Automated scans can immediately help website owners detect several accessibility issues, but it’s important to remember that scans are extremely limited in the number of accessibility issues that can be successfully flagged.
In other words, while scans are helpful, they are limited and all results must be reviewed.
Scans are available for free so there is no need to buy a premium scan.
Here are the automated scans we recommend:

Web Accessibility Evaluation (WAVE) tool by WebAIM.org
