Help:CS1 errors

This page describes the error messages reported by the Citation Style 1 and Citation Style 2 citations, what they mean, and how editors might resolve the errors. Category:CS1 errors is the general errors category and Category:CS1 maintenance is the general maintenance category.

Errors in the <ref> system can be found at Help:Cite errors.

Controlling error message display

By default, Citation Style 1 and Citation Style 2 error messages are visible to all readers and maintenance category messages are hidden from all readers.

To display maintenance messages, include the following text in your common CSS page or your specific skin's CSS page (common.css and skin.css respectively):

To display hidden-by-default error messages:

Even with this CSS installed, older pages in Wikipedia's cache may not have been updated to show these error messages even though the page is listed in one of the tracking categories. A null edit will resolve that issue.

To hide normally-displayed error messages:

You can personalize the display of these messages (such as changing the color), but you will need to ask someone who knows CSS or at the technical village pump if you do not understand how.

Most common errors

|access-date= requires |url=

|access-date= requires |url=

The |access-date= (or its alias, |accessdate=) is the date that the online resource addressed by |url= was added to the article. If |access-date= has been included in the citation without |url= then this message appears. If the citation does not use a web link, then |access-date= is redundant and should be removed.

When the online resource has a publication or other fixed date associated with it, |access-date= is of limited value though may be useful in identifying an appropriate archived version of the resource. Without |url=, |access-date= is not considered useful.

To resolve this error, provide a value for |url= or remove |access-date=. Editors should try to determine why the citation has |access-date= without |url=. For example, the citation may never have had a |url=, or |url= may have been removed because it links to a site that violates the creator's copyright (see WP:COPYLINK), or because |url= was deemed to be dead. If the citation never had |url= or it was removed for copyright violations, remove |access-date=. When a dead |url= has been removed, restore the |url= and if possible repair it (see WP:LINKROT).

Pages with this error are automatically placed in Category:Pages using citations with accessdate and no URL (2,336 pages).[a]

|archive-url= is malformed

|archive-url= is malformed: <reason>

Archive.org allows a variety of URLs to access snapshots of an archived page. Some of these are:

https://web.archive.org/web/YYYYMMDDhhmmss/http://www.example.com – a single snapshot; this is the preferred form for use with |archive-url=
https://web.archive.org/web/*/http://www.example.com – a wildcard search results page; useful for locating an appropriate snapshot but not appropriate in a citation
https://web.archive.org/web/201603/http://www.example.com – incomplete timestamp; archive.org returns the most recent snapshot
https://web.archive.org/save/http://www.example.com – saves a new snapshot of the current target; do not use this form

There are two forms of the basic URL:

https://web.archive.org/<timestamp>/... – the old form
https://web.archive.org/web/<timestamp><flags>/... – the new form

The error message identifies the reason for the message. The reasons are:

save command – the archive.org URL is the save command
pathweb/ was expected but something else was found
timestamp – the timestamp portion of the URL path is not 14 digits
flag – the flag portion of the URL path (if present; new form URLs only) is not 2 lowercase letters followed by an underscore: 'id_'
livewebliveweb.archive.org is a deprecated form of the domain name

When the archive.org URL has any of these errors, Module:Citation/CS1 does not link to archive.org and emits an appropriate error message.

To resolve this error, choose the URL of an appropriate snapshot from those held at archive.org. Search for the target URL.

Pages with this error are automatically placed in Category:Pages with archiveurl citation errors.[a]

|archive-url= requires |archive-date=

|archive-url= requires |archive-date=

|archive-date= (or its alias, |archivedate=), identifies the date that the web resource was archived.

To resolve this error, provide a value for |archive-date=. For web resources archived at archive.org,[1] the archival date can be found in the |archive-url=; for resources archived at webcitation.org,[2] the cache date is included in the archive header.

Pages with this error are automatically placed in Category:Pages with archiveurl citation errors.[a]

|archive-url= requires |url=

|archive-url= requires |url=

A properly formatted citation that includes |archive-url= and |archive-date= requires |url=. When the citation includes |url-status=live, the ordering of elements in the rendered citation is changed to put the original URL first.

To resolve this error, provide a value for |url=. For web resources archived at archive.org,[1] the original URL can be found in the |archive-url= value; for resources archived at webcitation.org,[2] the original URL is included in the archive header.

Pages with this error are automatically placed in Category:Pages with archiveurl citation errors.[a]

|arxiv= required

|arxiv= required

{{cite arXiv}} requires one, but not both, of the identifier parameters |arxiv= or |eprint= to specify an arXiv identifier.

To resolve this error, ensure that the template has |arxiv= or |eprint= with a properly constructed value.

Pages with this error are automatically placed in Category:CS1 errors: arXiv.[a]

|chapter= ignored

|chapter= ignored

Citation Style 1 templates {{cite web}}, {{cite news}}, {{cite journal}}, {{cite press release}}, {{cite podcast}}, {{cite newsgroup}}, as well as template {{citation}} when it uses |work= or any of its aliases, do not support |chapter= or the aliases |contribution=, |entry=, |article=, or |section=.

To resolve this error:

  • use a more appropriate citation template, or
  • place the content of the |chapter= parameter in |title=, or
  • for {{cite news}}, |department= can be used to give the name of the newspaper's section, such as "Obituaries", or
  • for {{citation}}, remove |work= or its aliases such as |website= and place their content in |title= if appropriate

Pages with this error are automatically placed in Category:CS1 errors: chapter ignored.[a]

Check |arxiv= value

Check |arxiv= value

When Citation Style 1 and Citation Style 2 templates contain |arxiv=, a test is done to see if the arXiv identifier conforms with the arXiv identifier scheme.[3] The identifier is checked for a valid number of digits in the article id; valid year and month values; and properly-placed hyphens, slashes, and dots.

To resolve this error, ensure that the |arxiv= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: arXiv.[a]

Check |asin= value

Check |asin= value

When Citation Style 1 and Citation Style 2 templates contain |asin=, a test is done to see if the ASIN identifier contains ten upper-case alphanumeric characters without punctuation or spaces and that if the first character is numeric, that the ASIN conforms to the rules for a ten-digit ISBN.

To resolve this error, ensure that the |asin= value is correct.

If the |asin= value is correct and all-numeric, use |isbn= instead and delete any |asin-tld= parameters. Articles with CS1 citations that use |asin= with all numeric values are categorized in Category:CS1 maint: ASIN uses ISBN.

Pages with this error are automatically placed in Category:CS1 errors: ASIN.[a]

Check |bibcode=

Check |bibcode= <message>

When Citation Style 1 and Citation Style 2 templates contain |bibcode=, a test is done to see if the bibcode identifier has the proper format.[4] Bibcodes are expected to match these requirements:

length must be 19 characters (<message> = ' length')
characters in position(s): (except as specified otherwise, violations produce ' value' in the <message> portion of the error message):
1–4 must be digits and must represent a year in the range of 1000 – next year (<message> = ' year')
5 must be a letter
6–8 must be a letter, ampersand, or dot (ampersand cannot directly precede a dot; &. (<message> = ' journal'))
9 must be a letter or dot
10–18 must be a letter, digit, or dot
19 must be a letter or dot

To resolve this error, ensure that the |bibcode= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: bibcode.[a]

Check |biorxiv= value

Check |biorxiv= value

When Citation Style 1 and Citation Style 2 templates contain |biorxiv=, a test is done to see if the bioRxiv identifier has the proper form. There are two valid forms:

six numeric characters without punctuation or spaces.
ymd format date prefix followed by six numeric characters without punctuation or spaces followed by optional version:
|biorxiv=yyyy.mm.dd.######v# where:
yyyy.mm.dd. – represents a date no earlier than 11 December 2019 ( 2019.12.11.) and no later than tomorrow's date; date must be a valid date
###### – 6-digit bioRxiv identifier
v# – optional version indicator

A common error is to include the bioRxiv URL (https://dx.doi.org/10.1101/<BIORXIV>), or the biorxiv DOI (10.1101/<BIORXIV>)

To resolve this error, ensure that the |biorxiv= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: bioRxiv.[a]

Check |citeseerx= value

Check |citeseerx= value

When Citation Style 1 and Citation Style 2 templates contain |citeseerx=, a test is done to see if the CiteSeerX identifier has the proper format. The expected identifier is the value assigned to the ?doi= query key in the URL of a CiteSeerX document. (This query key should not be confused with a Digital Object Identifier: it should not be input as |doi=.)

For instance, if you want to link to http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.220.7880, use |citeseerx=10.1.1.220.7880.

Pages with this error are automatically placed in Category:CS1 errors: citeseerx.[a]

Check date values in: |=, |=, ...

Check date values in: |<param1>=, |<param2>=, ...

When Citation Style 1 and Citation Style 2 templates contain date-holding parameters, an automated test is done to see if the dates are real dates that comply with a subset of the date rules in Wikipedia's Manual of Style, specifically checking for violations of MOS:DATEFORMAT.

To resolve this error, ensure that the date is an actual date and that the date format follows the Wikipedia Manual of Style's guidance on dates in the named parameter. See examples of unacceptable dates and how to fix them, below. Or, some conceptual issues to look for:

  • impossible dates, such as 29 February 2011 (2011 was not a leap year)
  • |access-date= must specify a day, not just a month or year.
  • misplaced, incorrect, or extraneous punctuation
  • extraneous text
  • hyphens or slashes instead of en dashes in date ranges (en dashes are required)
  • misspelling or improper capitalization (see MOS:ALLCAPS for more detail that is not in Wikipedia Manual of Style's guidance on dates)
  • other unacceptable date formats listed in MOS:BADDATEFORMAT
  • more than one date in a date-holding parameter
  • years before 100 AD, including BCE/BC dates. Try using parameter |orig-date= instead.

See Help: Citation Style 1 for information about limitations in the CS1 citation templates' handling of date formats. The MOS section on date ranges describes how to separate dates in a date range. Do not use &nbsp;, &ndash;, or {{spaced ndash}} as these corrupt the metadata. To add an en dash, use the CharInsert edit tool or see Wikipedia:How to make dashes. You may also use this one: –. A bot is often able to correct the separator, provided the overall format is unambiguous.

Future dates in |date= in CS1|2 citations are limited to current year + 1; that is, for 2020, citation dates in 2021 are acceptable but citation dates in 2022 and beyond are not.

Dates prior to 1582 are treated as Julian calendar dates. Dates from 1582 onward are treated as Gregorian calendar dates. The Julian calendar was used in some places until approximately 1923. Three Julian calendar dates in the overlap period, 29 February in the years 1700, 1800, and 1900, will cause this error message because those years are not leap years in the Gregorian calendar.

The access date (in |access-date=) is checked to ensure that it contains a full date (day, month, and year) and is between 15 January 2001 (the founding date of Wikipedia) and today's date plus one day, because it represents the date that an editor viewed a web-based source to verify a statement on Wikipedia. Because editors may be in time zones that are one day ahead of the UTC date, one extra day is accepted.

Pages with this error are automatically placed in Category:CS1 errors: dates (14,282 pages).[a]

Examples of unacceptable dates and how to fix them
Issue Unacceptable Acceptable
Hyphen in date range (use en dash) |date=2002-2003 |date=20022003
Slash in date range (use en dash) |date=2002/2003 or |date=July/August 2003 |date=20022003 or |date=JulyAugust 2003
Hyphen in date range (use en dash) |date=April-May 2004 |date=AprilMay 2004
Missing space around en dash for range of full dates |date=April 2003May 2004 |date=April 2003 May 2004
Month capitalization |date=28 february 1900 |date=28 February 1900
Month capitalization |date=28 FEBRUARY 1900 |date=28 February 1900
Season capitalization |date=spring 2011 |date=Spring 2011
Future date (typo) |date=2102 |date=2012
Access date in future (see note above) |access-date=October 21, 2020 |access-date=October 19, 2020
Access date impossibly far in the past (typo) |access-date=1 January 2001 |access-date=1 January 2010
Access date only specifies month |access-date=January 2015 |access-date=12 January 2015
Ambiguous date range or year and month |date=2002-03
  • |date=2002–2003
  • |date=March 2002
Bad abbreviation |date=Febr. 28, 1900
  • |date=Feb 28, 1900
  • |date=February 28, 1900
Nonexistent date |date=February 29, 1900
Undated |date=Undated |date=n.d.
Comma in month and year |date=February, 1900 |date=February 1900
Comma in season |date=Winter, 1900–1901 |date=Winter 1900–1901
Missing comma in format which requires it |date=February 28 1900 |date=February 28, 1900 or |date=28 February 1900
Non-date text |date=2008, originally 2000 |date=2008 |orig-date=2000
Zero-padding |date=January 04, 1987 |date=January 4, 1987
Date with slashes |date=12/6/87
  • |date=December 6, 1987
  • |date=12 June 1987
Two-digit year |date=87-12-06 |date=1987-12-06
One-digit month or day |date=2007-3-6 |date=2007-03-06
Wikified date |date=[[April 1]], [[1999]] |date=April 1, 1999
"mm-dd-yyyy" or "dd-mm-yyyy" date format |date=07-12-2009 |date=7 December 2009 or |date=12 July 2009
or
|date=July 12, 2009 or |date=December 7, 2009
Approximate or uncertain dates |date=circa 1970 or |date={{circa}} 1970 |date=c. 1970

Check |doi= value

Check |doi= value

When Citation Style 1 and Citation Style 2 templates contain |doi=, a test is done to see if the prefix portion of the DOI value is correctly formatted and has what appears to be a valid registrant code. A proper DOI prefix begins with the 10. directory indicator. The remaining portion of the prefix is a string of digits and the dot character which form the registrant code. When the directory indicator is 10., the CS1|2 templates test for a valid registrant code. Valid registrant codes:

  • must be composed of digits
  • must be in the range:
    • 1000–9999
    • 10000–49999
  • may have one or more subcodes that begin with a dot followed by digits (1000.10)
  • must not be 5555 (invalid/temporary/test)

Additionally, the |doi= value is checked to make sure that it does not contain spaces, en dashes, does not end with punctuation. Further validation of the DOI is not performed.

Do not include the https://doi.org/ scheme and domain name from a URL. A proper |doi= value looks like |doi=10.1103/PhysRevLett.80.904.

To resolve this error, ensure that the |doi= value is correct.

In very rare cases, publishers have released works with a DOI deviating from the standard form. If you are certain that such a non-conforming DOI truly corresponds to the published work, then you can add accept-this-as-written markup around the identifier to suppress the error message. (Do not use this markup for DOIs, which are inactive rather than non-conforming. Instead, use |doi-broken-date= for them.)

Pages with this error are automatically placed in Category:CS1 errors: DOI.[a]

Check |hdl= value

Check |hdl= value

When Citation Style 1 and Citation Style 2 templates contain |hdl=, a test is done to see if the hdl value looks like a properly defined value. The |hdl= value is checked to make sure that it does not contain spaces or en dashes and does not end with punctuation. Further validation of the hdl is not performed.

To resolve this error, ensure that the |hdl= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: HDL.[a]

Check |isbn= value

Check |isbn= value: <type>

Citation Style 1 and Citation Style 2 templates that contain |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 |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 |id={{ISBN|...}} instead.)

The error message <type> indicator can be:

length – ISBN is not 10 or 13 digits
checksum – ISBN has one or more incorrect digits; look for typos and transposition
invalid character – ISBN has one or more 'digits' that is not in the allowed set appropriate to ISBN length
invalid prefix – 13-digit ISBNs must begin with '978' or '979'
invalid form – 10-digit ISBNs with the mis-positioned 'X' character
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 |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 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 |isbn= that appear to be legitimate – length is right, check digit is correct – but that aren't true ISBN numbers. This tool may be helpful.

See also Wikipedia:ISBN.

Pages with this error are automatically placed in Category:CS1 errors: ISBN.[a]

Check |ismn= value

Check |ismn= value

Citation Style 1 and Citation Style 2 templates that contain |ismn= are checked to ensure that the ISMN is the proper length (thirteen digits), that the ISMN uses the correct optional separators (simple space or hyphen), and that the final check digit is correct according to the ISMN specification. Only one ISMN is allowed in this field because the whole |ismn= value is included in the citation's COinS metadata. See also Wikipedia:COinS. More than one ISMN, or characters that are not part of the ISMN, corrupt the COinS metadata. (If relevant, they can be specified using |id={{ISMN|...}} instead.)

To resolve this error, ensure that the |ismn= value is correct, that only one ISMN is used, that the proper optional separators are used, and that no other text is included. Make sure that the ISMN contains exactly 13 digits.

Pages with this error are automatically placed in Category:CS1 errors: ISMN.[a]

Check |issn= value

Citation Style 1 and Citation Style 2 templates that contain |issn= and/or |eissn= are checked to ensure that the ISSN is the proper length (eight digits) and that the final check digit validates according to the ISSN specification. Only one each of ISSN and eISSN is allowed in this field because the whole |issn= and |eissn= values are included in the citation's COinS metadata. See also Wikipedia:COinS. (If relevant, they can be specified using |id={{ISSN|...}} {{EISSN|...}} instead.)

The ISSN and eISSN are always rendered as two four-digit numbers separated with a hyphen.

To resolve this error, ensure that the |issn= and |eissn= values are correct, that only one value per parameter is used, and that no other text is included (allowable characters are 0–9, X, and -). If the check-digit is a lowercase 'x', change it to an uppercase 'X'.

In very rare cases, publishers have released works with a malformed identifier. If you are certain that a non-conforming identifier truly corresponds to the published work, then you can add accept-this-as-written markup around the identifier to suppress the error message. In some cases, works may have been reissued with a corrected identifier. Use the corrected one when possible.

Pages with this error are automatically placed in Category:CS1 errors: ISSN.[a]

Check |jfm= value

Check |jfm= value

When Citation Style 1 and Citation Style 2 templates contain |jfm=, a test is done to see if the JFM identifier value looks like a properly defined value. The |jfm= identifier is checked to make sure that it has the form: nn.nnnn.nn where n is any digit 0–9. Further validation of the JFM identifier is not performed.

To resolve this error, ensure that the |jfm= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: JFM.[a]

Check |lccn= value

Check |lccn= value

The |lccn= parameter is the Library of Congress Control Number identifier. It is checked to ensure that the identifier is the proper length and has the correct initial digits.

LCCN is a character string 8–12 characters long. The length of the LCCN dictates the character type of the initial 1–3 characters; the rightmost eight are always digits.[5]

LCCN format description
Length Description
8 all characters are digits
9 first character is a lower case letter
10 first two characters are either both lower case letters or both digits
11 first character is a lower case letter, second and third characters are either both lower case letters or both digits
12 first two characters are both lower case letters

Further validation is not performed.

To resolve this error, ensure that the |lccn= value is correct and that there are no other letters, punctuation, or other characters.

When receiving this error, be on the lookout for publishers who omitted leading zeros in the LCCN following the two or four digit year. For example, an LCCN that is properly 92-035427 could be shortened in the printed work to 92-35247. When experimenting with inserting omitted zeroes, cross-check the finished number against the LCCN permalinks online.

Pages with this error are automatically placed in Category:CS1 errors: LCCN.[a]

Check |message-id= value

Check |message-id= value

The |message-id= parameter holds the unique identifier associated with a netnews message.[6] The value in |message-id= is checked to make sure that it contains @ between left and right identifiers. |message-id= is also checked to make sure that the first character is not < and the last character is not >. Module:Citation/CS1 adds the URI scheme news: to the value in |message-id=. If the value in |message-id= is wrapped in <...> characters, the link created fails.

Further validation is not performed.

To resolve this error, ensure that the |message-id= value is correct, that it contains @ and is not wrapped in <...> characters.

Pages with this error are automatically placed in Category:CS1 errors: message-id.[a]

Check |mr= value

Check |mr= value

When Citation Style 1 and Citation Style 2 templates contain |mr=, a test is done to see if the MR identifier value looks like a properly defined value. The |mr= identifier is checked to make sure that it contains only digits and that it is no more than seven digits in length. Further validation of the MR identifier is not performed.

To resolve this error, ensure that the |mr= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: MR.[a]

Check |oclc= value

Check |oclc= value

The |oclc= parameter is the OCLC identifier. Only a single OCLC identifier is allowed. (If relevant, multiple OCLCs can be specified using |id={{OCLC|...}} instead.)

The identifier must be in one of these forms:

  1. prefix ocm followed by 8 digits
  2. prefix ocn followed by 9 digits
  3. prefix on followed by 10 digits
  4. prefix (OCoLC) followed by a variable number of digits without leading zeros
  5. 1 to 10 digits without prefix

Further validation is not performed.

To resolve this error, ensure that the |oclc= value is correct.

A tip for fixing this error: Editors sometimes place valid ISBN, LCCN, ASIN, or other identifiers in |oclc=.

Pages with this error are automatically placed in Category:CS1 errors: OCLC.[a]

Check |ol= value

Check |ol= value

The |ol= parameter is the Open Library identifier. The identifier is one or more digits followed by a last character that is either A (authors), M (books), or W (works). Further validation is not performed.

To resolve this error, ensure that the |ol= value is correct. Do not include "OL" in the value.

Pages with this error are automatically placed in Category:CS1 errors: OL.[a]

Check |-link= value

These link-holding parameters and their matching title-holding parameters are combined to create a working wikilink to a related article.

  • |author-link=
  • |contributor-link=
  • |editor-link=
  • |episode-link=
  • |interviewer-link=
  • |series-link=
  • |subject-link=
  • |title-link=
  • |translator-link=
  • |author=
  • |contributor=
  • |editor=
  • |episode=
  • |interviewer=
  • |series=
  • |subject=
  • |title=
  • |translator=

(Parameters checked for this error may also be of the form |author-linkn= or |authorn-link=.)

This error occurs when any of these |<param>-link= parameters contain a wikilink or a URL, or they contain any of the characters not permitted in Wikipedia article titles per WP:TITLESPECIALCHARACTERS (except _ (underscore), used as a replacement for spaces, and #, used as a fragment identifier when linking to article sections). The prohibited characters are: < > [ ] | { }.

The |<param>-link= parameter value should contain only the title of a Wikipedia article or a link to a section of a Wikipedia article. Module:Citation/CS1 checks the |<param>-link= parameter values for wikimarkup and for a URI scheme (http://, https://, the protocol relative scheme //, etc.). Interlanguage links in any of the |<param>-link= parameters require a leading colon:

:fr:Période d'exil de Caravage

While primarily intended to catch the errors mentioned above, Module:Citation/CS1 will also catch malformed interlanguage wikilinks wherever they occur. Interlanguage wikilinks that have the form:

[[fr:Période d'exil de Caravage]]

do not create visible clickable links in the article text. Instead, these links appear in the left pane in the languages list. Module:Citation/CS1 disables interlanguage links in this form and emits an error message. The correct form is:

[[:fr:Période d'exil de Caravage]]

This error can also be caused when there is a |<param>-link= value and the matching |<param>= parameter contains a wikilink.

To resolve this error, do one of the following:

  • Ensure that the |<param>-link= value is the full name of a Wikipedia article (without brackets) or a section of an article, and not a link to an external web site.
  • Make sure that there are no wikilinks in the matching |<param>= parameters.
  • If you want to link to a URL outside of Wikipedia, move the link to |url= or a similar parameter, if one is available in the template you are using.

Pages with this error are automatically placed in Category:CS1 errors: parameter link.[a]

Check |pmc= value

Check |pmc= value

The |pmc= parameter is the PubMed Central identifier. PMCs are sequential numbers beginning at 1 and counting up. Module:Citation/CS1 checks the PMC identifier to make sure that the value is a number greater than zero and less than 8000000 and that the identifier contains only digits. Further validation is not performed.

To resolve this error, ensure that the |pmc= value is correct, and that there are no letters, punctuation, or other characters. Do not include "PMC" in the value.

Pages with this error are automatically placed in Category:CS1 errors: PMC.[a]

Check |pmid= value

Check |pmid= value

The |pmid= parameter is the PubMed identifier. PMIDs are checked to ensure that the identifier is a simple number without punctuation or spaces with a value between 1 and 33100000. Further validation is not performed.

To resolve this error, ensure that the |pmid= value is correct. If you find something that looks like a PMID and begins with "PMC", use |pmc= instead of |pmid=.

Pages with this error are automatically placed in Category:CS1 errors: PMID.[a]

Check |sbn= value

Check |sbn= value

Citation Style 1 and Citation Style 2 templates that contain |sbn= are checked to ensure that the SBN is the proper length (nine digits), that the SBN uses the correct optional separators (simple space or hyphen), and that the final check digit is correct according to the SBN specification. Only one SBN is allowed in this field because the whole |sbn= value is included in the citation's COinS metadata. See also Wikipedia:COinS. More than one SBN, or characters that are not part of the SBN, corrupt the COinS metadata and may also corrupt the link to Special:BookSources.

The error message <type> indicator can be:

length – SBN is not 9 digits
checksum – SBN has one or more incorrect digits; look for typos and transposition
invalid character – SBN has one or more 'digits' that is not in the allowed set
invalid form – mis-positioned 'X' check digit

To resolve this error, ensure that the |sbn= value is correct, that only one SBN is used, that the proper optional separators are used, and that no other text is included. 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 SBN 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 the SBN as printed in your source is refusing to validate, do check both the front matter and the book cover for SBNs. It is not uncommon for the SBN to be misprinted in the front matter but correct on the cover.
  • Do preview your edit and check that the new SBN does now link to the correct source.

In very rare cases, publishers have released books with malformed SBNs. If you are certain that a non-conforming SBN truly corresponds to the published work, then you can add accept-this-as-written markup around the identifier to suppress the error message. In many cases, books may have been reissued with a corrected SBN. Use a corrected SBN when possible.

Pages with this error are automatically placed in Category:CS1 errors: SBN.[a]

Check |ssrn= value

Check |ssrn= value

The |ssrn= parameter is the Social Science Research Network identifier. SSRNs are checked to ensure that the identifier is a simple number without punctuation or spaces with a value between 100 and 4000000. Further validation is not performed.

To resolve this error, ensure that the |ssrn= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: SSRN.[a]

Check |s2cid= value

Check |s2cid= value

The |s2cid= parameter is the Semantic Scholar corpus identifier. S2CIDs are checked to ensure that the identifier is a simple number without punctuation or spaces with a value between 1 and 230000000. Further validation is not performed.

To resolve this error, ensure that the |s2cid= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: S2CID.[a]

Check |url= value

Check |url= value

External links in Citation Style 1 and Citation Style 2 templates are made from two parts: the title (|title=, |chapter=, etc.) and the URL (|url=, |archive-url=, |chapter-url=, |lay-url=, etc.). The |url= parameter and other URL parameters must begin with a supported URI scheme. The URI schemes http://, https:// and the protocol relative scheme // are most commonly used; irc://, ircs://, ftp://, news:, mailto: and gopher:// are also supported.

The URL field is checked to ensure that it contains only Latin characters and does not contain spaces. The URL may be protocol relative (begins with //). If there are no spaces and the URL is not protocol relative, then the scheme must comply with RFC 3986.[7]

Top- and second-level domain names are checked for proper form. Generally, top-level domain names must be two or more letters; second-level domain names must be two or more letters, digits, or hyphens (first and last character must be a letter or digit). Single-letter second-level domains are supported for:

  • all cc TLDs (the country code is not validated)
  • the .org TLD
  • certain letters of the .com TLD (q, x, z)
  • certain letters of the .net TLD (i, q)

Third- and subsequent-level domain names are not checked. The path portion of the URL is not checked.

To resolve this error, ensure that |url= and other URL parameters contain valid URLs. Online tools are available to internationalize URLs that are written in non-Latin scripts:

  • "IDN Conversion Tool". Verisign.

Pages with this error are automatically placed in Category:Pages with URL errors.[a]

Check |zbl= value

Check |zbl= value

When Citation Style 1 and Citation Style 2 templates contain |zbl=, a test is done to see if the Zbl identifier value looks like a properly defined value. The |zbl= identifier is checked to make sure that it has the form: nnnn.nnnnn where n is any digit 0–9. Up to three leading zeros in the first quartet may be omitted. Further validation of the Zbl identifier is not performed.

To resolve this error, ensure that the |zbl= value is correct.

Pages with this error are automatically placed in Category:CS1 errors: ZBL.[a]

|biorxiv= required

|biorxiv= required

{{cite bioRxiv}} requires the identifier parameter |biorxiv=.

To resolve this error, ensure that the template has |biorxiv= with a properly constructed value.

Pages with this error are automatically placed in Category:CS1 errors: bioRxiv.[a]

Cite has empty unknown parameter:

Cite has empty unknown parameter: <param>

This error message is hidden. To show this error message see Controlling error message display.

This error message highlights CS1|2 templates that hold empty parameters with names that are not known to CS1|2. This error message is a companion to Unknown parameter |xxxx= ignored.

Empty positional parameters, which typically look like two adjacent pipes in a template, | |, or a pipe and then the end of the template, |}}, are identified as numbered parameters: |1=. Parameters that have both a pipe and an equal sign but do not have a name are identified as empty string parameters: |= or | =|(empty string)=. Various templates that wrap CS1|2 templates may cause this error when they use constructs like this: |{{#if:{{{2|}}}|title}}={{{2|}}}. When {{{2|}}} does not have a value, the template creates |=.

To resolve this error, remove the extra pipe, correct the parameter name, or remove the parameter from the CS1|2 template.

Pages with this error are automatically placed in Category:CS1 errors: empty unknown parameters.[a]

Cite