As Gary says, it depends. If you’re content to do a bit of superficial and potentially inaccurate testing, there are dozens, perhaps hundreds of tools of varying complexity. However, even if you use them all, and use them correctly, you can only do perhaps 30% of the tests required for a proper WCAG audit. bear in mind that the EAA mandates conformance with EN 301 549, which goes a long way beyond WCAG.
Tools can’t get you anywhere near that. The Cypress.io video is disgraceful - they know or should know the limitations of what their tool can do.
To do a complete, accurate WCAG audit requires a detailed understanding of the 55 level A and AA success criteria and the techniques for testing them. In many cases, the appropriate technique depends on how features are coded, so you need a “toolbox” of at least a couple of hundred techniques to draw from.
Don’t trust tools
Tools can help, but they only provide information. The pass / fail decision MUST be based on inspection of the code and the user interface. Never take the result from a tool at face value because they are frequently wrong. We increasingly build our own tools so at least we know when they may be misleading.
It’s really difficult
To get to a reasonable level of competence requires thousands of hours of learning and even more experience i.e. somewhere in the range of 10,000 to 20,000 hours. We don’t even interview people with less than 10 years’ full time accessibility testing experience. I mention this to give some context to what a functionality tester can expect to achieve if they only do a few hours of accessibility testing here and there. There’s some low hanging fruit, but it gets really difficult after that.
Bookmarklets
We use loads of individual ones from various sources as well as writing our own. The following are some useful collections.
Browser extensions
We use loads of single-purpose extensions, such as for freezing the DOM or applying custom CSS. We also use these WCAG testing extensions.
Other tools
Website Error Checker: Accessibility & Link Checker - SortSite (crawls websites and tests every page)
Colour Contrast Analyser (CCA) - TPGi
PDF Accessibility Checker - PAC (for PDFs)
CommonLook PDF Validator: PDF Accessibility Checker | FREE Download (for PDFs)