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Run-On Sentence Checker

Find sentences that are too long, fused, or spliced

0 words

Tame Your Longest Sentences Before Readers Give Up

Long sentences are not automatically wrong, but they are where most readability problems hide. A 50-word sentence forces readers to hold multiple ideas in working memory at once, and if the grammar slips — a missing conjunction, a comma where a period belongs — comprehension breaks down. This tool measures every sentence in your text, flags the ones that exceed safe thresholds, and gives you a visual map of where your prose gets dense.

The Color System

Green sentences (25 words or fewer) are easy to read by any audience. Yellow sentences (26 to 35 words) are fine if well-structured but worth a second look. Orange sentences (36 to 50 words) are getting difficult — check for proper connectors. Red sentences (over 50 words) are almost certainly too long for a single sentence and likely contain run-on errors or could benefit from splitting.

Fixing Run-On Sentences

The simplest fix is a period. Find where two complete thoughts meet and split them. If the ideas are closely related, use a semicolon. If one idea depends on the other, use a subordinating conjunction like"because,""although," or"when" to make the relationship explicit. Avoid fixing run-ons with just a comma — that creates a comma splice, which is itself a run-on error.

Sentence Variety

Good writing mixes sentence lengths. A paragraph of only short sentences feels choppy and childish. A paragraph of only long sentences feels exhausting. The distribution chart shows whether you have healthy variety or whether your sentences cluster at one length. Aim for a bell curve centered around 15 to 20 words with occasional short and long outliers for rhythm.

Privacy

All processing runs in your browser. No text is transmitted or stored.

$ faq

What is a run-on sentence? ▸
A run-on sentence is two or more independent clauses joined without proper punctuation or a conjunction."I went to the store I bought milk" is a fused sentence — two complete thoughts with no separator."I went to the store, I bought milk" is a comma splice — a comma alone cannot join two independent clauses. Both are run-on errors. This tool flags long sentences that likely contain these problems.
How does this tool detect run-on sentences? ▸
The tool splits your text into sentences, counts words in each, and flags sentences that exceed length thresholds. Sentences over 30 words are marked as long, over 40 as very long, and over 50 as likely run-ons. It also checks for comma splices by looking for patterns where a comma separates what appear to be two independent clauses (subject-verb patterns on both sides).
Are all long sentences run-on sentences? ▸
No. A long sentence can be grammatically correct if it uses proper conjunctions (and, but, or), semicolons, or subordinating conjunctions (because, although, while). A 40-word sentence with clear structure and proper connectors is fine. The tool flags length as a risk indicator — longer sentences are more likely to contain run-on errors and are harder for readers to follow regardless of grammar.
What sentence length should I aim for? ▸
Most readability guidelines recommend an average sentence length of 15 to 20 words. Individual sentences can vary — some as short as 3 words, others up to 30 — but the average should stay in that range. If your average exceeds 25 words, readers will struggle to follow your ideas. Mix short punchy sentences with longer complex ones for the best rhythm.
How do I fix a run-on sentence? ▸
Four common fixes: split it into two sentences with a period; join the clauses with a semicolon if they are closely related; add a coordinating conjunction (and, but, or, so) after a comma; or restructure using a subordinating conjunction (because, although, when) to make one clause dependent. Choose the fix that best preserves your intended meaning and rhythm.
Does this tool catch comma splices? ▸
The tool uses a heuristic pattern to detect likely comma splices — commas followed by a pronoun or common subject word and then a verb. This catches many comma splices but is not a full grammar parser. Review each flagged instance in context to confirm whether it is a genuine splice or an acceptable comma usage like a list or appositive.
Is any data sent to a server? ▸
No. All processing happens locally in your browser using JavaScript. Your text is never transmitted or stored.