Automated tools are a great first pass for accessibility - these tools can help you more quickly identify what work you may have to do in a Guide.
The Web Accessibility Initiative (W3C) provides a comprehensive list of accessibility tools and resources to help you select the right tools for your needs. Below are some recommended tools for general automated accessibility testing:
WAVE Accessibility Evaluation Tool
The WAVE extensions allow you to evaluate web content for accessibility issues directly within your browser.
SiteImprove for Chrome
The Siteimprove Accessibility Checker allows you to easily check the accessibility of any web page directly in Google Chrome, so you can immediately identify issues based on the latest ACT (Accessibility Conformance Testing) rules – with instant feedback and recommendations.
axe DevTools® Chrome or Firefox extension
The free axe DevTools browser extension is ideal for individual developers and testers to find and fix common accessibility issues.