Web Vocabulary Profiler
Here's a great tool if you want to get an idea of how readable or comprehensible a text is. You can also use it to help you create a text that is more readable. The online tool uses Paul Nation's word frequency lists to give you a breakdown of which words from your text fit into which list. Give it a go... It sounds more complicated that it actually is.
Just copy and paste in your text and submit. Have fun.
Best regards from the ALEC team