Help: CS1 errors

==<span id="bad_isbn">Check |isbn= value</span>==
<section begin="bad_isbn_help_text" />{{help desk}}{{#invoke:Cs1 documentation support|help_text_error_messages|err_bad_isbn|$1=&lt;type>}}

{{cs1}} and {{cs2}} templates that contain {{para|isbn}} are checked to ensure that the [[ISBN]] is the proper length (ten or thirteen digits), that the ISBN uses the correct optional separators (simple space or hyphen), and that the final [[check digit]] is correct according to the ISBN specification. Only one ISBN is allowed in this field because the whole {{para|isbn}} value is included in the citation's [[COinS]] [[metadata]]. See also [[Wikipedia:COinS]]. More than one ISBN, or characters that are not part of the ISBN, corrupt the COinS metadata and may also corrupt the link to [[Special:BookSources]]. (If relevant, they can be specified using {{para|id|{{tlp|ISBN|...}}}} instead.)

The error message &lt;type> indicator can be:
: {{error-small|length}} – ISBN is not 10 or 13 digits
: {{error-small|checksum}} – ISBN has one or more incorrect digits; look for typos and transposition
: {{error-small|invalid character}} – ISBN has one or more 'digits' that is not in the allowed set appropriate to ISBN length
: {{error-small|invalid prefix}} – 13-digit ISBNs must begin with '978' or '979'
: {{error-small|invalid form}} – 10-digit ISBNs with the mis-positioned 'X' character
: {{error-small|invalid group id}} – 13-digit ISBN begins with '9790'; this prefix / group ID combination is reserved to [[ISMN]]
To resolve this error, ensure that the {{para|isbn}} value is correct, that only one ISBN is used, that the proper optional separators are used, and that no other text is included. Use the ISBN printed on the work rather than one retrieved from third-party sources. If ''both are available'', use the 13-digit ISBN. When a 10-digit ISBN is used, if the check digit is a lowercase 'x', change it to an uppercase 'X'.

* '''Do not''' try to resolve the error by simply recalculating the check digit.  The check digit is there to check whether the main part of the number is correct.  If the ISBN is failing to validate, it is likely that there is a typo in the main part of the number.  In this case, recalculating the check digit results in an apparently valid ISBN that leads to the wrong source (or to nowhere).
* If you only have a 10-digit ISBN, '''do''' use the number as-is, do not try to convert it to the 13-digit form.
* If the ISBN as printed in your source is refusing to validate, '''do''' check both the front matter and the book cover for ISBNs.  It is not uncommon for the ISBN to be misprinted in the front matter but correct on the cover.
* '''Do''' preview your edit and check that the new ISBN does now link to the correct source.

In very rare cases, publishers have released books with malformed ISBNs. If you are certain that a non-conforming ISBN truly corresponds to the published work, then you can add [[Help:Citation_Style_1#Accept-this-as-written_markup|accept-this-as-written markup]] around the identifier to suppress the error message. In many cases, books may have been reissued with a corrected ISBN. Use a corrected ISBN when possible.

Sometimes there are numbers assigned to {{para|isbn}} that appear to be legitimate – length is right, check digit is correct – but that aren't true ISBN numbers.  This [http://isbn.org/ISBN_converter tool] may be helpful.

See also [[Wikipedia:ISBN]].

Pages with this error are automatically placed in {{#invoke:cs1 documentation support|help_text_cats|err_bad_isbn|pages=yes}}.<ref group="lower-alpha" name="categories" /><!-- See [[bugzilla:47049]] about {{FULLPAGENAME}}, category pagenames containing ISBN, and #ifeq: --><section end="bad_isbn_help_text" />