Wikipedia:WikiProject Check Wikipedia/List of errors

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Data for the list is compiled from the following locations: WPCleaner • AutoWikiBrowser • Auto-Formatter.

  Fixes all cases     Warns of an error and fixes some cases     Warns of an error
Quick link templates
Target use example
this list {{CW|##}} {{CW|50}} → CW Error #50
the CheckWiki report {{Checkwiki|##}} {{Checkwiki|50}} → CW Error #50
# Priority Cosmetic Error WPC AWB AF Type Reason
01
(dump) 		Low Yes Template contains useless word "template:" checkY checkY checkY Syntax error Article contains a template that includes the redundant prefix "template:" (eg. {{template:reflist}}). Removing it is usually useful when copying page in another Wikipedia.
02
(dump) 		High Sometimes <br>, <center> or <small> tag with incorrect syntax. Cases of <span /> and <div />. checkY checkY checkY Syntax error A <br> or <br /> tag (note the slash) are the only standard formats. See the HTML standard for <br> or <small>.
Mediawiki's Tidy tool will be replaced which may cause many now valid tags, such as </br> and <center />, to no longer work.
03
(dump) 		High No Reference list missing / disambiguation page with disallowed <ref> checkY checkY Display problem The article contains one or more <ref> tags, but is missing a {{Reflist}} or <references /> tag. Or a disambiguation page contains a disallowed <ref> tag, see WP:DABREF.
04
(dump) 		Mid No HTML text style element <a> checkY Display problems The article contains one or more <a> tags. <a> tags will not show up in the rendered article and should use normal wikilink code for external links.
05
(dump) 		High No Comment tag with no correct end Display problem Missing closing comment tag. <!-- -->
06 Low No DEFAULTSORT with special characters checkY checkY checkY Syntax error Don't use special lettering in DEFAULTSORT
07
(dump) 		Mid No Headlines all start with three "=" checkY checkY Accessibility First headline starts with "=== XY ===". It should be "== XY ==" header. This causes organisational and accessibility problems.
08
(dump) 		High No Headline should end with "=" checkY checkY Display problem Headline should end with "=".
09
(dump) 		Low Yes Multiple categories on one line checkY checkY checkY Against convention Two or more categories on one line.
10 High No Square brackets with no correct end checkY checkY Display problem Found a "[[" brackets with no corresponding "]]" brackets.
11 Off Yes HTML named entities checkY checkY Source readability HTML code found where a Unicode character could be used. For example, &auml; used instead of ä. It is difficult to comprehend for beginners.
12 Low ? HTML list elements Source readability Detection of <ol>, <ul>...</ul> or <li> tags. Sometimes it is necessary to have these tags, especially in infoboxes.
13
(dump) 		High No <math> tag without correct match Display problem Missing </math> or <math> tag.
14
(dump) 		High No <source> tag without correct match Display problem Missing </source> or <source> tag.
15
(dump) 		High No <code> tag without correct match Display problem Missing </code> or <code> tag.
16
(dump) 		Low Yes[a] Unicode control characters checkY checkY Incident detection Detection of Unicode controls such as 0+FEFF, 0+200E, 0+200B and PUA characters.
17
(dump) 		Low Yes[a] Category duplication checkY checkY Incident detection Unnecessary duplicate categories found.
18 Off Yes Category's first letter is small checkY checkY checkY Against convention Against convention. If turned on again, check if CamelCase cases (e.g. Category:iPhone) have consensus to be changed to

(e.g. Category:IPhone).

19
(dump) 		High No Headlines start with one "=" checkY Accessibility A heading section starts with just one "=". This causes organisational and accessibility problems
20
(dump) 		Low Yes Symbol for dead checkY checkY checkY Source readability The article had a &dagger; and not †
21 Off No Category: in English checkY checkY Incident detection [[Category: ]] found when the native language should be used
22 Off Yes Category with space checkY checkY checkY Against convention Category contains an unnecessary space, for example: [[ Category:ABC]] or [[Category : ABC]].
23
(dump) 		High No <nowiki> without correct match Display problem Missing </nowiki> or <nowiki> tag.
24
(dump) 		High No <pre> without correct match Display problem Missing </pre> or <pre> tag.
25
(dump) 		Mid No Headline hierarchy checkY checkY Accessibility After a section headline "==", there should not be a headline of "====". This causes organisational and accessibility problems.
26
(dump) 		Low Yes HTML text style element <b> (bold) checkY checkY Accessibility
Source readability 		Found a <b> tag. Should use wiki markup of '''. See WP:Deviations
27 Off Yes Unicode syntax checkY checkY checkY Source readability &#169; gives very little clue as to what this is supposed to be. Use &copy; or the symbol directly ©. Some entries, like the [ ] brackets should remain in unicode, or converted to {{!(}} and {{!)}} when used in external links.
28
(dump) 		High No Table with no correct end Display problem An opening table has "{|" tag, but no corresponding closing "|}" tag.
29
(dump) 		High No <gallery> without correct match Display problem Missing </gallery> or <gallery> tag.
30 Off No Image without alternate description Accessibility
31 Low ? HTML table element Source readability A <table>, <tr> or <td> tag was found. Should use wiki markup instead.
32 High No Double pipe in a link checkY checkY Display problem Article contains a wikilink like [[text|text2|text3]] (displays as text2|text3), [[text||text3]] or [[text|text2||]]. or a broken wikilink inside a table.
33 Off ? HTML text style element <u> (underline) checkY Against convention
34 High No Template programming element checkY Syntax error A template programming element, such as {{{1}}}, #if or #switch, was found. They are usually not needed or a regular template can be substituted instead.
35 Off No Image gallery without description checkY Accessibility
36 Low No Redirect with incorrect syntax checkY checkY Display problem Redirect will not work
37 Low No DEFAULTSORT missing for titles with special letters checkY checkY Display problem Don't use special lettering for sorting. DEFAULTSORT should be set without the special lettering.
38
(dump) 		Low Yes HTML text style element <i> (italics) checkY checkY Accessibility
Source readability 		Found a <i> tag. Should use wiki markup of ''. See WP:Deviations
39 Low No HTML text style element <p> checkY Accessibility Found a <p> tag. Usually should use wiki markup's blank line. Some tags, such as <ref> must use <p> due to a wikimedia bug.
40 Low ? HTML text style element <font> checkY checkY Against convention Found a <font> tag. This tag isn't used in HTML5
41 Off ? HTML text style element <big> Against convention Found a <big> tag. This tag isn't used in HTML5
42
(dump) 		Low ? HTML text style element <strike> checkY checkY checkY Accessibility Found a <strike> tag. This tag isn't used in HTML5. Use <s> instead. However, strikes shouldn't be used at all for accessibility reasons, so removing the strike is usually the best option.
43 High No Template with no correct end checkY checkY Display problem Found a "{{" brackets with no corresponding "}}" brackets.
44 Low No Headlines with bold checkY checkY checkY Against convention A headline is all or partially bold. This should rarely be used and may or not be bold depending on the browser used.
45 Low No Interwiki duplication checkY checkY Display problem Duplicate entry. Now that interwiki links have been moved to wikidata, this error is possibly due to wikilinks that ought to be rendered that omits the leading : in [[:pt:Jorge de Mascarenhas]]. Should often be converted to internal redlinks per WP:BUILD/WP:REDLINK.
46 High No Square brackets without correct beginning checkY checkY Display problem Found a "]]" brackets with no corresponding "[[" brackets.
47 High No Template without correct beginning Display problem Found a "}}" brackets with no corresponding "{{" brackets.
48
(dump) 		Low No Title linked in text checkY checkY Display problem A wikilink of the article's title was found. This creates an unnecessary circular wikilink per MOS:OVERLINK/WP:SELFREDIRECT and inappropriately bolds the linked word.
49 High No Headline with HTML checkY Accessibility
Source readability 		Found a headline created with HTML tags <h1>, <h2>, etc. per MOS:DEVIATIONS and MOS:HEAD.
50 Off Yes en dash or em dash checkY checkY
51 Mid No Interwiki before last headline checkY checkY Syntax error With interwikis no long used, this usually means a syntax problem with a interlanguage link, ie [[de:foo]] instead of [[:de:foo]]
52 Low Yes Category before last headline checkY checkY Against convention Categories should be placed in the last section. If a link is intentional, used [[:Category:Foobar]]
53 Mid No Interwiki before last category checkY checkY Syntax error With interwikis no long used, this usually means a syntax problem with a interlanguage link, ie [[de:foo]] instead of [[:de:foo]]
54
(dump) 		Low No Break in list checkY checkY checkY Accessibility WP:LISTGAP
55
(dump) 		Low No Double <small> tags checkY checkY Accessibility Causes the text to be smaller than 85%. This goes against accessibility guidelines.
56 Off No Arrow as ASCII art checkY The article had an arrow like "<--" or "-->" or "<==" or "==>". Write better this arrow with the Unicode "←" or "→" or "⇐" or "⇒".
57 Low No Headlines end with a colon checkY checkY checkY Against convention Remove the :
58 Mid No Headline all CAPS checkY Against convention Headlines should normally use sentence case, unless referring to titles of works and all-caps acronyms.
59 Low Yes Template value ends with a <br> checkY checkY Syntax error May cause whitespace errors (unconfirmed as of 2023)
60 High No Template parameter with a problem Syntax error Usually means a broken wikilink inside a template. Can also mean the '=' sign is missing and replaced with another character.
61 Low No Reference before punctuation checkY checkY checkY Display problem <ref> comes after not before various punctuation marks (.,?:;!); see WP:REFPUNC
62 High No URL without http:// checkY Syntax error A URL was found that contained no http://. Example: [en.wikipedia.org Wikipedia]
63 Low No <small> in a <ref>, <sub> or <sup> checkY checkY checkY Accessibility <ref> and <sub> tags already create smaller text. Adding a <small> would cause the text to be smaller than 85%. This goes against accessibility guidelines.
64
(dump) 		Low Yes Link equal to linktext checkY checkY checkY Syntax error Finds cases of [[Foo|Foo]]. A Visual Editor bug causes wikilinks with italics or bold to be done incorrectly, usually some text outside the wikilink will also be bold or italized. Moreover, WP:NOPIPEDLINK.
65 Low Yes Image description ends with <br> checkY checkY Syntax error Clutter/Does nothing
66 Low No Image description with full <small> checkY checkY Accessibility Image description text is already smaller. Adding a <small> would cause the text to be smaller than 85%. This goes against accessibility guidelines.
67 Off No Reference after punctuation (see 61 instead) checkY
68 Off No Link to other language checkY
69
(dump) 		Mid No ISBN with incorrect syntax checkY checkY checkY Incorrect content Per WP:ISBN, the correct format is ISBN 978-2345-78383-1. Also finds ISBNs inside external links as Wikimagick doesn't work and ISBN template can cause problems.
70
(dump) 		Mid No ISBN with wrong length Incorrect content ISBNs should have a length of 10 or 13 characters
71
(dump) 		Mid No ISBN with wrong position of X Incorrect content X is only allowed in the last position of the ISBN
72
(dump) 		Mid No ISBN-10 with wrong checksum Incorrect content ISBN checksum is wrong, verify the ISBN
73
(dump) 		Mid No ISBN-13 with wrong checksum Incorrect content ISBN checksum is wrong, verify the ISBN
74 High No Link with no target checkY checkY Against convention
Incorrect content 		[[|foobar]] links to foobar. The pipe is either unneeded, someone forgot to give a target, or someone vandalized the article.
75 Off ? Indented list checkY
76 Low ? Link with encoded space checkY checkY checkY Source readability Found a URI encoded space, ie %20, inside a wikilink. This usually indicates a badly constructed external link.
77 Off No Image description with partial <small> checkY
78 Low No Reference list duplication checkY Display problem Found two or more {{reflist}} or <references /> tags
79 Off No External link without description checkY
80 High No External link with a line break checkY checkY Display problem Found a newline character inside an external link or a missing closing bracket. A newline character causes the link not to work.
81 Low ? Reference duplication checkY checkY Saves wikitext, and makes it easier to maintain the article, as you will only need to change one entry to update multiple instances of the same reference
82 Off ? Link to other wikiproject
83
(dump) 		Mid No Headlines start with three "=" and later with two "=" checkY Accessibility Organisational and accessibility problems.
84 Off No Section without content checkY checkY
85 Low ? Tags without content checkY checkY Source readability An empty <ref></ref> or <span></span> serves no purpose. This can be confusing to editors, and lead to issues if someone interacts with the empty tags by mistake.
86 High No External link with two brackets checkY checkY checkY Display problem Found an external links surround by double brackets.
Example: [[http://www.wikipedia.org Wikipedia]]
# Priority Cosmetic Error WPC AWB AF Type Reason
87 Off No HTML named entities without semicolon checkY checkY Display problem
88 Low Yes DEFAULTSORT with a blank at first position checkY checkY checkY Against convention The space in {{DEFAULTSORT: DuBois, Lewis}} is useless and ignored by MediaWiki.
89 Low No DEFAULTSORT with no space after the comma checkY Syntax error The script found a DEFAULTSORT without a space after the comma {{DEFAULTSORT:DuBois,Lewis}}. The causes the article to be sorted as the first DuBois article.
90 Mid No Internal link written as an external link checkY checkY Syntax error The script found an external link that should be replaced with a wikilink. An example would be on enwiki [http://en.wikipedia.orgview_html.php?sq=&lang=&q=Larry_Wall Larry Wall] should be written as [[Larry Wall]].
91 Mid No Interwiki link written as an external link checkY checkY Syntax error The script found an external link that should be replaced with an interwiki link. An example would be on enwiki [http://fr.wikipedia.orgview_html.php?sq=&lang=&q=Larry_Wall Larry Wall] should be written as [[:fr:Larry Wall]].
92
(dump) 		Off No Headline double checkY Accessibility This causes navigation and accessibility issues
93 Mid No External link with double http:// checkY checkY Syntax error The script found an external link that had double http://. An example would be [http://http://www.google.com]
94 Mid No Reference tags with no correct match checkY Display problem A <ref> or </ref> tag was found without the corresponding beginning or ending tag.
95 Low No Editor's signature or link to user or draft space Syntax error See Wikipedia:UPYES and WP:SIGNHERE
96 Mid No Table of Contents after first headline Accessibility TOC should be placed at the end of the lead section of the text, before the first section heading. Users of screen readers do not expect any text between the TOC and the first heading. See WP:TOC.
97 Mid No TOC has material after it and before the first headline Accessibility Screen readers don't process material that comes between the Table of Contents and first headline. See WP:TOC.
98
(dump) 		High No <sub> with no correct end checkY checkY Display problem Missing </sub> tag. Can cause display problems in Visual Editor and mw:Html5Depurate
99
(dump) 		High No <sup> with no correct end checkY checkY Display problem Missing </sup> tag. Can cause display problems in Visual Editor and mw:Html5Depurate
100
(dump) 		Low ? List tag with no correct match Source readability List tag (<ol>, <ul> or <li>) with no correct match.
101
(dump) 		Low No Ordinal number found inside <sup> tags checkY Against convention Ordinal numbers should be in regular text, not inside <sup> tags See MOS:ORDINAL.
102
(dump) 		Mid No PMID with incorrect syntax checkY checkY checkY Incorrect content Per WP:PMID, the syntax should be PMID 4957203 Also checks if PMID is inside an external link as Magiclinks and {{PMID}} template won't work.
103
(dump) 		Mid No Pipe Template inside a wikilink checkY Syntax error The magic word {{!}} shouldn't be used inside a wikilink. | should be used instead.
104
(dump) 		Mid No Unbalanced quotes in ref name checkY checkY checkY Syntax error The script found unbalanced quotes in a reference tag. For example <ref name="ref 1>
105
(dump) 		High No Heading should begin with "=" Display problem A heading should begin with a "=".
106
(dump) 		Mid No ISSN with incorrect syntax checkY checkY checkY Display problem The script found a problem with ISSN syntax. A normal ISSN looks like ISSN 3895-2372 or 3957-957X. There must be a - between the numbers (don't use dashes). Best if {{ISSN}} template is added. Also finds cases where the ISSN is inside an external linkss
107
(dump) 		Mid No ISSN with wrong length Incorrect content The script checked the ISSN and found it not containing 8 characters. ISSN should have 8 characters.
108
(dump) 		Mid No ISSN with wrong checksum Incorrect content The script checked the ISSN and found a problem with the checksum in the ISSN. Also see Category:Articles with invalid ISSNs.
109
(dump) 		High No Include tag error Display problem The script found a problem with opening or closing tags for <includeonly>, <onlyinclude> or <noinclude> tags. This can cause transclusion problems.
110 Off No Include tag found Display problem The script found a <includeonly>, <onlyinclude> or <noinclude> tags.
111
(dump) 		Off No Ref after last reference list Display problem There are <ref> tags, after the {{reflist}} or <references> tags.
112 Low ? Bad or deprecated css attributes Display problem Bad CSS should be fixed. Deprecated values should be updated for modern rendering.
113 Low No Newline inside a wikilink Display problem Found a newline character inside a wikilink. A newline character causes the wikilink not to work.
Note: errors starting at #500 are not detected by CheckWiki, but only by WPC.
501 Bot No Spelling and typography checkY Proposals for fixing spelling and typography based on suggestions.
502 Off Yes Template namespace in template usage checkY checkY Replaced by CW Error #1
503 Off No Internal link in title
504
(dump) 		Off No Reference in title
505 Off No Image without alternative description
506 Off No Reference with a numeric name
507 Off No Gallery without caption
508 Off No Missing template
509 Off Yes Internal link could be compacted checkY checkY
510 Off No Non working pipe trick
511 Off No Internal link written as external link checkY Replaced by CW Error #90
512 Off No Interwiki link written as external link checkY Replaced by CW Error #91
513
(dump) 		Off No Internal link inside external link An external links contains an internal link, see Special:LintErrors/wikilink-in-extlink
514 Off No Missing named reference
515 Off ? Title linked in text through redirect link
516 Off Yes <br /> tags in main namespace
517 Off ? strike tags checkY Replaced by CW Error #42
518 Bot ? nowiki tags in main namespace nowiki tags are often not needed in main namespace
519 Off ? a tags in main namespace Replaced by CW Error #4
520 Off ? Weird characters (pawns, snowmen) in main namespace
521 Bot ? Date format in templates
522 Off ? Empty title An empty title (like == <nowiki /> ==) has been detected.
523 Off ? Duplicate image
524 Low ? Duplicate arguments in template calls checkY See Category:Pages using duplicate arguments in template calls
525 Off ? Span tag
526
(dump) 		Off ? Incorrect date link Incorrect link to a date, like [[1985|2005]]
527 Low ? Reference with different content Reference tags have the same name but different content, see Category:Pages with duplicate reference names
528 Off ? PMID magic link PMID magic links will be removed from MW, see Category:Pages using PMID magic links
529 Off ? ISBN magic link ISBN magic links will be removed from MW, see Category:Pages using ISBN magic links
530 Off ? RFC magic link RFC magic links will be removed from MW, see Category:Pages using RFC magic links
531 Off ? Reference inside reference Reference tags have been found inside an other reference tag
532 Bot ? Missing end tag checkY An opening tag has no matching end tag, see Special:LintErrors/missing-end-tag.
533 Bot ? Multi colon escape checkY checkY A link has been created with a multi colon escape like Test, see Special:LintErrors/multi-colon-escape.
534 Bot ? Bogus image options checkY An image has been created with a bogus option, see Special:LintErrors/bogus-image-options.
535 Bot ? Tidy bug affecting font tags wrapping links checkY Tidy bug affecting font tags wrapping links, see Special:LintErrors/tidy-font-bug.
536 Bot ? Tidy whitespace bug checkY Tidy whitespace bug, see Special:LintErrors/tidy-whitespace-bug.
537 Bot ? Unclosed quotes in heading checkY Unclosed quotes in heading, see Special:LintErrors/unclosed-quotes-in-heading.
538 Bot Yes Whitespace characters after heading checkY checkY Extra whitespace characters are present after a heading (like == Title == ).
539 Bot ? Misnested tags checkY Misnested tags, see Special:LintErrors/misnested-tag.
540 Bot ? Missing end bold/italic checkY Missing end bold/italic, see Special:LintErrors/missing-end-tag.
541 Off ? Obsolete tag checkY checkY Obsolete tag, see Special:LintErrors/obsolete-tag.
542 Bot ? Empty ref tag checkY <ref> tag without any content like <ref></ref>.
543
(dump) 		Bot ? Pipe in external link checkY checkY like [https://test.org/toto.html| toto].
544 Off ? Missing end template in a pair A template designed to be paired with another template is alone, like {{col-begin}} without {{col-end}}.
545 Low ? Template with deprecated parameter A template parameter is obsolete, like writing_credits in {{Soundtrack}}.
546 Off ? Article without categories An article doesn't have any category, except for optional maintenance categories.
547
(dump) 		Off ? Empty list item A list item is empty, like *.
548
(dump) 		Off ? Punctuation in link A link ends with a punctuation, which should usually be better placed after the link (like [[Test|test,]]).
549
(dump) 		Off ? Split link A link is split in several parts (like [[Test|te]][[Test|st]]).
550
(dump) 		Off ? Link without text A link doesn't have any text, so it's not displayed (like [[Test|<nowiki/>]]).
551
(dump) 		Off ? Empty line A line is only composed of non displayed elements (like ''<nowiki/>'').
552
(dump) 		Off ? Template ending with }}} A templates end with }}} instead of }}.
553
(dump) 		Off ? <nowiki /> after internal link An internal link is followed by a <nowiki /> tag.
554
(dump) 		Off ? <nowiki /> in <gallery>...</gallery> A <nowiki /> tag is inside a <gallery>...</gallery> tag.
555
(dump) 		Off ? <nowiki /> in the text A <nowiki /> tag is in the text.
556
(dump) 		Off ? External link External link in the text of the article.
557
(dump) 		Off ? Missing whitespace before a link A link is just after the preceding text.
558
(dump) 		Off ? Duplicated reference A reference is used several times for the same text.
559 Off ? Separator between <ref /> tags Consecutive <ref /> tags are not properly separated.
560
(dump) 		Off ? Duplicated attribute A tag contains the same attribute several time.
561 Off ? Redirection with target text An internal link targets a redirection but display the name of the final target (like [[REDIRECT|TARGET]] with REDIRECT being a redirect to TARGET).
562
(dump) 		Off ? Consecutive <nowiki /> tags Several <nowiki /> tags are used one after another.
563 Off ? Unused parameters checkY A template has unused empty parameters.
564 Off ? Unknown parameters A template has unknown parameters.
565
(dump) 		Off ? <nowiki /> tag between bold/italic A <nowiki /> tag is used between bold/italic.
566 Off ? <abbr /> tag Abbreviation should use templates instead of <abbr /> tag.
# Priority Cosmetic Error WPC AWB AF Type Reason
  1. ^ a b Technically cosmetic, however this is either deemed too much of a bad practice, or prevents future issues deemed egregious enough to warrant a deviation from WP:COSMETICBOT.