Hello, forum. Could you tell me how I can check the quality of external links pointing to my website? Which ones are dofollow and which are nofollow? Which ones are useful, and which ones should I remove? What services are available for this? Preferably free or low-cost ones. I’m interested in your experience and best practices. Thank you for your attention.
Like Denka already said, GSC and Ahrefs webmaster tools are enough, in particular the second one. AWT shows if the links are do follow, no follow or spam. You just have to add a snippet in your header.php to start getting results. Of course, some options are limited in the free version, but trust me, you'll like what you'll see even in the standard build.
In this respect, I would concentrate more on the context. A good indicator that the link works is when its presence has logical explanations rather than serving only SEO. The difference between do-follow and no-follow does matter but not that much as many say. It is even possible to have a positive use from no-follow links. When it comes to testing, Search Console is a nice choice, while another common tool might be used to get the overall picture of things.