Media Bias/Fact Check (MBFC) is an American website founded in 2015 by Dave M. Van Zandt. MBFC uses an explicit methodology to rate media outlets.  It considers four main categories and multiple subcategories in assessing the "Political bias" and "Factual Reporting" of each source. 

It is widely used, and has sometimes been criticised for its methodology.  Scientific studies using its ratings note that ratings from Media Bias/Fact Check show high agreement with an independent fact checking dataset from 2017, with NewsGuard and with BuzzFeed journalists.

Methodology 
Four main categories are used by MBFC to assess political bias and factuality of a source. These are:  (1) use of wording and headlines (2) fact-checking and sourcing (3) choice of stories and (4) political affiliation. MBFC additionally considers subcategories such as bias by omission, bias by source selection, and loaded use of language. A source's "Factual Reporting" is rated on a seven-point scale from "Very high" down to "Very low". 

Political bias ratings are American-centric
 and include "Extreme left", "Left", "Left center", "Least biased", "Right center", "Right", and "Extreme right".

The category "Pro-science" is used to indicate "evidence based" or "legitimate science". MBFC also associates sources with warning categories such as "Conspiracy/Pseudoscience", "Questionable Sources" and "Satire".

Fact checks are carried out by independent reviewers who are associated with the International Fact-Checking Network (IFCN) and follow the International Fact-Checking Network Fact-checkers’ Code of Principles, which was developed by the Poynter Institute. 
A source may be credited with high "Factual Reporting" and still show "Political bias" in its presentation of those facts, for example, through its use of  emotional language.

Reception 
Media Bias/Fact Check is widely used in studies of mainstream media, social media, and disinformation. The occurrence and patterns of misinformation differ depending on the platform involved. Media Bias/Fact Check has been used in both single- and cross-platform studies of platforms including TikTok, 4chan, Reddit, Twitter, Facebook, Instagram, and Google Web Search.

A comparison of  five fact checking datasets frequently used as "groundtruth lists" has suggested that choosing one groundtruth list over another has little impact on the evaluation of online content.
In some cases, MBFC has been selected because it categorizes sources using a larger range of labels than other rating services.
MBFC offers the largest dataset covering biased and low factual news sources.  Over a 4-year span, the percentage of links that could be categorized with MBFC was found to be very consistent. Research also suggests that the bias and factualness of a news source are unlikely to change over time.

When MBFC factualness ratings of ‘mostly factual’ or higher were compared to an independent fact checking dataset's ‘verified’ and ‘suspicious’ news sources, the two datasets showed  “almost perfect” inter-rater reliability.
A 2022 study that evaluated sharing of URLs on Twitter and Facebook in March and April of 2020 and 2019, to compare the prevalence of misinformation, reports that scores from MediaBiasFactCheck [sic] correlate strongly with those from NewsGuard (r = 0.81).  
Another study reports high agreement between ratings from Media Bias Fact Check [sic] and BuzzFeed journalists.

The site has been used by researchers at the University of Michigan to create a tool called the "Iffy Quotient", which draws data from Media Bias/Fact Check and NewsWhip to track the prevalence of "fake news" and questionable sources on social media.

Writers at the Poynter Institute, which develops PolitiFact, have stated that  "Media Bias/Fact Check is a widely cited source for news stories and even studies about misinformation, despite the fact that its method is in no way scientific." In 2018, a writer in the Columbia Journalism Review described Media Bias/Fact Check as "an armchair media analysis" and characterized their assessments as "subjective assessments [that] leave room for human biases, or even simple inconsistencies, to creep in". A study published in Scientific Reports wrote: "While [Media Bias/Fact Check's] credibility is sometimes questioned, it has been regarded as accurate enough to be used as ground-truth for e.g. media bias classifiers, fake news studies, and automatic fact-checking systems."

See also 
 Ad Fontes Media
 AllSides
 NewsGuard

References

External links 
 

Fact-checking websites
Internet properties established in 2015
Criticism of journalism
Media bias