What punctuation errors does a checker catch?

A punctuation checker catches missing commas (especially before conjunctions in compound sentences), incorrect apostrophes (it's vs its, your vs you're), run-on sentences that need a period or semicolon, missing periods at the end of sentences, incorrect semicolon or colon usage, double punctuation marks, and spaces before punctuation marks. Most tools also flag inconsistent use of serial commas (Oxford comma).

Is the Oxford comma required?

The Oxford comma (the comma before 'and' in a list of three or more items) is not strictly required in all style guides. AP style omits it. Chicago, APA, and most academic styles include it. The classic example: 'I love my parents, Batman and Wonder Woman' (without Oxford comma, it sounds like your parents are Batman and Wonder Woman). 'I love my parents, Batman, and Wonder Woman' (with Oxford comma, clearly three separate items). When in doubt, include it. It rarely causes confusion, while omitting it sometimes does.

When do I use a semicolon?

A semicolon connects two complete sentences that are closely related. 'I finished the report; my coworker reviewed it.' Each side of the semicolon must be a complete sentence on its own. If either side is a fragment, use a comma instead. Do not use a semicolon before 'and' or 'but'. That is what a comma is for.

Punctuation checker online free: fix commas, periods, and apostrophes

Last updated: April 20268 min readAI Tools

Spelling errors are obvious. Grammar mistakes stand out if you know the rules. But punctuation errors? Those are the ones that slip past you. A missing comma changes meaning. A wrong apostrophe makes you look careless. A run-on sentence loses your reader three clauses in.

Paste your text into the checker below. It flags every punctuation issue with a suggested fix. Takes about 3 seconds.

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The 8 most common punctuation mistakes

1. Missing comma before a conjunction in a compound sentence

Wrong: I finished the project and my boss reviewed it.

Right: I finished the project, and my boss reviewed it.

When two complete sentences are joined by "and," "but," "or," "so," or "yet," put a comma before the conjunction. If the second part is not a complete sentence (no subject), skip the comma.

2. It's vs its

Wrong: The company changed it's policy.

Right: The company changed its policy.

"It's" always means "it is" or "it has." "Its" (no apostrophe) shows possession. This is the opposite of what you might expect, because normally apostrophes show possession (the dog's bone). "Its" is the exception.

3. Your vs you're

Wrong: Your going to love this.

Right: You're going to love this.

"You're" = "you are." "Your" = belonging to you. Same rule as it's/its. If you can substitute "you are" into the sentence and it still makes sense, use "you're."

4. Run-on sentences

Wrong: I went to the store I bought milk I came home.

Right: I went to the store. I bought milk. I came home.

Three independent clauses need something between them. Periods, semicolons, or commas with conjunctions. Just running them together is a run-on.

5. Comma splices

Wrong: The meeting ended early, everyone went home.

Right: The meeting ended early, so everyone went home.

Two complete sentences cannot be joined with just a comma. You need a conjunction (and, but, so, yet), a semicolon, or a period.

6. Apostrophes in plurals

Wrong: The dog's are in the yard. We have three car's.

Right: The dogs are in the yard. We have three cars.

Apostrophes are for possession (the dog's bone) or contractions (don't, can't). Never for making a word plural. This is called the "grocer's apostrophe" because it shows up on signs ("Apple's $1.99").

7. Semicolons where commas belong

Wrong: I like coffee; tea; and juice.

Right: I like coffee, tea, and juice.

Semicolons separate complete sentences or items in a list when the items themselves contain commas. They do not replace commas in simple lists.

8. Missing periods and double spaces

Sounds minor. But missing a period at the end of a paragraph, or leaving double spaces between sentences, signals carelessness. The checker catches both.

Quick punctuation rules reference

Mark	Use	Example
,	Separate items, before conjunctions, after introductory phrases	After the meeting, we left.
.	End a sentence	That is all.
;	Connect two related complete sentences	It rained; we stayed inside.
:	Introduce a list, explanation, or example	You need three things: time, effort, and patience.
'	Contractions and possession	It's the dog's toy.
" "	Direct quotes, titles of articles/short works	She said, "Let's go."
-	Compound adjectives before a noun	A well-known author.

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