Spellcheck is great. Grammarly’s even better. But if you think those tools are catching everything, think again.
Grammar checkers are designed to catch obvious slip-ups, including misspelled words, missing punctuation, and some awkward phrasing. But they can’t replace a trained eye or a deep understanding of how language works. In fact, some of the most distracting, credibility-killing mistakes in your writing will still pass right through even the most advanced grammar tool.
That’s why readers (and editors) notice issues that software won’t.
In this article, we’ll walk through the top writing mistakes that grammar checkers miss—and show you how to catch them yourself before your readers do.
1. Word Confusion (They’re, Their, There… and Beyond)
Grammar checkers are great at catching typos, but they’re terrible at spotting correctly spelled words used in the wrong context. These are called homophones or easily confused words, and they can completely change the meaning of your sentence without triggering any warning from your software.
Common real-world mix-ups that grammar checkers often miss:
- ❌ Their going to the store later.
✅ Should be: They’re going to the store later. - ❌ Your the best friend I’ve ever had.
✅ Should be: You’re the best friend I’ve ever had. - ❌ He gave me a nice complement on my outfit.
✅ Should be: compliment - ❌ That color really compliments the room.
✅ Should be: complements - ❌ The weather will effect your plans.
✅ Should be: affect - ❌ The affect was immediate.
✅ Should be: effect
Why it matters:
Even though these sentences are technically spelled correctly, they’re still wrong, and they trip up readers. Grammar tools often won’t catch them because they look "normal" on the surface.
How to fix it:
Slow down during edits and read for meaning, not just spelling. If you’re unsure about a word, look it up—even pros do this. Better safe than accidentally “complementing” someone’s curtains.
2. Misused Apostrophes
Apostrophes cause more confusion than almost any other punctuation mark, and grammar checkers are notoriously bad at spotting when you’ve used them wrong.
The two most common offenders:
Its vs. It’s
- ✅ It’s = contraction for it is or it has
Example: It’s going to be a long night. - ✅ Its = possessive, showing ownership
Example: The dog wagged its tail.
❌ Mistake: The company updated it’s website last week.
✅ Correction: The company updated its website last week.
Grammar checkers rarely flag this, even when it completely changes the sentence’s meaning.
🔹 Plural vs. Possessive Apostrophes
- ✅ The dogs = more than one dog
- ✅ The dog’s leash = the leash belonging to one dog
- ✅ The dogs’ leashes = leashes belonging to multiple dogs
❌ Mistake: All the student’s handed in their homework.
✅ Correction: All the students handed in their homework.
Why it matters:
Misused apostrophes are one of the first things readers and editors notice. They’re small, but they stand out, and they send a message that the writing wasn’t carefully reviewed.
How to fix it:
During revision, search for every apostrophe in your draft. Ask: Is this a contraction? Possessive? Or a plural word that doesn’t need an apostrophe at all?
3. Comma Splices and Run-Ons
Comma splices and run-on sentences often “sound fine” in your head, but they break grammar rules and make your writing look rushed or unpolished. Unfortunately, grammar checkers rarely catch them unless they’re extreme.
🔹 What’s a comma splice?
A comma splice happens when two complete sentences (independent clauses) are joined by a comma without a coordinating conjunction.
❌ Example: She finished the draft, he started editing it.
✅ Fix: She finished the draft, and he started editing it.
✅ Or: She finished the draft. He started editing it.
✅ Or: She finished the draft; he started editing it.
🔹 What’s a run-on sentence?
A run-on is two or more independent clauses stuck together without any punctuation or conjunction.
❌ Example: I love writing it clears my head.
✅ Fix: I love writing because it clears my head.
✅ Or: I love writing. It clears my head.
Why grammar checkers miss it:
If the sentence has correct spelling and a comma, software often assumes it’s fine, especially if it mimics natural speech. But readers pick up on the awkwardness, even if they can’t name the rule.
How to fix it:
- Read your work aloud slowly to catch awkward joins
- Watch for independent clauses joined by only commas or nothing at all
- Use conjunctions, punctuation, or sentence breaks intentionally
4. Weak Word Choices That Aren’t Technically Wrong
Here’s the tricky part: your sentence might be grammatically correct, but still fall flat. Grammar checkers won’t flag weak, vague, or overused words—because they’re not “wrong.” But readers? They feel the dullness immediately.
🔹 Common weak words that pass unnoticed:
- Very, really, just, quite, a bit, somewhat
- Got, did, went, made, had, was, is
❌ She was very tired after the trip.
✅ She collapsed onto the bed, drained from the trip.
❌ He did a great job on the project.
✅ He nailed the project from start to finish.
These “weak” words don’t break grammar rules, but they don’t carry much weight either. They rely on telling rather than showing, and they strip your prose of energy and precision.
Why grammar checkers miss it:
Most grammar tools don’t understand tone, context, or impact. As long as the sentence is structurally sound, the checker sees nothing wrong—even if your reader is yawning.
How to fix it:
- Highlight every instance of very, just, or really in your draft and challenge yourself to replace or delete it
- Swap vague verbs for sharper, more specific actions
- Ask: Can I show this instead of telling it?
5. Sentence Structure Repetition
Even if your grammar is perfect, your writing can still feel flat and mechanical if every sentence follows the same pattern. Grammar checkers almost never flag this because technically, there’s nothing wrong. But to readers, it’s boring.
🔹 What repetitive structure looks like:
She grabbed her coat. She opened the door. She stepped outside.
Each sentence starts with the subject (she), then a verb. While this structure is fine in isolation, stacked back-to-back, it creates a robotic rhythm that drains energy from your prose.
🔹 What it sounds like:
- Predictable
- Monotonous
- Choppy or overly simplistic
Why grammar checkers miss it:
They focus on correctness, not cadence. Repetitive sentence structure isn’t a grammar error, but it’s a huge style problem.
How to fix it:
- Vary sentence length and rhythm
- Start with prepositional phrases, transition words, or action tags
- Mix short punchy lines with longer, more complex ones
✅ Grabbing her coat, she stepped into the hallway. The wind met her at the door, sharp and sudden. She hesitated, then pushed outside.
Tip: Read your work aloud. If it sounds like a metronome, it needs variety.
Why Relying on Software Alone Hurts Your Writing
Grammar checkers are powerful tools—they catch typos, flag obvious errors, and save time. But they’re just that: tools. They don’t understand your voice, tone, or the subtle rhythms that make writing sing.
What software can’t do:
- Detect context-based mistakes like word confusion or misused apostrophes
- Recognize when sentence structure is repetitive or weak
- Understand tone or style preferences
- Catch every punctuation nuance, like comma splices in natural speech
Relying solely on grammar tools can lull you into a false sense of security, letting distracting errors slip through and dulling your unique writing voice.
The best approach:
- Use grammar checkers for a first pass, but always follow up with careful self-editing
- Read your work aloud to catch rhythm and flow issues
- Consider feedback from real readers or editors who understand the craft
Grammar checkers are valuable helpers, but they aren’t perfect. Many subtle mistakes slip through, from word misuse to punctuation errors to flat, repetitive prose.
The best writers combine these tools with their own careful reading, editing, and understanding of language. When you go beyond the software, your writing becomes clearer, stronger, and truly your own.
Keep learning, keep revising, and trust your voice—because readers always will.