Text Inspector is the professional online tool for analysing texts with a range of tools

You can analyse your text in terms of:
-key statistics about text length, syllables and so on
-the loading of difficult words in your text
-Lexical Diversity
-many other metrics.
You can use Text Inspector free for short texts.
On the menu, click on each tool to see what it does and how to use it.
If you want to use larger texts and more tools you can subscribe from a few pounds/dollars a month.