This page documents a Wikidata policy. It is a widely accepted standard that all editors should normally follow. All changes made to it (except for minor edits such as fixing typos) should reflect consensus. When in doubt, discuss your idea on the project chat.
Note that the guidelines below are intentionally left a bit vague. In case of disagreement over the notability of an item, you can launch a request for deletion. The final decision is always up to the community.
Wikidata in its first phases has two main goals: to centralize interlanguage links across Wikimedia projects and to serve as a general knowledge base for the world at large. An item is acceptable if and only if it fulfills at least one of these two goals; that is, if it meets at least one of the three criteria below:
It contains at least one valid sitelink to a page on Wikipedia, Wikivoyage, Wikisource, Wikiquote, Wikinews, Wikibooks, Wikidata, Wikispecies, Wikiversity, or Wikimedia Commons.
To be valid, a link must not be a talk page, page in MediaWiki namespace, special page, file, translations page, page in User or Draft namespace, page used by LiquidThreads (i. e. page in Thread and Summary namespace), page used by Structured Discussions (i.e., page in Topic namespace), subpage of Portal namespace, or any page that is intended for TemplateStyles (i. e. suffix that contain ".css" and/or ".js"). Note that a single Wikimedia page cannot have more than one sitelink in Wikidata. It is permitted for a sitelink to point to a redirect (although the software intentionally makes this difficult), but such a link will not count towards establishing notability.
If a link is a template, the item must contain at least two such sitelinks, and any of them must not be one of /doc, /XML, /meta, /sandbox, /testcases or /TemplateData subpages. Items for non-subpages can be created with only one sitelink, but shouldn't be created in great numbers.
If a link is a subpage of a module, it must not be a /doc page.
Category items with a sitelink only to Wikimedia Commons are not permitted, unless either a) there is a corresponding main item which has a sitelink to a Commons gallery or b) the item is used in a Commons-related statement, such as category for pictures taken with camera (P2033).
On Wikisource, items for mainspace pages, Author pages, Translation pages, and Portal pages are valid, along with items for namespaces that exist on other Wikimedia sites (Category, Project...). Pages in the Index and Page namespaces are not considered valid. The status of subpages of mainspace pages (for example, individual chapters) is undetermined.
On Wikinews, pages in the Comments namespace are not considered valid.
On Wikidata, pages in namespace for structured data (currently includes items, properties, lexemes, EntitySchemas) are not allowed as target sitelink.
On Wiktionary, items for citation pages are not allowed. Main namespace is also excluded because interlanguage links are automatically provided by Cognate.
Status of pages in Meta-Wiki, MediaWiki.org, Wikimania and other supported special Wikimedia sites is undetermined. They should be discussed in a case-by-case basis.
It refers to an instance of a clearly identifiable conceptual or material entity. The entity must be notable, in the sense that it can be described using serious and publicly available references.
It fulfills a structural need, for example: it is needed to make statements made in other items more useful.
↑Sitelink to redirect should carry a sitelink badge that indicates the redirect status of the target page on the client wiki. Such a sitelink can be added to an Item if and only if a redirect badge is added in the same edit. If available, a template corresponding to Template:Wikidata redirect (Q16956589) should also be added to the redirect page, to show that the Wikidata sitelink is intentional, and not eg the unintended left-over effect of a Wikipedia article merge that should also have been reflected on Wikidata. Sitelinks to redirects should typically not be created unless (a) there is a substantial section about the subject on the target page of the redirect, reflecting all or most of the information in the Wikidata item; and (b) there is good reason not to merge the two corresponding Wikidata items.