Automated SEO tools, performance audits and accessibility scanners are useful. I run several of them on every client site as a starting point. They find a lot in five minutes that would take me hours.
What they catch reliably
Technical issues. Broken links, missing meta tags, slow-loading images, render-blocking scripts, mobile responsiveness errors. Anything with a clear pass-fail answer. A scanner is faster than I am and does not miss things.
Common patterns. The 50 most frequent SEO mistakes. The standard accessibility violations. The performance issues that crop up on every site. If your problem is on a list, the tool finds it.
Things that have changed since the last scan. Useful for ongoing monitoring. The tool tells you when a Core Web Vitals score has dropped or when a new redirect chain has appeared.
What they miss
The strategic question. A tool can tell you the homepage has a high bounce rate. It cannot tell you whether the homepage is the wrong landing page for your paid traffic. The tool sees the symptom. The diagnosis takes context.
Whether what you have is right for what you sell. A tool will not tell you that the service page leads with the wrong benefit, or that the call to action is asking for the wrong commitment too early. That is a content judgment, not a technical one.
The competitive landscape. The tool scans your site in isolation. It does not look at how your site compares to the three competitors you actually lose deals to.
The bits that are working but could be better. Tools focus on errors. They do not flag the page that is doing well but could double its conversion with a small change.
Use the tool. Then have someone read what the tool found and tell you what it means. The tool is the starting point, not the finished work.
If you have run a tool and are wondering what to do with the output, that is the conversation.