Wikipedia:Citing sources (WP:DEADREF)

A citation, also called a reference, uniquely identifies a source of information, e.g.:  Wikipedia's verifiability policy requires inline citations for any material challenged or likely to be challenged, and for all quotations, anywhere in article space. A citation or reference in an article usually has two parts. In the first part, each section of text that is either based on, or quoted from, an outside source is marked as such with an inline citation. The inline citation will be a superscript footnote number. The second necessary part of the citation or reference is the list of full references, which provides complete, formatted detail about the source, so that anyone reading the article can find it and verify it. This page explains how to place and format both parts of the citation. Each article should use one citation method or style throughout. If an article already has citations, preserve consistency by using that method or seek consensus on the talk page before changing it (the principle is reviewed at § Variation in citation methods). While you should try to write citations correctly, what matters most is that you provide enough information to identify the source. Others will improve the formatting if needed. See: "Help:Referencing for beginners", for a brief introduction on how to put references in Wikipedia articles; and cite templates in Visual Editor, about a graphical way for citation, included in Wikipedia.  An inline citation means any citation added close to the material it supports, for example after the sentence or paragraph, normally in the form of a footnote. In-text attribution involves adding the source of a statement to the article text, such as Rawls argues that X.[5] This is done whenever a writer or speaker should be credited, such as with quotations, close paraphrasing, or statements of opinion or uncertain fact. The in-text attribution does not give full details of the source – this is done in a footnote in the normal way. See In-text attribution below. A general reference is a citation that supports content, but is not linked to any particular piece of material in the article through an inline citation. General references are usually listed at the end of the article in a References section. They are usually found in underdeveloped articles, especially when all article content is supported by a single source. They may also be listed in more developed articles as a supplement to inline citations.   === Short and full citations ===  A full citation fully identifies a reliable source and, where applicable, the place in that source (such as a page number) where the information in question can be found. For example: Rawls, John. A Theory of Justice. Harvard University Press, 1971, p. 1. This type of citation is usually given as a footnote, and is the most commonly used citation method in Wikipedia articles.A short citation is an inline citation that identifies the place in a source where specific information can be found, but without giving full details of the source. Some Wikipedia articles use it, giving summary information about the source together with a page number. For example, <ref>Rawls 1971, p. 1.</ref>, which renders as Rawls 1971, p. 1.. These are used together with full citations, which are listed in a separate "References" section or provided in an earlier footnote.Forms of short citations used include author-date referencing (APA style, Harvard style, or Chicago style), and author-title or author-page referencing (MLA style or Chicago style). As before, the list of footnotes is automatically generated in a "Notes" or "Footnotes" section, which immediately precedes the "References" section containing the full citations to the source. Short citations can be written manually, or by using either the {{sfn}} or {{harvnb}} templates or the {{r}} referencing template. (Note that templates should not be added without consensus to an article that already uses a consistent referencing style.) The short citations and full citations may be linked so that the reader can click on the short note to find full information about the source. See the template documentation for details and solutions to common problems. For variations with and without templates, see wikilinks to full references. For a set of realistic examples, see these. This is how short citations look in the edit box:  The Sun is pretty big,<ref>Miller 2005, p. 23.</ref> but the Moon is not so big.<ref>Brown 2006, p. 46.</ref> The Sun is also quite hot.<ref>Miller 2005, p. 34.</ref>  == Notes == {{reflist}}  == References == * Brown, Rebecca (2006). "Size of the Moon", ''Scientific American'', 51 (78). * Miller, Edward (2005). ''The Sun''. Academic Press.  This is how they look in the article:  The Sun is pretty big, but the Moon is not so big. The Sun is also quite hot.Notes  References  Brown, Rebecca (2006). "Size of the Moon", Scientific American, 51 (78). Miller, Edward (2005). The Sun. Academic Press. Shortened notes using titles rather than publication dates would look like this in the article:  Notes  When using manual links it is easy to introduce errors such as duplicate anchors and unused references. The script User:Trappist the monk/HarvErrors will show many related errors. Duplicate anchors may be found by using the W3C Markup Validation Service.  By citing sources for Wikipedia content, you enable users to verify that the information given is supported by reliable sources, thus improving the credibility of Wikipedia while showing that the content is not original research. You also help users find additional information on the subject; and by giving attribution you avoid plagiarising the source of your words or ideas. In particular, sources are required for material that is challenged or likely to be challenged – if reliable sources cannot be found for challenged material, it is likely to be removed from the article. Sources are also required when quoting someone, with or without quotation marks, or closely paraphrasing a source. However, the citing of sources is not limited to those situations – editors are always encouraged to add or improve citations for any information contained in an article. Citations are especially desirable for statements about living persons, particularly when the statements are contentious or potentially defamatory. In accordance with the biography of living persons policy, unsourced information of this type is likely to be removed on sight.   === Multimedia === For an image or other media file, details of its origin and copyright status should appear on its file page. Image captions should be referenced as appropriate just like any other part of the article. A citation is not needed for descriptions such as alt text that are verifiable directly from the image itself, or for text that merely identifies a source (e.g., the caption "Belshazzar's Feast (1635)" for File:Rembrandt-Belsazar.jpg).   === When not to cite ===  Citations are not used on disambiguation pages (sourcing for the information given there should be done in the target articles). Citations are often omitted from the lead section of an article, insofar as the lead summarizes information for which sources are given later in the article, although quotations and controversial statements, particularly if about living persons, should be supported by citations even in the lead. See WP:LEADCITE for more information.  Inline citations allow the reader to associate a given piece of material in an article with the specific reliable source(s) that support it. Inline citations are added using footnotes, long or short.    === How to place an inline citation using ref tags ===  To create a footnote, use the <ref>...</ref> syntax at the appropriate place in the article text, for example:  Justice is a human invention.<ref>Rawls, John. ''A Theory of Justice''. Harvard University Press, 1971, p. 1.</ref> It ...which will be displayed as something like:  Justice is a human invention.[1] It ...It will also be necessary to generate the list of footnotes (where the citation text is actually displayed); for this, see the previous section. As in the above example, citation markers are normally placed after adjacent punctuation such as periods (full stops) and commas. For exceptions, see the WP:Manual of Style § Punctuation and footnotes. Note also that no space is added before the citation marker. Citations should not be placed within, or on the same line as, section headings. The citation should be added close to the material it supports, offering text–source integrity. If a word or phrase is particularly contentious, an inline citation may be added next to that word or phrase within the sentence, but it is usually sufficient to add the citation to the end of the clause, sentence, or paragraph, so long as it's clear which source supports which part of the text.   ==== Avoiding clutter ====  Inline references can significantly bloat the wikitext in the edit window and can become difficult to manage and confusing. There are two main methods to avoid clutter in the edit window:  Using list-defined references by collecting the full citation code within the reference list template {{reflist}}, and then inserting them in the text with a shortened reference tag, for example <ref name="Smith 2001, p99" />. Inserting short citations (see below) that then refer to a full list of source textsAs with other citation formats, articles should not undergo large-scale conversion between formats without consensus to do so. Note, however, that references defined in the reference list template can no longer be edited with the VisualEditor.   ==== Repeated citations ====  For multiple use of the same inline citation or footnote, you can use the named references feature, choosing a name to identify the inline citation, and typing <ref name="name">text of the citation</ref>. Thereafter, the same named reference may be reused any number of times either before or after the defining use by typing the previous reference name, like this: <ref name="name" />. The use of the slash before the > means that the tag is self-closing, and the </ref> used to close other references must not be used in addition. The text of the name can be almost anything‍—‌apart from being completely numeric. If spaces are used in the text of the name, the text must be placed within double quotes. Placing all named references within double quotes may be helpful to future editors who do not know that rule. To help with page maintenance, it is recommended that the text of the name have a connection to the inline citation or footnote, for example "author year page": <ref name="Smith 2005 p94">text of the citation</ref>. Use straight quotation marks " to enclose the reference name. Do not use curly quotation marks “”. Curly marks are treated as another character, not as delimiters. The page will display an error if one style of quotation marks is used when first naming the reference, and the other style is used in a repeated reference, or if a mix of styles is used in the repeated references.   ==== Citing multiple pages of the same source ====  When an article cites many different pages from the same source, to avoid the redundancy of many big, nearly identical full citations, most Wikipedia editors use one of these options:  Named references in conjunction with a combined list of page numbers using the |pages= parameter of the {{cite}} templates (most commonly used, but can become confusing for large number of pages) Named references in conjunction with the {{rp}} or {{r}} templates to specify the page Short citationsThe use of ibid., id., or similar abbreviations is discouraged, as they may become broken as new references are added (op. cit. is less problematic in that it should refer explicitly to a citation contained in the article; however, not all readers are familiar with the meaning of the terms). If the use of ibid is extensive, tag the article using the {{ibid}} template.   === What information to include ===  Listed below is the information that a typical inline citation or general reference will provide, though other details may be added as necessary. This information is included in order to identify the source, assist readers in finding it, and (in the case of inline citations) indicate the place in the source where the information is to be found. (If an article uses short citations, then the inline citations will refer to this information in abbreviated form, as described in the relevant sections above.)   === Examples ===   ==== Books ====  Citations for books typically include:  name of author(s) title of book volume when appropriate name of publisher place of publication date of publication of the edition chapter or page numbers cited, if appropriate edition, if not the first edition ISBN (optional)Citations for individually authored chapters in books typically include:  name of author(s) title of the chapter name of book's editor name of book and other details as above chapter number or page numbers for the chapter (optional)In some instances, the verso of a book's title page may record, "Reprinted with corrections XXXX" or similar, where 'XXXX' is a year. This is a different version of a book in the same way that different editions are different versions. In such a case, record: the year of the particular reprint, the edition immediately prior to this particular reprint (if not the first edition) and a note to say "Reprint with corrections". If {{cite}} (or similar) is being used, the notation, "Reprint with corrections", can be added immediately following the template. § Dates and reprints of older publications gives an example of appending a similar textual note.   ==== Journal articles ====  Citations for journal articles typically include:  name of the author(s) year and sometimes month of publication title of the article name of the journal volume number, issue number, and page numbers (article numbers in some electronic journals) DOI and/or other identifiers are optional and can often be used in place of a less stable URL (although URLs may also be listed in a journal citation)   ==== Newspaper articles ====  Citations for newspaper articles typically include:  byline (author's name), if any title of the article name of the newspaper in italics city of publication (if not included in name of newspaper) date of publication page number(s) are optional and may be substituted with negative number(s) on microfilm reels   ==== Web pages ====  Citations for World Wide Web pages typically include:  URL of the specific web page where the referenced content can be found name of the author(s) title of the article title or domain name of the website publisher, if known date of publication page number(s) (if applicable) the date you retrieved (or accessed) the web page (required if the publication date is unknown)   ==== Sound recordings ====  Citations for sound recordings typically include:  name of the composer(s), songwriter(s), script writer(s) or the like name of the performer(s) title of the song or individual track title of the album (if applicable) name of the record label year of release medium (for example: LP, audio cassette, CD, MP3 file) approximate time at which event or point of interest occurs, where appropriateDo not cite an entire body of work by one performer. Instead, make one citation for each work your text relies on.   ==== Film, television, or video recordings ====  Citations for films, TV episodes, or video recordings typically include:  name of the director name of the producer, if relevant names of major performers the title of a TV episode title of the film or TV series name of the studio year of release medium (for example: film, videocassette, DVD) approximate time at which event or point of interest occurs, where appropriate   ==== Wikidata ====   Wikidata is largely user-generated, and articles should not directly cite Wikidata as a source (just as it would be inappropriate to cite other Wikipedias' articles as sources).  Wikidata's statements, however, can be directly transcluded into articles; this is usually done to provide external links or infobox data. For example, more than two million external links from Wikidata are shown through the {{Authority control}} template. There has been controversy over the use of Wikidata in the English Wikipedia due to vandalism and its own sourcing. While there is no consensus on whether information from Wikidata should be used at all, there is general agreement that any Wikidata statements that are transcluded need to be just as – or more – reliable compared to Wikipedia content. As such, Module:WikidataIB and some related modules and templates filter Wikidata statements not supported by a reference by default; however, other modules and templates, such as Module:Wikidata, do not. In order to transclude an item from Wikidata, the QID (Q number) of an item in Wikidata needs to be known. QID can by found by searching for an item by the name or DOI in Wikidata. A book, a journal article, a musical recording, sheet music or any other item can be represented by a structured item in Wikidata. The {{Cite Q}} template can be used to cite works whose metadata is held in Wikidata, provided the cited work meets Wikipedia's standards. As of December 2020, {{Cite Q}} does not support "last, first" or Vancouver-style author name lists, so it should not be used in articles in which "last, first" or Vancouver-style author names are the dominant citation style.   ==== Other ==== See also:  {{cite album notes}} {{cite comic}} {{comic strip reference}} {{cite conference}} for conference reports or papers {{cite court}} for court cases or legal decisions {{cite act}} for a law or legal act {{cite encyclopedia}} {{cite episode}} for TV or radio series {{cite mailing list}} {{cite map}} {{cite newsgroup}} {{cite patent}} for patents {{cite press release}} {{cite report}} {{cite thesis}} {{cite video game}}   === Identifying parts of a source ===  When citing lengthy sources, you should identify which part of a source is being cited.   ==== Books and print articles ==== Specify the page number or range of page numbers. Page numbers are not required for a reference to the book or article as a whole. When you specify a page number, it is helpful to specify the version (date and edition for books) of the source because the layout, pagination, length, etc. can change between editions. If there are no page numbers, whether in ebooks or print materials, then you can use other means of identifying the relevant section of a lengthy work, such as the chapter number or the section title. In some works, such as plays and ancient works, there are standard methods of referring to sections, such as "Act 1, scene 2" for plays and Bekker numbers for Aristotle's works. Use these methods whenever appropriate.   ==== Audio and video sources ==== Specify the time at which the event or other point of interest occurs. Be as precise as possible about the version of the source that you are citing; for example, movies are often released in different editions or "cuts". Due to variations between formats and playback equipment, precision may not be accurate in some cases. However, many government agencies do not publish minutes and transcripts but do post video of official meetings online; generally the subcontractors who handle audio-visual are quite precise.   === Links and ID numbers === A citation ideally includes a link or ID number to help editors locate the source. If you have a URL (web page) link, you can add it to the title part of the citation, so that when you add the citation to Wikipedia the URL becomes hidden and the title becomes clickable. To do this, enclose the URL and the title in square brackets—the URL first, then a space, then the title. For example:  For web-only sources with no publication date, the "Retrieved" date (or the date you accessed the web page) should be included, in case the web page changes in the future. For example: Retrieved 15 July 2011 or you can use the access-date parameter in the automatic Wikipedia:refToolbar 2.0 editing window feature. You can also add an ID number to the end of a citation. The ID number might be an ISBN for a book, a DOI (digital object identifier) for an article or some e-books, or any of several ID numbers that are specific to particular article databases, such as a PMID number for articles on PubMed. It may be possible to format these so that they are automatically activated and become clickable when added to Wikipedia, for example by typing ISBN (or PMID) followed by a space and the ID number. If your source is not available online, it should be available in reputable libraries, archives, or collections. If a citation without an external link is challenged as unavailable, any of the following is sufficient to show the material to be reasonably available (though not necessarily reliable): providing an ISBN or OCLC number; linking to an established Wikipedia article about the source (the work, its author, or its publisher); or directly quoting the material on the talk page, briefly and in context.   ==== Linking to pages in PDF files ====  Links to long PDF documents can be made more convenient by taking readers to a specific page with the addition of #page=n to the document URL, where n is the page number. For example, using http://www.domain.com/document.pdf#page=5 as the citation URL displays page five of the document in any PDF viewer that supports this feature. If the viewer or browser does not support it, it will display the first page instead.   ==== Linking to Google Books pages ====  Google Books sometimes allows numbered book pages to be linked to directly. Page links should only be added when the book is available for preview; they will not work with snippet view. Keep in mind that availability varies by location. No editor is required to add page links, but if another editor adds them, they should not be removed without cause; see the October 2010 RfC for further information. These can be added in several ways (with and without citation templates):  Rawls, John. A Theory of Justice. Harvard University Press, 1971, p. 18. Or with a template: Rawls, John (1971). A Theory of Justice. Harvard University Press. p. 18. Rawls 1971, p. 18. Rawls 1971, p. 18. Rawls 1971, p. 18. Rawls 1971, 18.In edit mode, the URL for p. 18 of A Theory of Justice can be entered like this using the {{Cite book}} template:  {{cite book |last=Rawls |first=John |date=1971 |title=A Theory of Justice |url=https://books.google.com/books?id=kvpby7HtAe0C&pg=PA18 |publisher=Harvard University Press |page=18}} or like this, in the first of the above examples, formatted manually:  When the page number is a Roman numeral, commonly seen at the beginning of books, the URL looks like this for page xvii (Roman numeral 17) of the same book:     https://books.google.com/books?id=kvpby7HtAe0C&pg=PR17The &pg=PR17 indicates "page, Roman, 17", in contrast to the &pg=PA18, "page, Arabic, 18" the URL given earlier. You can also link to a tipped-in page, such as an unnumbered page of images between two regular pages. (If the page contains an image that is protected by copyright, it will be replaced by a tiny notice saying "copyrighted image".) The URL for eleventh tipped-in page inserted after page 304 of The Selected Papers of Elizabeth Cady Stanton and Susan B. Anthony, looks like this:     https://books.google.com/books?id=dBs4CO1DsF4C&pg=PA304-IA11The &pg=PA304-IA11 can be interpreted as "page, Arabic, 304; inserted after: 11".  Note that some templates properly support links only in parameters specifically designed to hold URLs like |url= and |archive-url= and that placing links in other parameters may not link properly or will cause mangled COinS metadata output. However, the |page= and |pages= parameters of all Citation Style 1/Citation Style 2 citation templates, the family of {{sfn}}- and {{harv}}-style templates, as well as {{r}}, {{rp}} and {{ran}} are designed to be safe in this regard as well.Wikipedia DOI and Google Books Citation Maker or Citer may be helpful. Users may also link the quotation on Google Books to individual titles, via a short permalink which ends with their related ISBN, OCLC or LCCN numerical code, e.g.: http://books.google.com/books?vid=ISBN0521349931, a permalink to the Google book with the ISBN code 0521349931. For further details, you may see How-to explanation on support.google.com.   === Say where you read it ===  "Say where you read it" follows the practice in academic writing of citing sources directly only if you have read the source yourself. If your knowledge of the source is secondhand—that is, if you have read Jones (2010), who cited Smith (2009), and you want to use what Smith (2009) said—make clear that your knowledge of Smith is based on your reading of Jones. When citing the source, write the following (this formatting is just an example):  John Smith (2009). Name of Book I Haven't Seen, Cambridge University Press, p. 99, cited in Paul Jones (2010). Name of Encyclopedia I Have Seen, Oxford University Press, p. 29. Or if you are using short citations:  Smith (2009), p. 99, cited in Jones (2010), p. 29. The same principle applies when indicating the source of images and other media files in an article. Note: The advice to "say where you read it" does not mean that you have to give credit to any search engines, websites, libraries, library catalogs, archives, subscription services, bibliographies, or other sources that led you to Smith's book. If you have read a book or article yourself, that's all you have to cite. You do not have to specify how you obtained and read it. So long as you are confident that you read a true and accurate copy, it does not matter whether you read the material using an online service like Google Books; using preview options at a bookseller's website like Amazon; through your library; via online paid databases of scanned publications, such as JSTOR; using reading machines; on an e-reader (except to the extent that this affects page numbering); or any other method.   === Dates and reprints of older publications === Editors should be aware that older sources (especially those in the public domain) are sometimes reprinted with modern publication dates. When this occurs and the citation style being used requires it, cite both the original publication date, as well as the date of the re-publication, e.g.:  Darwin, Charles (1964) [1859]. On the Origin of Species (facsimile of 1st ed.). Harvard University Press.This is done automatically in the {{citation}} and {{cite book}} templates when you use the |orig-date= parameter. Alternately, information about the reprint can be appended as a textual note:  Boole, George (1854). An Investigation of the Laws of Thought on Which Are Founded the Mathematical Theories of Logic and Probabilities. Macmillan. Reprinted with corrections, Dover Publications, New York, NY, 1958.   === Seasonal publication dates and differing calendar systems === Publication dates, for both older and recent sources, should be written with the goal of helping the reader find the publication and, once found, confirm that the correct publication has been located. For example, if the publication date bears a date in the Julian calendar, it should not be converted to the Gregorian calendar. If the publication date was given as a season or holiday, such as "Winter" or "Christmas" of a particular year or two-year span, it should not be converted to a month or date, such as July–August or December 25. If a publication provided both seasonal and specific dates, prefer the specific one.   === Additional annotation ===  In most cases it is sufficient for a citation footnote simply to identify the source (as described in the sections above); readers can then consult the source to see how it supports the information in the article. Sometimes, however, it is useful to include additional annotation in the footnote, for example to indicate precisely which information the source is supporting (particularly when a single footnote lists more than one source – see § Bundling citations and § Text–source integrity, below). A footnote may also contain a relevant exact quotation from the source. This is especially helpful when the cited text is long or dense. A quotation allows readers to immediately identify the applicable portion of the reference. Quotes are also useful if the source is not easily accessible. In the case of non-English sources, it may be helpful to quote from the original text and then give an English translation. If the article itself contains a translation of a quote from such a source (without the original), then the original should be included in the footnote. (See the WP:Verifiability § Non-English sources policy for more information.)  This section describes how to add footnotes and also describes how to create a list of full bibliography citations to support shortened footnotes. The first editor to add footnotes to an article must create a dedicated citations' section where they are to appear. Any reasonable name may be chosen. The most frequent choice is "References". Other options in diminishing order of popularity are, "Notes", "Footnotes", or "Works cited", although these are more often used to distinguish between multiple end-matter sections or subsections. For an example of headings of a notes section, see the article Tezcatlipoca.   === General references ===  A general reference is a citation to a reliable source that supports content, but is not linked to any particular text in the article through an inline citation. General references are usually listed at the end of the article in a "References" section, and are usually sorted by the last name of the author or the editor. General reference sections are most likely to be found in underdeveloped articles, especially when all article content is supported by a single source. The disadvantage of general references is that text–source integrity is lost, unless the article is very short. They are frequently reworked by later editors into inline citations. The appearance of a general references section is the same as those given above in the sections on short citations and parenthetical references. If both cited and uncited references exist, their distinction can be highlighted with separate section names, e.g., "References" and "General references".   === How to create the list of citations ===  With some exceptions discussed below, citations appear in a single section containing only the <references /> tag or the {{Reflist}} template. For example:  == References == {{Reflist}}  The footnotes will then automatically be listed under that section heading. Each numbered footnote marker in the text is a clickable link to the corresponding footnote, and each footnote contains a caret that links back to the corresponding point in the text.  Scrolling lists, or lists of citations appearing within a scroll box, should never be used. This is because of issues with readability, browser compatibility, accessibility, printing, and site mirroring.If an article contains a list of general references, this is usually placed in a separate section, titled, for example, "References". This usually comes immediately after the section(s) listing footnotes, if any. (If the general references section is called "References", then the citations section is usually called "Notes".)   ==== Separating citations from explanatory footnotes ====  If an article contains both footnoted citations and other (explanatory) footnotes, then it is possible (but not necessary) to divide them into two separate lists using footnotes groups. The explanatory footnotes and the citations are then placed in separate sections, called (for example) "Notes" and "References" respectively. Another method of separating explanatory footnotes from footnoted references is using {{efn}} for the explanatory footnotes. The advantage of this system is that the content of an explanatory footnote can in this case be referenced with a footnoted citation. When explanatory footnotes and footnoted references are not in separate lists, {{refn}} can be used for explanatory footnotes containing footnoted citations.   ==== Duplicate citations ====  Combine precisely duplicated full citations, in keeping with the existing citation style (if any). In this context "precisely duplicated" means having the same content, not necessarily identical strings ("The New York Times" is the same as "NY Times"; different access-dates are not significant). Do not discourage editors, particularly inexperienced ones, from adding duplicate citations when the use of the source is appropriate, because a duplicate is better than no citation. But any editor should feel free to combine them, and doing so is the best practice on Wikipedia. Citations to different pages or parts of the same source can also be combined (preserving the distinct parts of the citations), as described in the previous section. Any method that is consistent with the existing citation style (if any) may be used, or consensus can be sought to change the existing style.  While citations should aim to provide the information listed above, Wikipedia does not have a single house style, though citations within any given article should follow a consistent style. A number of citation styles exist including those described in the Wikipedia articles for Citation, APA style, ASA style, MLA style, The Chicago Manual of Style, Author-date referencing, the Vancouver system and Bluebook. Although nearly any consistent style may be used, avoid all-numeric date formats other than YYYY-MM-DD, because of the ambiguity concerning which number is the month and which the day. For example, 2002-06-11 may be used, but not 11/06/2002. The YYYY-MM-DD format should in any case be limited to Gregorian calendar dates where the year is after 1582. Because it could easily be confused with a range of years, the format YYYY-MM (for example: 2002-06) is not used. For more information on the capitalization of cited works, see Wikipedia:Manual of Style/Capital letters § All caps and small caps.   === Variation in citation methods ===  Editors should not attempt to change an article's established citation style merely on the grounds of personal preference, to make it match other articles, or without first seeking consensus for the change.As with spelling differences, it is normal practice to defer to the style used by the first major contributor or adopted by the consensus of editors already working on the page, unless a change in consensus has been achieved. If the article you are editing is already using a particular citation style, you should follow it; if you believe it is inappropriate for the needs of the article, seek consensus for a change on the talk page. If you are the first contributor to add citations to an article, you may choose whichever style you think best for the article. However, since 5 September 2020, inline parenthetical referencing is a deprecated citation style on English-language Wikipedia. If all or most of the citations in an article consist of bare URLs, or otherwise fail to provide needed bibliographic data –  such as the name of the source, the title of the article or web page consulted, the author (if known), the publication date (if known), and the page numbers (where relevant) –  then that would not count as a "consistent citation style" and can be changed freely to insert such data. The data provided should be sufficient to uniquely identify the source, allow readers to find it, and allow readers to initially evaluate a source without retrieving it.   ==== Generally considered helpful ==== The following are standard practice:  improving existing citations by adding missing information, such as by replacing bare URLs with full bibliographic citations: an improvement because it aids verifiability, and fights link rot; replacing some or all general references with inline citations: an improvement because it provides more verifiable information to the reader, and helps maintain text–source integrity; imposing one style on an article with inconsistent citation styles (e.g., some of the citations in footnotes and others as parenthetical references): an improvement because it makes the citations easier to understand and edit; fixing errors in citation coding, including incorrectly used template parameters, and <ref> markup problems: an improvement because it helps the citations to be parsed correctly; combining duplicate citations (see § Duplicate citations, above). converting parenthetical referencing to an acceptable referencing style. replacing opaque named reference names with conventional ones, such as "Einstein-1905" instead of ":27".   ==== To be avoided ==== When an article is already consistent, avoid:  switching between major citation styles or replacing the preferred style of one academic discipline with another's – except when moving away from deprecated styles, such as parenthetical referencing; adding citation templates to an article that already uses a consistent system without templates, or removing citation templates from an article that uses them consistently; changing where the references are defined, e.g., moving reference definitions in the reflist to the prose, or moving reference definitions from the prose into the reflist.   ==== Parenthetical referencing ====  Since September 2020, inline parenthetical referencing has been deprecated on Wikipedia. This includes short citations in parentheses placed within the article text itself, such as (Smith 2010, p. 1). This does not affect short citations that use <ref> tags, which are not inline parenthetical references; see the section on short citations above for that method. As part of the deprecation process in existing articles, discussion of how best to convert inline parenthetical citations into currently accepted formats should be held if there is objection to a particular method. This is no longer in use:  As noted above under "What information to include", it is helpful to include hyperlinks to source material, when available. Here we note some issues concerning these links.   === Avoid embedded links ===  Embedded links to external websites should not be used as a form of inline citation, because they are highly susceptible to linkrot. Wikipedia allowed this in its early years—for example by adding a link after a sentence, like this: [http://media.guardian.co.uk/site/story/0,14173,1601858,00.html], which is rendered as: [1]. This is no longer recommended. Raw links are not recommended in lieu of properly written out citations, even if placed between ref tags, like this <ref>[http://media.guardian.co.uk/site/story/0,14173,1601858,00.html]</ref>. Since any citation that accurately identifies the source is better than none, do not revert the good-faith addition of partial citations. They should be considered temporary, and replaced with more complete, properly formatted citations as soon as possible. Embedded links should never be used to place external links in the content of an article, like this: "Apple Inc. announced their latest product ...".   === Convenience links ===  A convenience link is a link to a copy of your source on a web page provided by someone other than the original publisher or author. For example, a copy of a newspaper article no longer available on the newspaper's website may be hosted elsewhere. When offering convenience links, it is important to be reasonably certain that the convenience copy is a true copy of the original, without any changes or inappropriate commentary, and that it does not infringe the original publisher's copyright. Accuracy can be assumed when the hosting website appears reliable. For academic sources, the convenience link is typically a reprint provided by an open-access repository, such as the author's university's library or institutional repository. Such green open access links are generally preferable to paywalled or otherwise commercial and unfree sources. Where several sites host a copy of the material, the site selected as the convenience link should be the one whose general content appears most in line with Wikipedia:Neutral point of view and Wikipedia:Verifiability.   === Indicating availability ===  If your source is not available online, it should be available in reputable libraries, archives, or collections. If a citation without an external link is challenged as unavailable, any of the following is sufficient to show the material to be reasonably available (though not necessarily reliable): providing an ISBN or OCLC number; linking to an established Wikipedia article about the source (the work, its author, or its publisher); or directly quoting the material on the talk page, briefly and in context.   === Links to sources ===  For a source available in hardcopy, microform, and/or online, omit, in most cases, which one you read. While it is useful to cite author, title, edition (1st, 2nd, etc.), and similar information, it generally is not important to cite a database such as ProQuest, EBSCOhost, or JSTOR (see the list of academic databases and search engines) or to link to such a database requiring a subscription or a third party's login. The basic bibliographic information you provide should be enough to search for the source in any of these databases that have the source. Don't add a URL that has a part of a password embedded in the URL. However, you may provide the DOI, ISBN, or another uniform identifier, if available. If the publisher offers a link to the source or its abstract that does not require a payment or a third party's login for access, you may provide the URL for that link. If the source only exists online, give the link even if access is restricted (see WP:PAYWALL).   === Preventing and repairing dead links ===  To help prevent dead links, persistent identifiers are available for some sources. Some journal articles have a digital object identifier (DOI); some online newspapers and blogs, and also Wikipedia, have permalinks that are stable. When permanent links aren't available, consider making an archived copy of the cited document when writing the article; on-demand web archiving services such as the Wayback Machine (https://web.archive.org/save) or archive.today (https://archive.today) are fairly easy to use (see pre-emptive archiving). Do not delete a citation merely because the URL is not working. Dead links should be repaired or replaced if possible. If you encounter a dead URL being used as a reliable source to support article content, follow these steps prior to deleting it:  Confirm status: First, check the link to confirm that it is dead and not temporarily down. Search the website to see whether it has been rearranged. The online service "Is it down right now?" can help to determine if a site is down, and any information known. Check for a changed URL on the same Web site: Pages are frequently moved to different locations on the same site as they become archive content rather than news. The site's error page may have a "Search" box; alternatively, in both the Google and DuckDuckGo search engines – among others – the keyterm "site:" can be used. For instance: site:en.wikipedia.org "New Zealand police vehicle markings and livery". Check for web archives: Many web archiving services exist (for a full list, see: Wikipedia:List of web archives on Wikipedia); link to their archive of the URL's content, if available. Examples: Internet Archive has billions of archived web pages. See Wikipedia:Using the Wayback Machine. archive.today See Wikipedia:Using archive.today The UK Government Web Archive (https://www.nationalarchives.gov.uk/webarchive/) preserves 1500 UK central government websites. The Mementos interface allows you to search multiple archiving services with a single request using the Memento protocol. Unfortunately, the Mementos web page interface removes any parameters which are passed with the URL. If the URL contains a "?" it is unlikely to work properly. When entering the URL into the Mementos interface manually, the most common change needed is to change "?" to "%3F". While making only this change will not be sufficient in all cases, it will work most of the time. The bookmarklet in the table below will properly encode URLs such that searches will work.If multiple archive dates are available, try to use one that is most likely to be the contents of the page seen by the editor who entered the reference on the |access-date=. If that parameter is not specified, a search of the article's revision history can be performed to determine when the link was added to the article. For most citation templates, archive locations are entered using the |archive-url=, |archive-date= and |url-status= parameters. The primary link is switched to the archive link when |url-status=dead. This retains the original link location for reference. If the web page now leads to a completely different website, set |url-status=usurped to hide the original website link in the citation. Note: Some archives currently operate with a delay of ~18 months before a link is made public. As a result, editors should wait ~24 months after the link is first tagged as dead before declaring that no web archive exists. Dead URLs to reliable sources should normally be tagged with {{dead link|date=March 2023}}, so that you can estimate how long the link has been dead. Bookmarklets to check common archive sites for archives of the current page: Archive.org javascript:void(window.open('https://web.archive.org/web/*/'+location.href)) archive.today / archive.is javascript:void(window.open('https://archive.today/'+location.href)) Mementos interface javascript:void(window.open('https://www.webarchive.org.uk/mementos/search/'+encodeURIComponent(location.href)+'?referrer='+encodeURIComponent(document.referrer)))Remove convenience links: If the material was published on paper (e.g., academic journal, newspaper article, magazine, book), then the dead URL is not necessary. Simply remove the dead URL, leaving the remainder of the reference intact. Find a replacement source: Search the web for quoted text, the article title, and parts of the URL. Consider contacting the website/person that originally published the reference and asking them to republish it. Ask other editors for help finding the reference somewhere else, including the user who added the reference. Find a different source that says essentially the same thing as the reference in question. Remove hopelessly-lost web-only sources: If the source material does not exist offline, and if there is no archived version of the web page (be sure to wait ~24 months), and if you cannot find another copy of the material, then the dead citation should be removed and the material it supports should be regarded as unverified if there is no other supporting citation. If it is material that is specifically required by policy to have an inline citation, then please consider tagging it with {{citation needed}}. It may be appropriate for you to move the citation to the talk page with an explanation, and notify the editor who added the now-dead link.  When using inline citations, it is important to maintain text–source integrity. The point of an inline citation is to allow readers and other editors to see which part of the material is supported by the citation; that point is lost if the citation is not clearly placed. The distance between material and its source is a matter of editorial judgment, but adding text without clearly placing its source may lead to allegations of original research, of violations of the sourcing policy, and even of plagiarism.   === Keeping citations close === Editors should exercise caution when rearranging or inserting material to ensure that text–source relationships are maintained. References need not be moved solely to maintain the chronological order of footnotes as they appear in the article, and should not be moved if doing so might break the text–source relationship. If a sentence or paragraph is footnoted with a source, adding new material that is not supported by the existing source to the sentence/paragraph, without a source for the new text, is highly misleading if placed to appear that the cited source supports it. When new text is inserted into a paragraph, make sure it is supported by the existing or a new source. For example, when editing text originally reading  The sun is pretty big.Notes  an edit that does not imply that the new material is supported by the same reference is  The sun is pretty big. The sun is also quite hot.Notes  Do not add other facts or assertions into a fully cited paragraph or sentence:  N The sun is pretty big, but the moon is not so big. The sun is also quite hot.Notes  Include a source to support the new information. There are several ways to write this, including:  Y The sun is pretty big, but the moon is not so big. The sun is also quite hot.Notes   === Bundling citations ===  Sometimes the article is more readable if multiple citations are bundled into a single footnote. For example, when there are multiple sources for a given sentence, and each source applies to the entire sentence, the sources can be placed at the end of the sentence, like this.[4][5][6][7] Or they can be bundled into one footnote at the end of the sentence or paragraph, like this.[4]Bundling is also useful if the sources each support a different portion of the preceding text, or if the sources all support the same text. Bundling has several advantages:  It helps readers and other editors see at a glance which source supports which point, maintaining text–source integrity; It avoids the visual clutter of multiple clickable footnotes inside a sentence or paragraph; It avoids the confusion of having multiple sources listed separately after sentences, with no indication of which source to check for each part of the text, such as this.[1][2][3][4] It makes it less likely that inline citations will be moved inadvertently when text is re-arranged, because the footnote states clearly which source supports which point.To concatenate multiple citations for the same content, semicolons (or another character appropriate to the article's style) can be used. Alternatively, use one of the templates listed at the disambiguation page Template:Multiple references.  The sun is pretty big, bright and hot.Notes  For multiple citations in a single footnote, each in reference to specific statements, there are several layouts available, as illustrated below. Within a given article only a single layout should be used.  The sun is pretty big, but the moon is not so big. The sun is also quite hot.Notes  However, using line breaks to separate list items breaches WP:Accessibility § Nobreaks: "Do not separate list items with line breaks (<br>)." {{Unbulleted list citebundle}} was made specifically for this purpose; also available is {{unbulleted list}}.  In-text attribution is the attribution inside a sentence of material to its source, in addition to an inline citation after the sentence. In-text attribution should be used with direct speech (a source's words between quotation marks or as a block quotation); indirect speech (a source's words modified without quotation marks); and close paraphrasing. It can also be used when loosely summarizing a source's position in your own words, and it should always be used for biased statements of opinion. It avoids inadvertent plagiarism and helps the reader see where a position is coming from. An inline citation should follow the attribution, usually at the end of the sentence or paragraph in question. For example:  N To reach fair decisions, parties must consider matters as if behind a veil of ignorance.[2]  Y John Rawls argues that, to reach fair decisions, parties must consider matters as if behind a veil of ignorance.[2]  Y John Rawls argues that, to reach fair decisions, parties must consider matters as if "situated behind a veil of ignorance".[2]  When using in-text attribution, make sure it doesn't lead to an inadvertent neutrality violation. For example, the following implies parity between the sources, without making clear that the position of Darwin is the majority view:  N Charles Darwin says that human beings evolved through natural selection, but John Smith writes that we arrived here in pods from Mars. Y Humans evolved through natural selection, as first explained in Charles Darwin's The Descent of Man, and Selection in Relation to Sex. Neutrality issues apart, there are other ways in-text attribution can mislead. The sentence below suggests The New York Times has alone made this important discovery:  N According to The New York Times, the sun will set in the west this evening. Y The sun sets in the west each evening. It is preferable not to clutter articles with information best left to the references. Interested readers can click on the ref to find out the publishing journal:  N In an article published in The Lancet in 2012, researchers announced the discovery of the new tissue type.[3]  Y The discovery of the new tissue type was first published by researchers in 2012.[3]  Simple facts such as this can have inline citations to reliable sources as an aid to the reader, but normally the text itself is best left as a plain statement without in-text attribution:  Y By mass, oxygen is the third most abundant element in the universe after hydrogen and helium.[4]   If an article has no references at all, then:  If the entire article is "Patent Nonsense", tag it for speedy deletion using criterion G1. If the article is a biography of a living person, it can be tagged with {{subst:prod blp}} to propose deletion. If it's a biography of a living person and is an attack page, then it should be tagged for speedy deletion using criterion G10, which will blank the page. If the article doesn't fit into the above two categories, then consider finding references yourself, or commenting on the article talk page or the talk page of the article creator. You may also tag the article with the {{unreferenced}} template and consider nominating it for deletion.For individual claims in an article not supported by a reference:  If the article is a biography of a living person, then any contentious material must be removed immediately: see Biographies of living persons. If the material lacking reference is seriously inappropriate, it may need to be hidden from general view, in which case request admin assistance. If the material added appears to be false or an expression of opinion, remove it and inform the editor who added the unsourced material. The {{uw-unsourced1}} template may be placed on their talk page. In any other case consider finding references yourself, or commenting on the article talk page or the talk page of the editor who added the unsourced material. You may place a {{citation needed}} or {{dubious}} tag against the added text.  Citation templates can be used to format citations in a consistent way. The use of citation templates is neither encouraged nor discouraged: an article should not be switched between templated and non-templated citations without good reason and consensus – see "Variation in citation methods", above. If citation templates are used in an article, the parameters should be accurate. It is inappropriate to set parameters to false values to cause the template to render as if it were written in some style other than the style normally produced by the template (e.g., MLA style).   === Metadata === Citations may be accompanied by metadata, though it is not mandatory. Most citation templates on Wikipedia use the COinS standard. Metadata such as this allow browser plugins and other automated software to make citation data accessible to the user, for instance by providing links to their library's online copies of the cited works. In articles that format citations manually, metadata may be added manually in a span, according to the COinS specification.   === Citation generation tools ===  the Wikipedia Visual Editor now helps users format, insert and edit sources by simply providing a DOI, URL, ISBN etc. User:Ark25/RefScript, a JavaScript bookmarklet – creates references in one click, works for many newspapers User:V111P/js/WebRef, a script or bookmarklet automating the filling of the {{cite web}} template. You use the script on the page you want to cite. User:Badgettrg, Biomedical citation maker. uses Pubmed ID (PMID) or DOI or PMCID or NCT. Adds links to ACP Journal Club and Evidence-Based Medicine comments if present. WP:ReFill – adds titles to bare url references and other cleanup Template:Ref info, which can aid evaluating what kind of citation style was used to write the article Based on Citoid: Cite templates in Visual Editor User:Salix alba/Citoid a client for the mw:citoid server which generates Citation Style 1 templates from urls. RefTag: Reftag for DOI Reftag for New York Times Wikipedia DOI and Google Books Citation Maker Hosted on tools.wmflabs.org: Wikipedia:refToolbar 2.0, used in the Source Editor Citation bot Yadkard: A web-based tool for generating shortened footnotes and citation using Google Books URLs, DOI or ISBN. Also supports some news websites. Wikipedia template filling – generates Vancouver style citations from PMIDs (PubMed IDs).   === Duplicates finders === Finding duplicates by examining reference lists is difficult. There are some tools that can help:  AutoWikiBrowser (AWB) will identify and (usually) correct exact duplicates between <ref>...</ref> tags. See the documentation. URL Extractor For Web Pages and Text can identify Web citations with the exact same URL but otherwise possibly different. Occasionally references to the same Web page might be followed by different non-significant tracking parameters (?utm ..., #ixzz...), and will not be listed as duplicates. Step 1: enter the URL of the Wikipedia article and click "Load", Step 2: tick "Only Display duplicate URL addresses" (which unticks "Remove duplicate addresses") Optional: Tick the radio button "Do not show", tick the box at the beginning of its line, and enter into the box web.archive.org,wikipedia,wikimedia,wikiquote,wikidata Step 3: Click Extract. Then the duplicates will be listed, and must be manually merged. There will often be false positives; web.archive.org URLs, in particular, are a nuisance as they contain the original URLs, which shows as duplicates. The optional part of Step 2 eliminates the archive URLs, but unfortunately the list of duplicates includes the archived pages. The wiki* URLs are less of a problem as they can just be ignored.   === Programming tools ===  Wikicite is a free program that helps editors to create citations for their Wikipedia contributions using citation templates. It is written in Visual Basic .NET, making it suitable only for users with the .NET Framework installed on Windows, or, for other platforms, the Mono alternative framework. Wikicite and its source code is freely available; see the developer's page for further details. User:Richiez has tools to automatically handle citations for a whole article at a time. Converts occurrences of {{pmid XXXX}} or {{isbn XXXX}} to properly formatted footnote or Harvard-style references. Written in Ruby and requires a working installation with basic libraries. pubmed2wikipedia.xsl an XSL stylesheet transforming the XML output of PubMed to Wikipedia refs.   === Reference management software === Reference management software can output formatted citations in several styles, including BibTeX, RIS, or Wikipedia citation template styles.  Comparison of reference management software – side-by-side comparison of various reference management software Wikipedia:Citing sources with Zotero – essay on using Zotero to quickly add citations to articles. Zotero (by Roy Rosenzweig Center for History and New Media; license: Affero GPL) is open-source software with local reference database which can be synchronized between several computers over the online database (up to 300 MB without payment). EndNote (by Thomson Reuters; license: proprietary) Mendeley (by Elsevier; license: proprietary) Paperpile (by Paperpile, LLC; license: proprietary) Papers (by Springer; license: proprietary) How to cite  Wikipedia:References dos and don'ts – a concise summary of some of the most important guidance on this page Help:Referencing for beginners – a simple practical guide to getting started Help:How to mine a source – how-to guide on getting maximum information from cited material Wikipedia:Verification methods – listing examples of the most common ways that citations are used in Wikipedia articles Wikipedia:Improving referencing efforts – essay on why references are important Wikipedia:Citation templates – a full listing of various styles for citing all sorts of materials Wikipedia:Citing sources/Example edits for different methods – showing comparative edit mode representations for different citation methods and techniques Wikipedia:Citing sources/Further considerations – additional considerations for citing sources Wikipedia:Inline citation – more information on inline citations Wikipedia:Nesting footnotes – how-to guide on "nesting" footnotes Wikipedia:Manual of Style/Layout § Further reading – for information about the "Further reading" section Wikipedia:External links – for information about the "External links" section Wikipedia:Plagiarism § Public-domain sources – guideline covering the inclusion of material in the public domain Wikipedia:Scientific citation guidelines – guidelines for dealing with scientific and mathematical articles Wikipedia:WikiProject Resource Exchange/Shared Resources – project guide on finding resources MediaWiki:Extension:Cite – details of the software which support the <ref> parser hooksCitation problems  Template:Irrelevant citation – inline template to note source simply is not relevant to the material Template:More citations needed – template to add to article (or section) where citations are insufficient Template:Text-source – template to add to article (or section) where text–source integrity is questioned Wikipedia:Citation needed – explanation of template to tag statements that need a citation Wikipedia:Citation overkill – why too many citations on one fact can be a bad thing Wikipedia:Copyright problems – in case of text that has been copied verbatim inappropriately Wikipedia:Link rot – guide to preventing link rot Wikipedia:More seasoning doesn't mean more flavor – an essay about how less detail doesn't always mean less info Wikipedia:You don't need to cite that the sky is blue – an essay advising: do not cite already obvious information Wikipedia:You do need to cite that the sky is blue – an essay advising: just because something appears obvious to you does not mean it is obvious to everyone Wikipedia:Video links – an essay discussing the use of citations linking to YouTube and other user-submitted video sites Wikipedia:WikiProject Citation cleanup – a group of people devoted to cleaning up citations Wikipedia:Reference database – essay/proposalChanging citation style formats  WP:CITEVAR  "Online Style Guide". New Oxford Style Manual. Oxford, UK: Oxford University Press. 2016. ISBN 978-0198767251. The Chicago Manual of Style (17th ed.). Chicago: University of Chicago Press. 2017. ISBN 978-0226287058. "Academic Writing: Citing Sources". Writers Workshop. University of Illinois. "Citation Style Guides & Management Tools". Library Guides. LIU Post. "Citing: Help & how-to". Concordia University Library. "Citation Help". Subject Guides. University of Iowa. "Guide to Citation Style Guides". Journalism Resources. University of Iowa. "Library: Citing Sources & Citation Generators". Capital Community College. "Research and Citation Resources". Online Writing Lab. Purdue University. "The Writer's Handbook: Documentation". Writing Center. University of Wisconsin–Madison. "ACS Style Guide". Research Guides. University of Wisconsin–Madison. "Samples of Formatted References for Authors of Journal Articles". MEDLINE and PubMed: The Resources Guide. United States National Library of Medicine. 26 April 2018.  "reFill". Toolforge. WP:ReFill. – tool that expands bare references semi-automatically Wikipedia editing basics: Citing sources (part 1) (YouTube). Wikimedia Foundation. Wikipedia editing basics: Citing sources (part 2) (YouTube). Wikimedia Foundation.