According to The Literacy Project, about 50% of American adults cannot read above an eighth grade level (and 45 million are “functionally illiterate” and cannot read above fifth-grade stuff). Point: Simplify your copy.
That’s what this free online readability tester by WebFX helps with. It quickly analyzes and gives your copy a grade-level assessment. You can copy and paste text for it to test, but I particularly like its ability to work with webpages—give it a URL, and it does its thing.
I had it evaluate a fairly short Toolbox post, and it gave a score of 60.1 (0 is difficult, and 100 is easy to read). In plain language: “It should be easily understood by 12 to 13 year olds.” Good, it’s right there in the desired ballpark.