ISSN Validator
Validate ISSN check digits.
Overview
The ISSN Validator checks whether an International Standard Serial Number — the 8-digit code used to identify magazines, journals, newspapers and other periodicals — has a valid check digit. Paste a string with or without the customary hyphen and the validator strips formatting, runs the algorithm and reports whether the code is valid plus the canonical "XXXX-XXXX" form.
The tool is used by librarians cataloguing periodicals, citation managers building bibliographies and publishers verifying a freshly assigned code from a national ISSN agency. Long-tail queries it covers include "validate ISSN online", "ISSN check digit modulo 11" and "what is an ISSN number".
How it works
An ISSN is exactly 8 characters: 7 digits followed by a check digit that may be 0-9 or X. The check digit uses a modulo-11 weighted sum, weighting positions 1 through 7 by 8, 7, 6, 5, 4, 3 and 2 respectively. The check digit is the value that, when added to the weighted sum, makes the total a multiple of 11. As with ISBN-10, X stands for the value 10.
The validator strips the hyphen and any whitespace, normalises X to uppercase, then computes the expected check digit and compares it to the supplied digit. If they match the ISSN is structurally valid; otherwise the tool reports the expected check digit so you can spot the typo.
Examples
0317-8471 → Valid ISSN
0028-0836 → Valid (Nature)
1476-4687 → Valid (Nature, electronic version)
1234-5678 → Invalid (expected check digit: 9)
FAQ
Why does an ISSN have a hyphen in the middle?
The hyphen is a readability convention rather than part of the data — exactly like the hyphens in an ISBN. It always falls between the fourth and fifth digit.
Why does an ISSN sometimes end in X?
The modulo-11 algorithm produces check values from 0 to 10. The value 10 is written as X because there is no single digit for it.
Can a print and electronic edition share an ISSN?
No. Each format gets its own ISSN. The print edition of a journal and its online edition are tracked as separate serial publications.
Is an ISSN guaranteed to be globally unique?
Yes, once assigned by an ISSN national centre. The international ISSN centre in Paris coordinates allocations so codes do not collide.
What's the relationship between ISSN and DOI?
ISSN identifies the serial publication as a whole. DOI identifies a specific article, issue or other published unit. They are complementary identifiers, often used together in citations.