SmallSEOTolls where you can analyze your website for free Woorank also provides one check a day for free MOZ tools are best in paid tools but it starts from $99 per month to $599 per month but still you can get moz group buy from topseotools.tech in just $15 per month the access will be given via rdb and I am using it.
One single tool not fulfill the hole requirement, segment the process in Keyword Research (Google Keyword Planner, Übersuggest & more), Content (Copyscape, Anchor Text Over Optimization Tool (removeem)) and Technical Tools (Xenu, Backlinkwatch, Opensiteexplore, Moz, aherf, SEMrush and more). Every tools having different different features to know..and show your customer.
ScanBacklinks has on page SEO tool which sends you report and tips for website improvements. It is easy to use and points gaps in on page optimization both of your website and your competitors'.
There are many tools available for checking on page of your website like moss, SEO site checker, screaming frog, etc. You can use these tools and get the details about your on page optimization.
There are various tools to check on page optimization, Those are too helpful for on page. SEOSiteCheckup & SmallSEOTolls are one of them.
There are lots of tools available in the market but always go for manual on-page optimization process. The manual way of doing on-page optimization is very good and it helps to get the picture clear. Yes, for a quick results or an idea go for SEO Ninja Free Website Analysis Tool.
My favourite is SEMRush, however there is lots of different ones out there some free some part of a paid package. I often use other free ones just as they sometimes cover things that another tool doesn't.
There are lots of tools in the web but few are the most realiable and accurate and I would suggest SEMRush, Ahrefs, and search console for your on page.