I've posted this before but it's a nice basic tool for roughly gauging if a reading material is difficult or easy for you.
The higher the number, the "easier" the reading material. The lower the number, the "harder." So a text rated 1.8 is going to be harder to read than the text marked 2.0, and a text marked 2.6 is going to be easier. Now, this doesnt factor in if you already know X particular words that may affect what you personally find easier or harder to read, it's based on common words and amount of unique words in a text.
What you consider easier or harder is also going to depend on your current reading level - I ran a text through it that I can read extensively, got about 1.8, so I know stuff around 1.8 or easier (1.8+) is probably going to be something I can manage to read extensively. Whereas anything harder than 1.8 (so anyrhing below that from 0-1.79) is probably going to be more difficult and I'll probably need to do dictionary lookup while I read. About a year ago, my reading level was around 2.0 on this text analyzer (about where 小王子 is). So the stuff I'm reading extensively at 1.8 now, I used to need a dictionary to read and they were more challenging to read.