Comma Splice Checker
Paste a draft and the checker highlights every comma that seems to join two complete clauses — the error handbooks call a comma splice — then explains why it flagged the comma and offers three rewrites. It is a rule-based heuristic, so it separates likely splices from possible ones and leaves the decision to you. Free, no sign-up.
Runs entirely in your browser — your text is never uploaded.
Paste or type some text to see its likely comma splices — two complete clauses joined by only a comma.
How to Use the Comma Splice Checker
- Paste your text. A paragraph is enough, and a whole draft works too. The check runs in your browser as you type.
- Read the two colours. Rose marks a likely splice: both sides of the comma look like complete sentences. Amber marks a possible one — the clauses are very short, they open the same way, or several in a row are joined by commas — which is sometimes a deliberate style choice. Hover over a highlight for the reason.
- Open the cards under the text. Each flagged comma shows the clause before it, the clause after it, and three rewrites: two sentences, a semicolon, or a comma and a conjunction. Copy the one that fits.
- Decide. The checker proposes, you judge. Read the sentence aloud with the fix in place and keep the version that says what you mean.
What a Comma Splice Is
A comma splice joins two independent clauses — each with its own subject and verb, each able to stand alone as a sentence — with nothing but a comma. The survey closed on Friday, it had reached 400 responses is a splice: The survey closed on Friday and It had reached 400 responses are both complete sentences, and a comma is too weak to hold them together. Purdue OWL's handouts on clauses and run-ons list the same three repairs most handbooks give, plus a fourth that changes the structure.
- Make two sentences. The survey closed on Friday. It had reached 400 responses. Safest, and often the clearest.
- Use a semicolon. The survey closed on Friday; it had reached 400 responses. Best when the two ideas are closely connected.
- Add a coordinating conjunction. A comma plus for, and, nor, but, or, yet or so is correct: The survey closed on Friday, and it had reached 400 responses.
- Subordinate one clause. When the survey closed on Friday, it had reached 400 responses. This makes one clause depend on the other and usually shows the logic best.
The Trap with “However” and “Therefore”
Words such as however, therefore, thus, moreover, consequently, furthermore, nevertheless and otherwise look like conjunctions, but they are conjunctive adverbs, and a comma before one does not join two clauses. The sample was small, however, the effect was large is a splice. Write The sample was small; however, the effect was large (semicolon before, comma after) or make two sentences. The checker looks for exactly this pattern and shows the repaired sentence with the missing comma added after the adverb. Compare The method, however, is slow: there however interrupts one clause, nothing is spliced, and the checker leaves it alone.
What the Checker Flags — and What It Does Not
There is no grammar parser here, only rules. For every comma followed by a space, it asks whether the words before it can stand alone and whether the words after it start a new clause: a subject pronoun and a verb (it had reached), there is/are, this/these plus a verb, a noun phrase followed by its verb (the effect was large), a name followed by a verb, or one of the conjunctive adverbs above followed by any of these. It stays silent when a coordinating conjunction follows the comma, when the left side opens with a subordinator (although, because, when, if), a preposition or an introductory word (however, first, honestly), when the comma sits inside quotation marks or brackets, when a speech tag follows (“…,” he said), and when the commas end a series of clauses with and (She came, she saw, and she conquered), which handbooks allow.
| Situation | What happens | Why |
|---|---|---|
| A clause opens with a verb the checker does not know | Missed (false negative) | Verbs are recognised from a list of common verbs and regular endings, not by tagging every word. |
| Fused sentences with no punctuation at all | Not checked | The checker only examines commas; a fused sentence has none to examine. |
| A deliberate run of short clauses (I came, I saw) | Flagged as possible | Many handbooks accept short, parallel clauses; the page marks them so you can choose. |
| A list of clause-like items after a colon | Sometimes flagged | Without a parser, a list of full clauses and a run of splices look alike. |
| Unquoted speech or a title that contains a comma | Sometimes flagged | Only text inside quotation marks is skipped. |
How Accurate Is It?
On two hand-written test sets — textbook-style splices mixed with commas that look like splices but are not — it found every splice but one on its first run over the held-out set and flagged none of the correct sentences. Those are short, tidy sentences, so treat the figures as a ceiling. On roughly 9,400 sentences of edited prose from this site's own guides, it raised about one flag per thousand sentences, and most of those were lists or titles rather than splices. Student drafts contain more splices and messier grammar, so expect it to miss some. Use it as a second pair of eyes, not a verdict.
Worked Example
The Try an example paragraph has 83 words, 8 sentences and 10 commas. The checker flags 5 of the sentences — 2 as likely splices and 3 as possible — and leaves Although the sample was small, the effect was large and The team repeated the study, but the effect disappeared alone, because the first begins with a subordinator and the second joins its clauses with but. Here is one flagged sentence with each fix:
Original
Most participants were students, however, a few were staff.
Two sentences
Most participants were students. However, a few were staff.
Semicolon
Most participants were students; however, a few were staff.
Conjunction
Most participants were students, but a few were staff.
Frequently Asked Questions
- What is a comma splice?
- A comma splice is two independent clauses joined by only a comma, as in It rained all weekend, the match was cancelled. Each half could be a sentence on its own, so the comma is too weak a join. Fix it with a period, a semicolon, a comma plus a coordinating conjunction, or by making one clause dependent.
- Is a comma before “however” a comma splice?
- Yes, when it joins two complete clauses: The sample was small, however, the effect was large. “However” is a conjunctive adverb, not a conjunction. Use a semicolon before it and a comma after it, or start a new sentence. If “however” merely interrupts one clause (The method, however, is slow), there is no splice.
- What is the difference between a comma splice and a run-on sentence?
- “Run-on” is the broader label for independent clauses that are joined wrongly. A comma splice is the run-on with a comma between the clauses; a fused sentence is the run-on with no punctuation at all. This checker examines commas, so it finds splices but not fused sentences.
- Is a comma splice ever acceptable?
- Sometimes. Several handbooks allow commas between very short, closely parallel clauses (I came, I saw, I conquered), and fiction and speeches use them for rhythm. In academic writing, take the safe route and use a period or semicolon unless you are quoting. The checker marks short and parallel clauses as possible so you can decide.
- Does the checker catch every comma splice?
- No. It recognises the second clause by its opening words and a list of common verbs, so a clause that begins with an unusual noun or verb can slip through. It also cannot see fused sentences, which have no comma. Read the flagged sentences, but do not treat an empty result as proof your draft is clean.
- How do I fix a comma splice without changing my meaning?
- Pick the repair that matches the relationship between the ideas. A period gives each idea its own sentence; a semicolon signals that they belong together; and, but, so or yet names the relationship (addition, contrast, result); and a subordinator such as because or although shows which idea matters more. Read the result aloud before you keep it.
- Is my text uploaded anywhere?
- No. The checker runs entirely in your browser; nothing you paste is sent to a server or stored.