Readability Checker

Each formula estimates readability using a slightly different mathematical approach, so seeing them together gives a more reliable picture than any single score alone. Flesch Reading Ease produces a 0-100 score (higher = easier) based on sentence and word length. Flesch-Kincaid Grade Level and Gunning Fog Index both estimate a U.S. school grade level needed to understand the text, but weight complex/long words differently. SMOG Index specifically estimates the grade level needed to fully comprehend a text (originally designed for health-literacy materials, where full comprehension matters more than skimming ability). Coleman-Liau Index estimates grade level using character counts instead of syllable counts, which makes it fast to compute and less sensitive to imperfect syllable counting. In practice, if most of these scores agree, you can trust the overall pattern; if they diverge significantly, your text likely has an unusual mix of very long/short sentences or words.

Syllable counting uses a widely-used heuristic: it counts groups of consecutive vowels (a, e, i, o, u, y) in each word, then applies a small correction for silent trailing 'e' (so 'like' counts as 1 syllable, not 2). This approach is fast, works entirely client-side without a dictionary lookup, and is accurate for the vast majority of common English words — it's the same general technique used by most readability tools, including well-known ones. It can occasionally miscount unusual words, contractions, or words borrowed from other languages, but these edge cases have a negligible effect on the overall scores for any text longer than a sentence or two, since the formulas work on averages across your whole text.

It depends entirely on your audience, but as a general guide: 90-100 is very easy (readable by an average 11-year-old), 60-70 is considered 'standard' or 'plain English' (comfortable for most adult readers, and a common target for general-audience web content), 30-50 is difficult (roughly college level), and below 30 is very difficult (best suited to academic or specialist audiences already familiar with the subject). Most style guides for web and marketing content recommend targeting 60 or above, since a majority of internet readers — including native speakers — read more comfortably and skim more effectively at that level, even when they're capable of understanding more difficult text.

Each formula was developed independently, using different source texts and slightly different weighting of sentence length versus word complexity, so some disagreement between them is normal and expected — even professionally published readability research typically reports a range rather than treating any single formula as the definitive answer. A text with a few very long technical terms but otherwise short sentences might score high on syllable-sensitive formulas (Gunning Fog, SMOG) while scoring more moderately on Coleman-Liau, which weighs character count instead. Rather than chasing one specific number, look at whether all five scores broadly agree with your intended audience's reading level — that agreement (or lack of it) is more informative than any single formula in isolation.

The suggestions panel targets the specific factors driving your scores, but the two highest-impact, most universal changes are: shortening your average sentence length (splitting compound sentences joined by 'and' or 'which' into two separate sentences is usually the single fastest win), and replacing long, multi-syllable words with shorter, more common synonyms where the meaning doesn't suffer ('use' instead of 'utilize', 'help' instead of 'facilitate'). Both directly and heavily influence every one of the five formulas at once, since sentence length and word/syllable length are the two core inputs every formula in this tool is built from.

No — readability formulas are purely mechanical, measuring only sentence length and word/syllable complexity; they say nothing about grammar correctness, logical structure, tone, persuasiveness, factual accuracy, or overall writing quality. A grammatically awkward but short-sentenced text can score as 'easy,' while a beautifully structured piece with a few necessarily technical terms can score as 'difficult.' Treat these scores as one useful signal about accessibility for a general audience, not a complete judgment of whether the writing is good — they're most valuable as a quick, objective check alongside your own editorial judgment, not a replacement for it.

No — every formula here (Flesch Reading Ease, Flesch-Kincaid, Gunning Fog, SMOG, and Coleman-Liau) was developed and calibrated specifically for English, based on English syllable patterns, average word lengths, and English-reading grade-level benchmarks. Running non-English text through this tool will produce numbers, but they won't correspond to meaningful reading-difficulty levels in that language, since syllable structure and typical sentence patterns vary significantly between languages. For non-English content, look for readability formulas specifically designed and calibrated for that language instead.

No. Every calculation — syllable counting, sentence splitting, and all five readability formulas — runs entirely inside your browser using plain JavaScript, with no server-side component involved at any point. This means the tool keeps working with no internet connection once the page has loaded, and it's safe to check readability on unpublished drafts, internal documents, or anything else you'd rather not send anywhere.