Help:Cite errors/Cite error references duplicate key

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• For basic information on the footnotes system, see Referencing for beginners; for advanced help, see Footnotes.

Sfn

If two or more calls to {{sfn}} use the same citation parameters, that is, if the author(s), year, and page number(s) are all identical, but there is some other difference, such as a use of pp= vs p=, or a use of ps= in one but not the other, this issue will arise.

The solution is to make the calls identical. If the ps= parameter was being used to include a quote or other extended content, use {{harvnb}} inside a <ref>...</ref> construct with the quote after the template but inside the ref tag structure.

Nested footnotes

If there are nested footnotes, i.e. a reference within another reference, then the error can occur even if two definitions have identical text. Example where {{sfn}} will create a ref name with another reference inside it:

<ref name="Buna">Advance to Buna</ref>
{{sfn|Blakeley|1956|ps=. Cited in Advance to Buna.<ref name=Buna />}}
{{sfn|Blakeley|1956|ps=. Cited in Advance to Buna.<ref name=Buna />}}

Removing the inner reference will fix the error.

Technical

Pages with this error message are placed into Pages with duplicate reference names. The system message page is at Cite error references duplicate key.

Templates

Tracked in Phabricator
Task T39256

In order to include variable data within a reference tag such as <ref ref_content name=ref_name>, the #tag parser function must be used. Currently #tag only supports balanced tags, not a singular tag, thus <tag_type element /> cannot normally be used in a template unless the element is hard coded.

However, Cite has been modified since 2008 to treat <ref name="ref-foo"></ref> identically to <ref name="ref-foo" />. Note that there cannot be even a space between the <ref . . .> and the </ref>, otherwise this will result in definition of the reference named "ref-foo" to be " ", which if meant to be second reference by name to an existing reference will cause a duplicate definition error. Correct code to produce a singular tag will look like {{#tag:ref ||name={{{parameter}}}}}, that is, no space between the two "|"s.