirms the code is well-formed and likely typed or scanned correctly. It does not confirm that the product, book, or journal actually exists, only that the digits match the published algorithm.
Format reference
| Format | Length | Check rule | Notes |
|---|---|---|---|
| UPC-A | 12 | GTIN mod-10 | 12-digit retail barcode used in North America. Identical math to GTIN-12. |
| EAN-13 | 13 | GTIN mod-10 | 13-digit retail barcode used worldwide outside North America. Identical math to GTIN-13. |
| EAN-8 | 8 | GTIN mod-10 | 8-digit barcode used for small products where EAN-13 will not fit. |
| GTIN-14 | 14 | GTIN mod-10 | 14-digit packaging identifier (ITF-14 / SSCC carton codes). Same check-digit rule as EAN-13. |
| ISBN-10 | 10 | Mod-11 (X allowed) | Legacy 10-character book identifier. Last character is mod-11 and may be the letter X (representing 10). |
| ISBN-13 | 13 | GTIN mod-10 | Current 13-digit book identifier with prefix 978 or 979. Same check-digit math as EAN-13. |
| ISSN | 8 | Mod-11 (X allowed) | 8-character serial identifier for journals and magazines, printed as XXXX-XXXX. Mod-11 check, last may be X. |
How to use
- Paste a barcode into the input. Format is detected from length and prefix, so UPC, EAN, GTIN, ISBN, and ISSN all work without a mode switch.
- Read the pass or fail verdict. When the check digit is wrong, the expected value is shown so you can correct it.
- Switch to Calculate check digit to fill in the trailing digit for a code body you typed yourself.
- Switch to Convert ISBN to rewrite an ISBN-10 as an ISBN-13 (or the other way, for 978-prefixed values).
- Switch to Batch list to paste one code per line. Copy the results as CSV for the warehouse or library spreadsheet.
About this tool
Barcode Validator checks and computes the check digit for the retail-barcode family used in stores, warehouses, libraries, and supply chains: UPC-A (GTIN-12), EAN-13 (GTIN-13), EAN-8 (GTIN-8), GTIN-14 (used on ITF-14 cartons and SSCC packaging labels), ISBN-10, ISBN-13, and ISSN. The validator detects the format from the length and prefix of what you paste, strips spaces and hyphens, normalizes a trailing lowercase x to uppercase X (for ISBN-10 and ISSN), recomputes the check digit with the published algorithm, and reports a clean pass or fail. When the check is wrong, the expected check digit is shown so you can spot the off-by-one that caused it, which is the single most common cause of a failed scan or a mistyped catalogue number. A calculate-check-digit mode is included for the inverse use case: paste a partial code (the body without the trailing check digit) and the tool returns the digit that completes a valid code, ready to print on a label or hand to a barcode generator. The ISBN converter rewrites a valid ISBN-10 as the equivalent ISBN-13 by adding the 978 Bookland prefix and recomputing the check digit, and turns a 978-prefixed ISBN-13 back into the original ISBN-10. (979-prefixed ISBN-13 values are 13-digit only and have no 10-digit form, and the tool says so explicitly.) A batch mode lets you paste a column of mixed codes from a spreadsheet or scanner export, validates them line by line, and gives you a one-click CSV of the results for quick reconciliation. Every algorithm here is the published modular-arithmetic rule from the GS1 General Specifications (mod-10 weighted 3-1-3-1 from the right for GTINs) and the ISO standards for ISBN-10 (mod-11 weighted 10..2) and ISSN (mod-11 weighted 8..2). The full ISBN-10 and ISSN algorithm allows the check character X, which represents the value 10 and is otherwise impossible to write in one digit. Useful when a paste from a vendor PDF flips one digit, when a hand-typed UPC fails to scan at a kiosk, when migrating a library catalogue from ISBN-10 to ISBN-13, when an EDI export contains malformed GTINs, when a warehouse import rejects an ITF-14 carton code, when auditing an old book inventory against the modern ISBN registry, or when a barcode font has rendered ambiguous digits. All math runs locally in your browser; the codes you paste here are never uploaded.
Free to use. Works in your browser. No signup, no login.
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