Sentence Length Analyser
Paste your essay, report or any text to instantly analyse sentence lengths, detect variety, flag overly long sentences and identify repetitive patterns. Pro Mode adds readability scores, a length chart, heatmap, paragraph breakdown and improvement suggestions.
How to Use the Sentence Length Analyser
From a blank box to a full variety score — no signup, nothing ever leaves your browser.
Everything above runs entirely in your browser — your text is never uploaded to a server, so it stays completely private from start to finish.
Sentence Length Analyser — Free Sentence Length Checker
A sentence length analyser measures every sentence in a text and scores how much they vary, so you can spot monotonous rhythm and overly long sentences at a glance. This one updates live as you type, runs entirely in your browser, and never uploads your text to a server.
Two paragraphs can have the exact same word count and read completely differently — one flows, the other feels flat or exhausting, and the difference usually comes down to sentence length variety rather than word choice. This sentence length checker measures every sentence individually, flags anything over 35 words as too long, and scores overall variety on a 0-100 scale so the pattern is visible at a glance rather than something you have to sense by ear. Pro Mode extends this into full readability scoring (Flesch, Flesch-Kincaid Grade Level, and Gunning Fog), a visual length chart and heatmap, a repetition detector for consecutive same-length sentences, and specific, sentence-by-sentence improvement suggestions.
1Simple vs Pro — What Each Mode Includes
| Feature | Simple Mode | Pro Mode (Free) |
|---|---|---|
| Live sentence count, average & extremes | ✓ | ✓ |
| Sentence variety score with visual ring | ✓ | ✓ |
| Length distribution & sentence-by-sentence breakdown | ✓ | ✓ |
| Highlight mode & TXT download | ✓ | ✓ |
| Upload TXT, DOCX, PDF, MD or RTF files | ✓ | ✓ |
| Flesch, Flesch-Kincaid & Gunning Fog readability scores | — | ✓ |
| Length distribution chart & sentence heatmap | — | ✓ |
| Consecutive same-length repetition detector | — | ✓ |
| Best/worst sentence comparison & suggestions | — | ✓ |
| Paragraph breakdown & CSV export | — | ✓ |
2Common Reasons People Check Sentence Length
Writing teachers flag sentence length monotony as a specific, fixable habit distinct from grammar or vocabulary — a student can write correct sentences and still produce prose that feels tiring to read simply because every sentence runs the same length. The Purdue Online Writing Lab's guidance on sentence clarity makes a related point about varying structure to keep readers engaged. Editors use the same check in reverse for professional copy: catching the moment a document accidentally shifts from crisp short sentences into a run of long, clause-heavy ones without the writer noticing it happened.
3Sentence Length Categories
| Category | Word Range | Reading Effect |
|---|---|---|
| Short | 1-12 words | Punchy, easy to scan — overuse can feel choppy |
| Medium | 13-25 words | The workhorse range for most general writing |
| Long | 26-35 words | Fine for building an idea, harder to follow in sequence |
| Very long | 36+ words | Often a sign the sentence needs splitting |
A good variety score isn't about hitting a specific average — it's about the spread across these four bands. A paragraph that's entirely medium-length sentences can score poorly on variety even though every individual sentence looks reasonable, because the lack of contrast between them is exactly what reads as monotonous.
4Understanding the Gunning Fog Index
The Gunning Fog Index, one of the readability scores available in Pro Mode, was developed by American businessman Robert Gunning in 1952 after he became convinced that most public and business writing was needlessly dense. The formula combines average sentence length with the percentage of "complex" words — those with three or more syllables — into a single number representing the years of formal education a reader needs to understand the text on a first pass. A score of 8 means the text should be understandable by an eighth grader; general-audience writing typically targets a fog index under 12, and scores above 17 suggest graduate-level complexity.
Every count, variety score, and Pro feature — including readability scoring and the heatmap — runs entirely in your browser using JavaScript. Nothing you type is ever sent to a server.
5Frequently Asked Questions
Grounded in established readability research — Gunning Fog Index figures follow Wikipedia's summary of Robert Gunning's original 1952 formula, with additional readability formula background from ReadabilityFormulas.com's detailed breakdown.
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