by Adam Chaboryk on WordPress.org
Geared towards content authors, Sa11y straightforwardly identifies accessibility issues at the source.

Logged-in view with Sa11y showing heading hierarchy and non-descriptive link text errors.
Sa11y is an accessibility quality assurance tool that visually highlights common accessibility and usability issues. Geared towards content authors, Sa11y straightforwardly identifies errors or warnings at the source with a simple tooltip on how to fix them.
Sa11y works in Preview mode.
Visit the project website for a demo or to learn more!