It depends on your audience. A score of 60–70 is considered "plain English" — comfortable for most adult readers with a high school education. Consumer-facing content (blog posts, product descriptions, emails) should target 60–80. Academic journals typically score 20–40. Legal and technical documents often score below 20. The US Department of Defense requires military training materials to score at least 60.

Each formula measures readability using different proxies — syllable count, character count, or percentage of complex words. They agree closely for standard prose but diverge when text contains many long words, abbreviations, or unusual sentence structures. This is normal and expected. Use the average of the grade-level scores for a more robust estimate, or use Flesch Reading Ease as your primary benchmark.

The formulas become reliable with 100+ words. With fewer words, statistical variance is high — a single unusually long sentence can swing the grade level by 2–3 grades. For representative scores, use a full paragraph of at least 10 sentences. For very short text like headlines or CTAs, readability scores are not a meaningful measure — focus on clarity and impact instead.

Grade 7–9 (Flesch-Kincaid) is the industry sweet spot for general content blogs, SaaS landing pages, and consumer-facing documentation. This matches the average US adult reading level. Technical developer content can comfortably target Grade 10–13. If you are writing for students, healthcare patients, or non-native English speakers, aim for Grade 5–7.

The Gunning Fog formula penalizes "complex words" — defined as words with three or more syllables — more aggressively than the syllable-per-word ratio used in the Flesch formulas. Content that uses many polysyllabic technical terms (like "authentication", "infrastructure", or "optimization") will score significantly higher on Gunning Fog than on Flesch-Kincaid, even if the sentence structure is simple.

No. All five readability calculations — syllable counting, word segmentation, sentence detection, and formula computation — run entirely in JavaScript within your browser. Your text is never transmitted to any server. You can disconnect from the internet after the page loads and the tool will continue working.

The formulas were designed for English and produce unreliable results for other languages. The syllable-counting algorithm specifically targets English phonology. For other Latin-alphabet languages (Spanish, French, German), results will be approximate at best. For non-Latin scripts (Chinese, Arabic, Cyrillic), character and word counts will be inaccurate.