Run-On Sentence Checker
A free, fast, and proven that detects run-on sentences — including comma splices and fused sentences — and offers one-click, readable fixes as you type. Ideal for essays, emails, and assignments.
Tip: Add two independent clauses joined only by a comma (e.g., “It was late, we kept working.”) to see a comma splice flagged.
How to Use
- Paste or type your sentence(s) into the box above.
- Check the colored status pill next to each sentence (green = OK; red = potential run-on).
- Review the suggested rewrites and pick the one that fits your style and context.
Tips & Notes
- Comma splice: two independent clauses joined by a comma without a coordinating conjunction.
- Fused sentence: two independent clauses jammed together with no comma, conjunction, or semicolon.
- Acceptable alternatives: use a period, a semicolon, or a comma + FANBOYS (for, and, nor, but, or, yet, so).
- Transitional adverbs (however, therefore, moreover) usually need a semicolon before and a comma after when joining clauses.
FAQ
What is a run-on sentence? A sentence where two or more independent clauses are joined incorrectly — typically a comma splice or a fused sentence.
How do I check if my sentence is correct?
Paste your sentence into the box above. Each sentence is analyzed in real time. If we detect a run-on (comma splice or fused sentence), we flag it and show fixes such as a period, semicolon, or comma + FANBOYS.
Do I have run-on sentences?
Run each sentence through the checker. A red status pill means we found a potential issue; expand the suggestions and choose a fix that fits your style and meaning.
How do I solve a run-on sentence?
- Split into two sentences with a period.
- Join with a semicolon (clause; clause).
- Use a comma + FANBOYS (for/and/nor/but/or/yet/so).
- Subordinate one clause (e.g., because, although, when).
- Use an em dash for emphasis (sparingly).
What are the 5 rules to fix a run-on sentence?
- Period: break into two sentences.
- Semicolon: link closely related clauses.
- Comma + coordinating conjunction (FANBOYS).
- Subordinating conjunction to make one clause dependent.
- Colon (when the second clause explains or expands the first).
How do I practice identifying run-ons?
- Find the subjects and finite verbs — if you have two complete clauses, check how they’re joined.
- Scan for a comma sitting alone between full clauses — that’s often a comma splice.
- Read aloud and pause at punctuation; if you stumble, you may need a stronger break.
Does this tool check for comma splices?
Yes. It acts as a comma splice checker by spotting clauses joined only with a comma and suggesting semicolons, periods, or comma + FANBOYS.
Does this detect fused sentences?
Yes. If two independent clauses are jammed together with no punctuation or conjunction, we flag a fused sentence and propose clean rewrites.
Is this a run-on sentence checker, corrector, fixer, or detector?
All of the above. It’s a run-on sentence checker/detector that also works as a corrector/fixer by offering ready-to-use rewrites.
How do I identify a sentence fragment (not a run-on)?
A fragment looks like a sentence but lacks a subject or a finite verb (or doesn’t express a complete thought). Our tool focuses on run-ons, but this tip helps you tell them apart.
What is a semicolon used for?
A semicolon links two closely related independent clauses without a conjunction: We revised the draft; the deadline was tonight.
Does Grammarly check for run-on sentences?
Most general grammar checkers can flag run-ons. This page provides a focused, transparent checker with readable, classroom-friendly fixes you can copy.
Example — Comma splice (❌) and fixes (✅):
It was late, we kept working. ❌ It was late, so we kept working. ✅ It was late; we kept working. ✅ It was late. We kept working. ✅
Example — Fused sentence (❌) and fixes (✅):
She finished the draft she sent it to the editor. ❌ She finished the draft, and she sent it to the editor. ✅ She finished the draft; she sent it to the editor. ✅ After she finished the draft, she sent it to the editor. ✅