ISSN Validator

ISSN validation: serial publications under ISO 3297

The ISSN — International Standard Serial Number is the persistent identifier for serial publications: scientific journals, magazines, newsletters, monograph series and any continuing resource. It is defined by ISO 3297 and assigned by the ISSN International Centre in Paris through a network of national agencies. Validating an ISSN is a short mod-11 calculation, but the standard hides several details that catch developers off guard — different agencies, two related identifiers (ISSN-L and eISSN) and a check digit that may legitimately be the letter X.

An ISSN is a string of 8 characters displayed as two four-character groups separated by a hyphen, e.g. 0378-5955 (the ISSN of Hearing Research). The first seven characters are digits 0-9; the eighth is the check digit, either a digit 0-9 or the letter X representing the value 10. The hyphen is mandatory in the canonical display form and is dropped during arithmetic. Unlike ISBN, the ISSN has no embedded geographic or publisher meaning — the digits are sequentially allocated by national centres.

Mod-11 algorithm step by step

Multiply the first seven digits by weights 8, 7, 6, 5, 4, 3, 2. Sum the products, take modulo 11 and compute 11 - remainder. If the result equals 10 the check digit is X; if it equals 11 the check digit becomes 0; otherwise it is the digit itself.

// 0378-595?
digits = [0,3,7,8,5,9,5]
sum    = 0*8 + 3*7 + 7*6 + 8*5 + 5*4 + 9*3 + 5*2
       = 160
160 % 11 = 6
dv = 11 - 6 = 5
// ISSN: 0378-5955

Implementation tip: the check digit is the only place where the character set extends beyond digits, so a strict input regex such as ^[0-9]{4}-?[0-9]{3}[0-9X]$ already rejects most malformed strings before you even reach the arithmetic.

ISSN, eISSN and ISSN-L

The same journal published in print and online has two separate ISSNs: the print ISSN and the electronic ISSN (eISSN). To make machine reconciliation possible, ISO 3297 introduced the ISSN-L (linking ISSN), a single value chosen by the ISSN Centre to represent the continuing resource regardless of medium. Library catalogues, citation databases and research evaluation systems use the ISSN-L to merge records — failing to use it leads to duplicate journal entries in reports.

Who issues ISSNs

• Brazil: the IBICT (Instituto Brasileiro de Informação em Ciência e Tecnologia) is the national centre. The standard fee is around R$ 200 per request.
• Portugal: Biblioteca Nacional de Portugal.
• United States: Library of Congress ISSN Center.
• United Kingdom: British Library.
• International: the ISSN International Centre handles publications that fall outside any national centre.

Where ISSN validation is required

• Academic indexing: Scopus, Web of Science, DOAJ, Latindex and CAPES Periódicos use ISSN as the primary key for journal records.
• Qualis CAPES: the Brazilian journal-quality classification requires a valid ISSN for every entry; without one, the journal is non-classifiable.
• SciELO and OJS (Open Journal Systems) instances refuse to import metadata without an ISSN.
• MARC 21: the 022 field stores the ISSN; cataloguing software validates it on save.
• ROAD (Directory of Open Access Scholarly Resources) lists open-access journals by ISSN.
• Crossref aggregates DOIs under a parent ISSN.

ISSN vs ISBN vs DOI

These three identifiers are easy to confuse but cover different objects. ISBN identifies a single book or monograph edition — once issued it does not change. ISSN identifies the serial as a whole, regardless of issue or volume. DOI identifies an individual article, dataset or chapter inside a serial; many DOIs share the same parent ISSN. A journal article is therefore often catalogued with all three: ISBN (rarely, only if the issue is republished as a book), ISSN (the journal) and DOI (the specific article).

Common errors

• Hyphen omitted: 03785955 is the same value as 0378-5955, but the canonical display always uses the hyphen.
• Lowercase x: a non-normalised x typed in the check-digit position should be uppercased before comparison.
• Confusing ISSN with eISSN: when both exist, citing only one of them fragments the record. Use the ISSN-L when available.
• Leading zeros stripped: spreadsheets silently turn 0378-5955 into 378-5955. Always store the ISSN as text.

FAQ

Does an ISSN identify a single article? No. It identifies the journal as a whole. Article-level identification needs a DOI.

Do I need an ISSN to be in Qualis CAPES? Yes. CAPES requires a valid ISSN; journals without one are not classified.

Is it free in Brazil? No. The IBICT charges around R$ 200 per request. International applications outside the IBICT scope go through the ISSN International Centre with separate fees.

Can the check digit really be the letter X? Yes — and only the last position. X represents the numeric value 10 and exists because mod 11 has eleven possible outcomes.

Does this validator query portal.issn.org? No. The arithmetic check is entirely local. To confirm that an ISSN is actually registered, consult portal.issn.org or the IBICT catalogue.