Rhythm, not just length
Readers tire of very long sentences, but a page of short ones sounds like a list. Good prose varies its rhythm: a long sentence that builds an idea, then a short one that lands it.
This checker does two things:
- Highlights sentences over your long threshold (25 words by default) and very long threshold (40 words).
- Charts every sentence so you can see the shape of your writing at a glance (clusters of long bars are where readers struggle; flat rows of identical bars are where they get bored).
The Variety score compares the spread of sentence lengths with their average (the coefficient of variation). “Low” means your sentences are all about the same length.
Splitting long sentences
- Break at conjunctions: and, but, which, because.
- Move asides in parentheses or between dashes into their own sentence.
- Turn lists inside a sentence into a bulleted list.
For context: guidance from GOV.UK suggests sentences of no more than about 25 words for public-facing content, and many newspaper style guides aim for an average around 20.
Worked example
Here is what the Sentence Length Checker returns for its built-in example. Click Try an example in the tool above to load it, then change it as you like.
Short sentences land. But when a writer strings together clause after clause, adding qualifications, asides and examples without ever pausing to let the reader catch up, the sentence becomes a test of memory rather than a vehicle for meaning. Vary the rhythm. A long sentence can build an idea carefully, layer by layer, and then a short one can deliver the point.| Found | Type | Suggestion |
|---|---|---|
| “But when a writer strings together clause after clause, adding qualifications, a” | Long | — |
Questions
How long is too long for a sentence?
For general readers, sentences over about 25 words start to get hard, and over 40 words are very hard. Aim for an average of 15–20 words with plenty of variation.
What is a run-on sentence?
Strictly, two independent clauses joined without proper punctuation. Informally, any overly long sentence. This tool finds long sentences; the grammar checker catches some comma splices.
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