What can we do to ensure a fully compliant a11y application? Unfortunately, you won't be able to manage it with just some tools. For instance, none of the tools we selected pointed out that we should add a name to the input fields, as pointed out by an ARIA rule (see https://w3c.github.io/using-aria/#fifth for more on it). Also, there are some conditions that cannot be tested in code. For example, guidelines say that error or mandatory fields should not be highlighted just with color (because of color blindness) but should have some external text or mark; how would you test for that in an automated way? take a look at the following screenshot for an example, taken from https://govuk-elements.herokuapp.com/errors/example-form-validation-multiple-questions, with enhanced visibility for errors:

It's not possible to get an A, AA, or AAA level without an audit, but you can add more tools to help out with that:

• The W3C Web Accessibility Initiative provides an extensive list of tools (113, as of today!) at https://www.w3.org/WAI/ER/tools/
• The A11Y Project provides a community effort to simplify web accessibility, showing several useful techniques, at https://a11yproject.com/
• MDN has a full overview of ARIA, a spec from the W3C geared to providing extra information for screen readers by way of the usage of HTML attributes, at https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques
• The W3C also provides many suggestions for using ARIA, including samples of code, at https://w3c.github.io/using-aria/
• There are several accessibility checkers, for all main browsers, which can diagnose a page on the go, so just search for them; some work as browser extensions, while others are code meant to be added to your website, to detect and report possible problems

Even if no single tool or set of tools can ensure a11y compliance, you will be able to build yourself a good starting lot of tools; experiment a bit!