Luckily, the international nonprofit World Wide Web Consortium (W3C) brings together smart people who develop open standards to ensure the long-term growth of the Web. They produce recommendations for making websites fair and equally accessible for the highest number of people possible. Their Web Content Accessibility Guidelines (WCAG) 2.1 offer clear guidance for web developers to achieve ADA compliance.
I should mention one caveat to all of this. Businesses that are required to comply but don't have the ability to bring their websites into compliance can provide an accessible alternative to provide the same information, goods, and services that they provide online, like a staffed phone line. The trick, however, is that this option has to provide at least equal access, including in terms of hours of operation. And, as we know, the internet is around 24/7, so good luck with that. 

All public-facing websites should evaluate and consider compliance with ADA laws related to their industry. That is, your website should aim to be accessible to users with a disability. Failure to comply with this requirement can lead to potential legal issues and challenges, particularly in some industries. Fortunately for WordPress site owners, there are at least a dozen plug-ins specially designed to help you achieve greater measures of ADA compliance with minimal costs and work involved. The following are five options to consider to make your WordPress website ADA compliant.
President George H.W. Bush signed the Americans with Disabilities Act into law July 26, 1990. The ADA prohibits discrimination of people with disabilities and guarantees the same opportunities as everyone else. These opportunities include employment possibilities, purchasing of goods and services and the ability to participate in State and local government programs.
Through the Americans with Disabilities Act (ADA), our nation committed itself to eliminating discrimination against people with disabilities. The U.S. Department of Justice’s (DOJ) Civil Rights Division is proud to play a critical role in enforcing the ADA, working towards a future in which all the doors are open to equality of opportunity, full participation, independent living, integration and economic self-sufficiency for persons with disabilities. 

Hey Casey, this is one of the areas where things get a little weird because the W3 doesn’t actually have any say over the ADA guidelines, it is more than the ADA guidelines adopted the WCAG 2.0 guidelines as just that, a guideline to help. As far as I know, the tool you’ve linked to hasn’t been used in any judgements I’m aware of. Usually when it comes down to making a decision on if something is/isn’t compliant they have people use the actual PAWS tools and show what elements do/don’t work as intended or are otherwise inaccessible. Hope this helps!
Finally, WA11Y is another top ADA compliance plug-in to consider. A toolbox of resources to help you meet most ADA compliance needs, the plug-in packs multiple accessibility tools, each with a unique purpose. Tota11y, the first tool in the box, for instance, annotates all elements of your web pages and identifies any accessibility issues. Another tool in the box, WAVE, performs a detailed accessibility analysis of each page and provides printable reports. Then, you have FILTERS which is used to modify data within Wa11y.
The guidelines are broken down by four main principles: perceivable, operable, understandable, and robust. Under each principle, there are guidelines that provide specific goals a website should work toward. Under each guideline, there are testable success criteria. Those criteria are graded A, AA, or AAA. This grade shows the level of conformity to accessibility, AAA being the highest. The law only requires A and AA guidelines to be met.