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.
A-Class articles are assessed by two editors within the project to determine that they are close to featured article status. Submit a request for an assessment the same way you would for a B-class article; the only difference is two reviewers will assess it.
More detailed criteria
Articles should be checked against the following criteria:
Well-written: The article is well-written and contains no spelling or grammatical errors, it adheres to the relevant sections of the manual of style
Comprehensive: The article covers every relevant aspect of its subject in sufficient detail, including background information, but is not unnecessarily long due to trivial or irrelevant information
Referencing and citation: The article is supported with inline citations to reliable sources for all claims, and these citations are appropriately formatted
Neutral: The article is accurate and unbiased, none of its content is disputed, and it is not the subject of any edit warring
Structure: The article is well structured, consisting of a lead which summarizes the rest of the article, and a reasonable number of sections containing more detailed information
Media: The article contains images relevant to the illustrate subject, accompanied with captions and alt text
Additionally, the article should meet all B-class criteria
Very useful to readers. A fairly complete treatment of the subject. A non-expert in the subject matter would typically find nothing wanting.
Expert knowledge may be needed to "tweak" the article, and style issues may need addressing. 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 (although not equalling) the quality of a professional encyclopedia.
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 is mostly complete, without major issues, but requires some further work to reach Good Article standards.
More detailed criteria
The article meets the following criteria:
Referencing and citation: The article is suitably referenced, with inline citations where necessary. The citations are not just raw URLs
Coverage and accuracy: The article reasonably covers the topic, and does not contain obvious omissions or inaccuracies.
Structure: The article has a defined structure. This should consist of a lead section and appropriately divided sections.
Grammar and style: The article is reasonably well-written. There are no significant errors in spelling or grammar, and no outstanding cleanup issues
Supporting materials: The article contains supporting materials where appropriate. This should include relevant images if any are available, and an infobox if one exists.
Additionally, that the article should meet all the C class criteria
No reader should be 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, and expert knowledge is increasingly needed. The inclusion of supporting materials should also be considered if practical, and the article checked for general compliance with the manual of style.
The article meets B1 or B2 as well as B3 and B4 and B5 of the B-Class criteria.
More detailed criteria
The article meets the following criteria:
Referencing and citation: The article is suitably referenced, with inline citations where necessary. The citations are not just raw URLs
Coverage and accuracy: The article reasonably covers the topic, and does not contain obvious omissions or inaccuracies. Some aspects, particularly the background, may still be covered in less detail than would be desirable, however no critical information should be absent.
Structure: The article has a defined structure. This should consist of a lead section and appropriately divided sections.
Grammar and style: The article is reasonably well-written. There are no significant errors in spelling or grammar, and no outstanding cleanup issues
Supporting materials: The article contains supporting materials where appropriate. This should include relevant images if any are available, and an infobox if one exists.
Accessibility: The article presents its content in an appropriately understandable way although it should not be "dumbed down". Technical terms should be explained or at least linked.
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 address cleanup issues.
The article has a meaningful amount of good content, but it is still weak in many areas, may lack one or more key elements, and may require serious cleanup. It should have at least one serious element of content, and should not meet the definition of a stub.
More detailed criteria
The article has a usable amount of good content, but it is weak in many areas, usually in referencing. Quality of the prose may be distinctly unencyclopedic, and MoS compliance non-existent; but the article should satisfy fundamental content policies such as notability and BLP, and provide enough sources to establish verifiability. No Start-Class article should be in any danger of being speedily deleted.
Provides some meaningful content, but the majority of readers will need more.
Provision of references to reliable sources should be prioritised; the article will also need substantial improvements in content and organisation.
The article is either a very short article or a rough collection of information which will require a large amount of work to achieve recognition. It meets the general definition of a Stub.
More detailed criteria
The article is either a very short article or a rough collection of information that will need much work to become a meaningful article. It is usually very short, but can be of any length if the material is irrelevant or incomprehensible.
Provides very little meaningful content; may be little more than a dictionary definition
Any editing or additional material can be helpful. The provision of meaningful content should be a priority.
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; 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.
Meets the criteria of a Stand-alone List, 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.
Categories (along with other features like cross-references, lists, and infoboxes) help users find information, even if they don't know that it exists or what it's called.
Be aware not to over-categorise and to be careful of maintaining a neutral point of view when creating or filling categories. Make decisions about the structure of categories and subcategories that make it easy for users to browse through similar articles.
Images are used to help explain articles by providing examples of style, lay-out, logo, or other typical visual aspects. Many images are fair use and should be used sparingly. Public domain or Creative Commons / GFDL licensed images can be used more freely.
Editors need to ensure that images have correct licenses, fair use rationales (where applicable), and are only used in articles for which they have such rationale. Fair use images should not be used as pure decoration.
Is any type of template. The most common types of template used in the WikiProject are infoboxes and navboxes.
Serves different purposes depending upon the type of template. Infoboxes go at the upper right of a page and are a way of providing easy access to important pieces of introductory infomation about the subject. Navboxes normally go across the very bottom of a page, and are for the purpose of uniting a group of related articles into an easily accessible format for inclusion on every page listed in the navbox.
Beware of too many different templates, as well as templates that give either too little, too much, or too specialized information.