Readability Score Calculator - Free Online Text Readability Checker

Readability scores translate structure—how long your sentences are, how heavy your words are, and sometimes whether vocabulary looks “familiar” to a standard list—into numbers editors, teachers, and compliance teams can compare across drafts. They do not measure how interesting, accurate, or ethical your ideas are; they estimate how much effort a typical reader may need to decode the surface of the text on a first pass. That still matters for SEO because search engines reward pages that satisfy intent; when visitors bounce quickly or skim without engaging, weak clarity can undermine even perfect keyword placement. Educators use the same metrics to align worksheets and parent communications with developmental reading expectations, while accessibility advocates pair plain language with structural cues such as headings and lists so cognitive load stays predictable on mobile screens. SynthQuery’s Readability Score Calculator is a free, client-side text utility. Paste marketing copy, help-center articles, lecture notes, policy excerpts, or localization drafts and instantly see seven classical indices—Flesch Reading Ease, Flesch–Kincaid Grade Level, Gunning Fog, Coleman–Liau, SMOG, the Automated Readability Index, and the Dale–Chall Readability Score—alongside word, sentence, and paragraph statistics, averages for words per sentence, syllables per word, and characters per word, plus an estimated reading time. A color-coded difficulty summary translates the Flesch Reading Ease band into plain English (easy, medium, or hard), while the composite grade blends multiple grade-style formulas so you can discuss audience fit with stakeholders. Sentence highlights flag long or dense lines, and the suggestions panel points to specific sentences, simpler word swaps, and paragraphs that may need subheadings or bullets. Nothing is uploaded for scoring: the arithmetic runs in your browser, which keeps drafts private while you iterate.

Seven formulas appear together so you can see divergence instead of trusting a lone headline number. Flesch Reading Ease and Flesch–Kincaid Grade Level share syllable and sentence inputs but express different scales—one for quick “how comfortable,” the other for “approximate grade.” Gunning Fog emphasizes polysyllabic vocabulary, which is why abstract marketing language spikes it faster than conversational prose. Coleman–Liau uses characters per word and sentences per word, which can disagree with syllable-heavy methods when acronyms or Roman numerals dominate. SMOG was designed around health-education passages and reacts strongly to three-syllable words. The Automated Readability Index blends character counts with words per sentence for another grade proxy. Dale–Chall compares every token against the New Dale–Chall (1995) familiar word list: words absent from that list count as “difficult,” and the classic formula converts difficult-word percentage plus average sentence length into an adjusted score mapped to grade bands. Beyond the numbers, the interface operationalizes diagnosis. Sentence highlights tint long sentences amber and dense sentences with a warmer tint so you can see rhythm issues without exporting to another editor. The suggestions module lists up to eight long sentences, offers editorial synonym hints for a curated set of polysyllabic business words, and flags paragraphs that exceed size thresholds. Target reading level compares a composite grade—averaging multiple grade proxies including Dale–Chall’s band—to the grade you select, with tolerance messaging that acknowledges real-world variance. Comparison mode duplicates the dashboard for two buffers so growth teams can pit legacy copy against a plain-language rewrite. Local export covers UTF-8 text and a lightweight PDF built with jsPDF so nothing leaves your machine for the core math.

Each formula is a regression-style model fit to twentieth-century comprehension studies; they correlate with understanding but do not measure truth, nuance, or cultural context. Flesch Reading Ease combines words per sentence and syllables per word inside linear coefficients anchored at 206.835 minus penalties. Flesch–Kincaid Grade Level applies different weights to the same two ratios. Gunning Fog adds the percentage of complex (typically three-plus syllable) words. Coleman–Liau estimates grade from letters per hundred words minus sentences per hundred words with its own intercept. SMOG uses a square-root term on polysyllables scaled by sentence count. ARI mixes mean characters per word with words per sentence. Dale–Chall uses the percentage of words not found in the published familiar list plus average sentence length, adding a constant when difficult words exceed five percent of tokens. Because browsers lack a pronunciation API, syllable counting uses vowel-group heuristics: strip punctuation, trim some silent-style endings, count contiguous vowel clusters, and enforce at least one syllable per token. Hyphenated compounds, acronyms, and loanwords may disagree with dictionary syllabification—compare revisions of the same document rather than chasing parity with every vendor. Tokenization treats word boundaries with apostrophes as single tokens so contractions align with the Dale–Chall list. For SEO, readability complements crawl hygiene, structured data, internal linking, and Core Web Vitals; treat it as a UX lever layered on top of solid information architecture.

SEO editors paste final body copy before publication to confirm a general-interest article has not crept into graduate-level density after expert quotes and citations land. They pair readability with intent checks: a lucid answer that matches the query and loads quickly still outranks keyword stuffing inside impenetrable paragraphs. Academic authors use the tool on abstracts, impact statements, or public summaries while leaving methods sections alone—discipline-specific vocabulary will raise indices even when the prose is correct for peers. Technical writers score installation guides and API intros meant for mixed audiences, exporting PDFs for release folders while logging average sentence length in retrospectives. Marketing teams compare hero variants in Compare mode to see whether “premium” tone accidentally doubled average syllables per word. Legal and compliance teams reference plain-language programs that expect documented readability evidence; this calculator supplies reproducible numbers, though it cannot replace attorney review. UX writers test error strings and empty states so stressed users see short sentences and familiar words. Localization managers split multilingual drafts by language before scoring because syllable heuristics and the Dale–Chall list target English. Accessibility specialists pair quantitative targets with semantic HTML—WCAG does not mandate a specific grade score, but cognitive accessibility often benefits from both.

Use this page when you need reproducible readability evidence without sending drafts to a third-party API. Work from a clean paste of the prose readers will actually see, then iterate with highlights and exports until the composite grade matches your audience brief. The numbered steps below mirror the in-app workflow so teammates can follow the same checklist in reviews or compliance tickets.

Syllable heuristics miscount some proper nouns, chemical names, and non-English phrases; split multilingual drafts before scoring. Poetry, dialogue without closing punctuation, and bullet lists without terminal periods can skew sentence counts—add punctuation if you need stable segmentation. Synonym suggestions are editorial hints, not automatic rewrites; sometimes jargon should stay for precision. Medical, legal, and regulatory teams must still follow institutional plain-language standards beyond any automated score.