Free Run-on Sentence Checker
A run-on sentence is two or more independent clauses joined without proper punctuation — or a sentence so long it loses the reader. This checker flags sentences over 25 words, comma splices, and fused sentences that need a period or semicolon. For undercooked sentences (the opposite problem), use the Fragment or Sentence Checker. For total counts, see the Sentence Counter.
Flagged Issues
How the Run-on Sentence Checker Works
The checker analyzes each sentence in three ways: word count (over 25 words = warning), comma splice detection (independent clause + comma + independent clause with no conjunction), and fused-sentence detection (multiple independent clauses with no punctuation).
Rules & Best Practices
1Aim for under 25 words per sentence
Sentences under 25 words score in the 'easy to read' band on most readability indices. Going much higher loses readers.
2Comma splice = error
Two independent clauses joined by only a comma is wrong: 'I came, I saw.' Fix with a semicolon, period, or coordinating conjunction.
3Fused sentences need punctuation
'I went to the store I bought milk' is fused. Add a period: 'I went to the store. I bought milk.' Or a comma + conjunction: 'I went to the store, and I bought milk.'
4Split long sentences
If a sentence runs over 30 words with multiple 'and's and commas, split it. The reader will thank you.
Polish Your Writing
Combine grammar checks with our Character Counter and Word Counter for a full text analysis — counts, frequency, and structure.
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