Why Grammarly and ProWritingAid Are Making Your Writing Worse

I’ve used both ProWritingAid and Grammarly across hundreds of projects. The Only Grammar Book You’ll Ever Need They’re useful tools with serious limitations that most writers don’t understand until the tools have already damaged their writing. Here’s what these grammar checkers actually do well, what they get wrong, and why you can’t trust them with your final draft.

What They Actually Do Well

Grammar checkers catch the mechanical errors your eyes skip over after you’ve been staring at the same document for hours. Misspelled words, doubled words, basic subject-verb agreement problems, missing periods. The stuff that spell check has handled since the 1990s, but slightly better. They’re also useful for spotting passive voice overuse, though even that feature triggers false positives constantly.

For first-draft cleanup, they save time. Running a document through Grammarly or ProWritingAid before you start real editing catches the obvious debris so you can focus on what actually matters: whether the writing is clear, specific, and doing its job.

That’s where the usefulness ends.

Why Do Grammar Checkers Get Commas Wrong?

Both tools are terrible with commas. This is their most common failure and the one that damages the most writing. They flag commas that are correct and suggest commas that are wrong. They can’t reliably distinguish between restrictive and nonrestrictive clauses. They don’t understand that comma usage in fiction, where rhythm and pacing matter, follows different conventions than comma usage in business writing.

The Oxford comma alone causes chaos. If you use it consistently, Grammarly sometimes flags it. If you don’t use it, ProWritingAid sometimes inserts it. Neither tool maintains consistent comma rules across a full document because neither tool truly understands your intent. They’re pattern-matching against statistical models, not applying grammatical logic.

Writers who accept comma suggestions without evaluating each one end up with documents full of comma errors that weren’t there before the grammar checker touched them. I’ve seen manuscripts where the author ran the text through Grammarly and accepted every suggestion, and the result had more errors than the original draft.

Do Grammar Checkers Destroy Your Voice?

This is the problem professional writers understand and casual users don’t. Grammar checkers optimize for standard formal English. They flag sentence fragments, intentional repetition, conversational tone, dialect, and any construction that deviates from textbook grammar. For business emails and academic papers, that’s fine. For anything with a voice – fiction, memoir, blog posts, marketing copy – it’s destructive.

Grammarly will flag a sentence fragment that you wrote deliberately for emphasis. ProWritingAid will suggest restructuring a short punchy sentence into a longer grammatically complete one that loses all its impact. Both tools will try to “fix” dialogue that’s intentionally informal because the character speaks informally. Accept those suggestions and your writing sounds like it was generated by committee.

I clean up AI-generated content regularly, and one of the telltale signs is writing that’s grammatically perfect and completely lifeless. Grammar checkers push human writing in the same direction. They sand off the edges that make writing sound like a specific person instead of a generic content mill.

They Trigger AI Detection Filters

Here’s a problem most writers don’t know about until it costs them. Grammar checker suggestions push your writing toward the same patterns AI generates: safe word choices, standard sentence structures, formal tone, no personality. Accept enough suggestions from Grammarly or ProWritingAid and your writing starts looking like machine output to AI detection tools like Originality.ai.

This is increasingly a real-world problem. Publishers, academic institutions, and clients are running content through AI detectors. If your human-written work gets flagged because you let a grammar checker sand it into generic standard English, you’re in trouble. The irony is brutal: you used a tool to “improve” your writing, and the improvement made it look like a robot wrote it.

The reason is straightforward. AI language models and grammar checkers are trained on similar datasets and optimize for similar patterns. They both prefer common word choices over unusual ones, standard constructions over idiosyncratic ones, and formal register over conversational. When you accept their suggestions systematically, you’re steering your writing toward the statistical center of English prose – which is exactly where AI-generated text lives.

They Can’t Read Context

Grammar checkers analyze sentences. There is more in my Writing Hub. They don’t read paragraphs, sections, or documents. They can’t tell whether a word choice that seems unusual is actually the right word for the context. They can’t tell whether a sentence that breaks a grammar rule is breaking it for a reason. They flag the word “impact” as a noun-versus-verb issue without understanding that the usage has been standard English for decades.

ProWritingAid’s style reports are better than Grammarly’s for long-form writing. The pacing analysis and sentence length variation reports can surface real issues. But the tool still can’t tell you whether your chapter is boring, whether your argument is convincing, or whether your opening paragraph gives the reader a reason to keep reading. Those are writing problems, not grammar problems, and no software solves them.

The Real Danger: Writers Who Trust Them

The worst thing about grammar checkers is what they do to writers who treat them as authorities. I’ve worked with clients who accepted every Grammarly suggestion for years and genuinely believed their writing was improving. It wasn’t. They were training themselves to write in the tool’s preferred style: safe, formal, generic, and stripped of personality. Their writing got more correct and less readable at the same time.

When Grammarly, ProWritingAid, and a human editor disagree, the human editor is right almost every time. The tools are useful for catching typos and mechanical errors. They are not editors. They don’t understand your audience, your purpose, your tone, or the specific rules of your genre. A professional editor does.

How to Use Them Without Letting Them Ruin Your Writing

Use them early in your editing process, not late. Run your draft through the tool to catch obvious errors, then turn it off and do your real editing by hand or with a human editor.

Never accept suggestions in bulk. Evaluate every single suggestion individually. If you can’t explain why the tool’s suggestion is better than what you wrote, keep what you wrote.

Turn off style suggestions when editing fiction, memoir, or anything with a distinctive voice. Use the grammar and spelling checks only. The style suggestions will homogenize your writing into something that sounds like everyone else.

Don’t use grammar checkers as a substitute for learning grammar. If you don’t understand why a comma goes where it goes, a tool that sometimes puts commas in the wrong place isn’t going to teach you. Pick up a copy of Strunk and White, or read enough well-edited prose that you internalize the patterns. There’s no shortcut for that.

And if you’re writing something that matters – a book, a major proposal, website copy that represents your business – hire a human editor. Grammar checkers cost $20 a month. A professional editor costs more and is worth every dollar because they understand what your writing is trying to do, not just whether it follows rules.