Highlight sentences over 30 words
AI finds long, complex sentences that hurt readability so you can break them up for clearer, more scannable writing.
Highlight sentences over 30 words
River's Long Sentence Highlighter identifies sentences over 30 words that may hurt readability. You paste your content, and the AI highlights lengthy sentences without making judgments or suggesting rewrites. This tool simply shows you where sentence length might create comprehension issues so you can decide which long sentences to break up for better flow and clarity. Whether you're editing blog posts, emails, or marketing copy, this tool helps you write in a scannable, accessible style.
Unlike grammar checkers that suggest random edits, we only highlight sentence length and let you decide what needs fixing. The AI counts words accurately across complex punctuation, highlights every sentence exceeding your threshold (30 words default), shows you the word count for each long sentence, and provides visibility without forcing changes. You maintain complete control over your writing style while seeing exactly where length might create problems for readability.
This tool is perfect for blog and email writers improving scannability, content marketers optimizing for online reading, professional writers making complex topics accessible, or anyone who knows long sentences hurt engagement but can't consistently catch them. If readers tell you your writing is hard to follow, or you know you write long, winding sentences, this tool helps. Use it when editing content that needs to be clear and easy to scan quickly, especially for mobile readers or busy audiences.
What Makes Long Sentences Hurt Readability
Long sentences tax reader attention and working memory. Research shows comprehension drops significantly above 25-30 words per sentence because readers struggle to hold all the information while parsing complex structures. Long sentences create several problems: readers lose track of the main point mid-sentence, they have to reread to understand, mobile reading becomes exhausting, and scannability suffers. For online content, where readers skim and attention spans are short, long sentences kill engagement. Every extra clause adds cognitive load. Readers abandon content that feels like work to process.
However, sentence length isn't about having a strict word limit. Occasional long sentences are fine for variety and rhythm. The problem is consistently long sentences that make your entire piece feel dense and difficult. Good writing varies sentence length deliberately. Short sentences create impact and emphasis. Medium sentences (15-20 words) carry most information clearly. Long sentences (25-35+ words) slow pacing and force careful reading. The best writers use all three lengths strategically. If most of your sentences exceed 30 words, your writing feels academic and inaccessible. Mix short and medium sentences to maintain energy and readability.
To evaluate whether a long sentence needs breaking, ask: Can I understand this in one reading? Does it contain multiple distinct ideas that could be separate sentences? Would breaking it up improve clarity without losing meaning? Is there a natural break point (semicolon, 'and,' 'but')? Fix long sentences when they confuse readers, pack too many ideas together, or make your writing feel heavy. Keep occasional long sentences when they flow well and maintain clarity. The goal is varied, scannable writing that respects reader attention, not mechanically chopping every sentence to 20 words.
What You Get
Every sentence over 30 words highlighted in your document
Word count displayed for each long sentence
No suggestions or rewrites, just identification
Complete control over which sentences you break up
Clear visibility into your sentence length patterns
How It Works
- 1Paste your contentCopy your writing into the workspace (100-5000 words works best)
- 2AI highlights long sentencesOur AI finds every sentence over 30 words in 30 seconds and highlights them
- 3Review flagged sentencesSee where sentence length might hurt readability and comprehension
- 4Break up when neededSplit long sentences at natural break points for clearer, more scannable writing
Frequently Asked Questions
Should I break up every sentence over 30 words?
No. The 30-word threshold is a guideline, not a rule. Some long sentences read clearly and flow well. Others pack too many ideas and confuse readers. Review each highlighted sentence and ask if it's easy to understand or if it would be clearer split up. If a 35-word sentence has good structure and natural flow, keep it. If a 32-word sentence is confusing and contains multiple distinct ideas, break it up. The goal is clarity and readability, not hitting arbitrary word counts. Use the highlights to find potential problems, then use your judgment.
How do I break up long sentences without changing my meaning?
Look for natural break points where ideas shift. Sentences with 'and,' 'but,' 'however,' 'because,' or semicolons often contain multiple ideas that can become separate sentences. For example: 'We tested five approaches, and three worked well, but two failed' becomes 'We tested five approaches. Three worked well, but two failed.' Or break after subordinate clauses: 'After analyzing the data, we found three key insights that changed our strategy' becomes 'After analyzing the data, we found three key insights. These changed our strategy.' Find the logical break point and split there.
What's the ideal sentence length for readability?
Vary your sentence length for best readability. Aim for an average of 15-20 words per sentence. Mix short (5-10 words), medium (15-20 words), and occasional longer (25-30 words) sentences. Short sentences create impact. Medium sentences carry most information clearly. Longer sentences slow pacing for complex ideas. The variety creates rhythm and maintains engagement. If you write consistently above 25 words per sentence, your content feels academic and dense. If everything is under 10 words, it feels choppy and simplistic. Variety is key.
Why 30 words specifically?
Research shows comprehension drops significantly above 25-30 words because of working memory limits. Readers struggle to hold information and parse complex structures in longer sentences. They have to reread or lose the main point. Thirty words is a practical threshold where most sentences start creating comprehension issues. Some readers handle 35-40 words fine. Others struggle above 20. Thirty words is a reasonable guideline for catching potentially problematic sentences. It's not magic, just a useful benchmark based on cognitive research and readability studies.
Does this work for all types of writing or just blogs?
Sentence length matters across all writing types, but acceptable length varies. For blogs, emails, and marketing copy (online reading), keep most sentences under 25 words. For academic or technical writing, 30-35 words is more acceptable because readers expect density. For fiction, vary widely (5-50+ words) for rhythm and style. For mobile-first content, shorter is better (under 20 words ideal). The 30-word threshold works well for business, marketing, and professional writing. Adjust your target based on your audience and medium. Online readers need shorter sentences than print readers.
What is River?
River is an AI-powered document editor that helps you write better, faster. With intelligent writing assistance, real-time collaboration, and powerful AI tools, River transforms how professionals create content.
AI-Powered Writing
Get intelligent suggestions and assistance as you write.
Professional Tools
Access specialized tools for any writing task.
Privacy-First
Your documents stay private and secure.
Ready to try Highlight sentences over 30 words?
Start using this tool in 60 seconds. No credit card required.
Highlight Long Sentences →