A featured article exemplifies Wikipedia's very best work and is distinguished by professional standards of writing, presentation, and sourcing. In addition to meeting the policies regarding content for all Wikipedia articles, it has the following attributes.
It is:
well-written: its prose is engaging and of a professional standard;
comprehensive: it neglects no major facts or details and places the subject in context;
well-researched: it is a thorough and representative survey of the relevant literature; claims are verifiable against high-quality reliable sources and are supported by inline citations where appropriate;
stable: it is not subject to ongoing edit wars and its content does not change significantly from day to day, except in response to the featured article process; and
a lead: a concise lead section that summarizes the topic and prepares the reader for the detail in the subsequent sections;
appropriate structure: a substantial but not overwhelming system of hierarchical section headings; and
consistent citations: where required by criterion 1c, consistently formatted inline citations using footnotes—see citing sources for suggestions on formatting references. Citation templates are not required.
Length. It stays focused on the main topic without going into unnecessary detail and uses summary style where appropriate.
Professional, outstanding, and thorough; a definitive source for encyclopedic information.
No further content additions should be necessary unless new information becomes available; further improvements to the prose quality are often possible.
Prose. It features professional standards of writing.
Lead. It has an engaging lead that introduces the subject and defines the scope and inclusion criteria.
Comprehensiveness.
(a) It comprehensively covers the defined scope, providing at least all of the major items and, where practical, a complete set of items; where appropriate, it has annotations that provide useful and appropriate information about the items.
(c) In length and/or topic, it meets all of the requirements for stand-alone lists and includes at minimum eight items; does not violate the content-forking guideline, does not largely duplicate material from another article, and could not reasonably be included as part of a related article.
Structure. It is easy to navigate and includes, where helpful, section headings and table sort facilities.
Style. It complies with the Manual of Style and its supplementary pages.
(a) Visual appeal. It makes suitable use of text layout, formatting, tables, and colour; and a minimal proportion of items are redlinked.
Stability. It is not the subject of ongoing edit wars and its content does not change significantly from day to day, except in response to the featured list process.
Professional standard; it comprehensively covers the defined scope, usually providing a complete set of items, and has annotations that provide useful and appropriate information about those items.
No further content additions should be necessary unless new information becomes available; further improvements to the prose quality are often possible.
The article is well organized and essentially complete, having been examined by impartial reviewers from a WikiProject or elsewhere. Good article status is not a requirement for A-Class.
More detailed criteria
The article meets the A-Class criteria:
Provides a well-written, clear and complete description of the topic, as described in Wikipedia:Article development. It should be of a length suitable for the subject, appropriately structured, and be well referenced by a broad array of reliable sources. It should be well illustrated, with no copyright problems. Only minor style issues and other details need to be addressed before submission as a featured article candidate. See the A-Class assessment departments of some of the larger WikiProjects (e.g. WikiProject Military history).
Very useful to readers. A fairly complete treatment of the subject. A non-expert in the subject would typically find nothing wanting.
Expert knowledge may be needed to tweak the article, and style problems may need solving. WP:Peer review may help.
it contains a list of all references (sources of information), presented in accordance with the layout style guideline;
reliable sources are cited inline. All content that could reasonably be challenged, except for plot summaries and that which summarizes cited content elsewhere in the article, must be cited no later than the end of the paragraph (or line if the content is not in prose);
Useful to nearly all readers, with no obvious problems; approaching (though not necessarily equalling) the quality of a professional publication.
Some editing by subject and style experts is helpful; comparison with an existing featured article on a similar topic may highlight areas where content is weak or missing.
The article meets all of the B-Class criteria. It is mostly complete and does not have major problems, but requires some further work to reach good article standards.
The article reasonably covers the topic, and does not contain obvious omissions or inaccuracies. It contains a large proportion of the material necessary for an A-Class article, although some sections may need expansion, and some less important topics may be missing.
The article has a defined structure. Content should be organized into groups of related material, including a lead section and all the sections that can reasonably be included in an article of its kind.
The article is reasonably well-written. The prose contains no major grammatical errors and flows sensibly, but does not need to be of the standard of featured articles. The Manual of Style does not need to be followed rigorously.
The article contains supporting materials where appropriate. Illustrations are encouraged, though not required. Diagrams, an infobox etc. should be included where they are relevant and useful to the content.
Readers are not left wanting, although the content may not be complete enough to satisfy a serious student or researcher.
A few aspects of content and style need to be addressed. Expert knowledge may be needed. The inclusion of supporting materials should be considered if practical, and the article checked for general compliance with the Manual of Style and related style guidelines.
The article is substantial but is still missing important content or contains irrelevant material. The article should have some references to reliable sources, but may still have significant problems or require substantial cleanup.
More detailed criteria
The article cites more than one reliable source and is better developed in style, structure, and quality than Start-Class, but it fails one or more of the criteria for B-Class. It may have some gaps or missing elements, or need editing for clarity, balance, or flow.
Useful to a casual reader, but would not provide a complete picture for even a moderately detailed study.
Considerable editing is needed to close gaps in content and solve cleanup problems.
An article that is developing but still quite incomplete. It may or may not cite adequate reliable sources.
More detailed criteria
The article has a meaningful amount of good content, but it is still weak in many areas. The article has one or more of the following:
A useful picture or graphic
Multiple links that help explain or illustrate the topic
A subheading that fully treats an element of the topic
Multiple subheadings that indicate material that could be added to complete the article
Provides some meaningful content, but most readers will need more.
Providing references to reliable sources should come first; the article also needs substantial improvement in content and organisation. Improve the grammar, spelling, and writing style; decrease the use of jargon.
A very basic description of the topic. Meets none of the Start-Class criteria.
Provides very little meaningful content; may be little more than a dictionary definition. Readers probably see insufficiently developed features of the topic and may not see how the features of the topic are significant.
Any editing or additional material can be helpful. The provision of meaningful content should be a priority. The best solution for a Stub-class Article to step up to a Start-class Article is to add in referenced reasons of why the topic is significant.
Meets the criteria of a stand-alone list or set index article, which is an article that contains primarily a list, usually consisting of links to articles in a particular subject area.
There is no set format for a list, but its organization should be logical and useful to the reader.
Lists should be lists of live links to Wikipedia articles, appropriately named and organized.
