One of the features of Wikipedia's best articles that sets them apart from much of the Internet is the skill with which they are verified (WP:V) and reliably sourced (WP:RS); these processes are derived from policy and guideline, respectively. Wikipedia's authority on the Internet partly relies on its attention to these two issues. Like all of Wikipedia's content, featured article candidates (FACs), featured list candidates (FLCs) and good article nominees (GANs) are scrutinized by reviewers for their grounding in sources our readers can rely on. This is explicitly reinforced in FA Criterion 1c, in the lead of the FL criteria, in Good Article Criterion 2 and at peer review. FA Criterion 2c also stipulates that featured articles should have consistently formatted inline citations.

Determining what makes a source reliable and text verifiable is often not a straightforward task, and can require considered judgement; but this process is within the reach of all good Wikipedian writers. This dispatch sets out advice for how to evaluate sources – especially for nominators and reviewers at Wikipedia's content review pages. This is not an exhaustive list, but aims to help Wikipedians to acquire the necessary skills.

When evaluating sources, look at how the source is being used; contentious statements or anything related to a living person require a high-quality source. Exceptional claims, even if they aren't about living people, require high-quality reliable sources and will draw scrutiny.

Citing sources

Content sourced to books, magazines, newspapers, and other published sources should specify the title and publisher, as well as author, date of publication and location within the work when available. Usually, "location" means a page range, but for small works or articles this may not be necessary. The edition of the work (3rd ed., revised) is needed, as revisions of a source can change it substantially.

For web pages, the needs are similar: publisher, title, and date of last access are the bare minimum, and author and publication date should be given when available.

If a citation is missing publisher information or page numbers, text may be hard to verify and reliability is difficult to evaluate; before approaching FAC, make sure all of your sources are complete and consistently cited, as required by Criterion 2c and Wikipedia's citing examples. GAN does not have a requirement for consistently formatted citations, but consistency may increase the impression of authority and accuracy in an article.

Reliable sources

WP:RS says "Articles should be based on reliable, third-party, published sources with a reputation for fact-checking and accuracy." Websites may receive more scrutiny than books, magazines or newspapers; while printed sources are also checked, it can be harder to judge reliability on websites, and so they often warrant extra attention. Explicit opinion pieces in newspapers and magazines need to be assessed in relation to the overall balance in an article, in line with the WP:NPOV policy.

Printed sources

For books or other printed sources – including albums and DVDs that relate directly to the topic – the following warrant closer scrutiny of the sources:

• A publisher that is unrecognized or located outside the usual publishing locations (for example, New York City)
• An article that uses mostly printed sources, but where important information is missing from the citations.
• Vanity presses.

In some popular-culture articles, a bias against printed sources may be detected. Printed sources are often more reliable than online sources, and there is no reason not to use them where they are available.

Websites

The following are some things reviewers can check in citations sourced to websites:

• Run your cursor over the links and double check that they include publisher information from trusted sources (such as the BBC, The New York Times, USA Today, International Herald Tribune, etc.). Spot-check the actual sites to check quality and to see that the title, author and publication date are correct; this tool is helpful.)
• Click through to articles that lack publisher information.
• Check all websites you don't recognize:

• If a site is backed by a large media company or is a media or official organization, it may be reliable, depending on the text being cited.
• If a site has an "about us" page, "contact us" or FAQ page, check those for information about how the site gathers information.
• If a site is written by a noted expert who has been independently published by reliable sources in the field, or is hosted by a college or university institute concerned with the field, it may be reliable, depending on the text cited or whether there should be other, more reliable (for example, peer-reviewed) sources available.

• Government sites connected to the field may be reliable.
• Paid sites that rely on the accuracy of their information for their living (for example, such as Equibase) are usually reliable, although they may be questioned.
• Some sites have proven reliable for some purposes: examples include (but are not limited to) IGN, CNET and Cricinfo.
• If the site gives its sources, but still seems like a personal site, it should be questioned. Depending on the text that is being sourced, it could be reliable, but all self-published sources must meet WP:SPS.

Websites with the following attributes should be questioned:

• Lacks a page describing how information is gathered, or is a fan or contributor site.
• Looks like a personal webpage (including but not limited to tripod.com, geocities.com, members.aol.com and anything that is written by an individual or fans).
• Has a highly commercial feel, or prominent advertising such as the planting of multiple annoying popups on your screen before you can even find the "about us" page.
• Gets some or all of its information from Wikipedia or a Wikipedia mirror (this is regarded as circular).
• Is a usenet posting or an archive of usenet postings.
• Is a forum post.
• Is a blog.
• Is a page from About.com, unless the author is an expert independently published in the field.
• Is a page from IMDb, used for anything beyond the very basics of a film's cast or awards; even then, you're better off just referencing the film or the awards site.

Responding to queries about reliable sources

Reviewers need to know what sort of reputation for accuracy, fact checking and editorial oversight the website has. You can establish this by showing:

• A page on the site that gives their rules for submissions that indicate fact-checking and editorial oversight.
• They are backed by a media company, university or institute with a reputation for fact-checking and editorial oversight.
• Third-party publications from reliable sources that support the site as a self-published source or that the author is a noted expert in their field.
• The author is a member of the press with a reputation for reliability.

Meeting these criteria doesn't necessarily mean a source is reliable (depending on the text cited) or that you've used the best sources, but they do set a minimum threshold you should be prepared to meet.

Things that won't help:

• Saying "I know it's reliable": reviewers need to know why it is considered reliable according to policy.
• Saying "It has an article on Wikipedia": Wikipedia is not a reliable source.
• Saying "So-and-so WikiProject says it's reliable": the Project needs to demonstrate reliability for each source, and reliability depends on the text being cited. An example that addresses Wikipedia's policy on self-published sources is at the Gilbert and Sullivan Project page.
• Saying "It's used in 15 other featured articles": OtherStuffExists isn't a valid argument.