Readability formulas estimate text difficulty from measurable signals such as sentence length and word complexity.
Flesch Reading Ease is useful for directional benchmarking on websites and editorial pages.
Flesch-Kincaid estimates grade level and is practical for setting broad audience targets.
Gunning Fog highlights complexity concentration and is helpful for business and policy prose.
SMOG focuses on polysyllabic density and is useful in more formal content environments.
Coleman-Liau and ARI use character and sentence ratios to estimate reading load in digital writing.
No formula can fully validate factual accuracy or legal precision. Use them as triage tools, not absolute quality gates.
Best practice is combining formula scores with issue-level diagnostics and before/after review.