Testing Grammarly is something most business writers do at some point, usually after an embarrassing typo slips through or a colleague mentions the tool in passing. The questions that follow are always the same: does it catch the things that matter, does it make your writing better, and is the paid plan worth the price over the free one? This article answers all three, drawing on the kinds of writing tasks that come up daily in professional settings: emails, reports, proposals, and executive summaries.
What Grammarly actually checks
Grammarly runs several overlapping checks whenever you paste in text or use its browser extension. The free tier covers spelling, basic grammar, and punctuation. The paid tier (called Grammarly Pro) adds tone detection, clarity rewrites, plagiarism checking, and more detailed style suggestions.
In practice, the free checks are reliable for surface errors. Grammarly catches misplaced commas, subject-verb disagreement, doubled words, and most spelling mistakes faster than a human proofreader running through a document cold. That's genuinely useful. A missed comma after an introductory clause, for instance, is exactly the kind of error that slips past writers who know the rule perfectly well but stop seeing their own text. If you want a refresher on that specific rule, the guide on using commas with introductory clauses and phrases covers it in detail.
The paid checks are more variable. Tone detection works well for obvious cases: Grammarly will flag a sentence that reads as blunt or dismissive in a customer email. It struggles more with subtle register shifts, and it can't tell whether a confident, assertive tone is appropriate for your specific reader or not. Only you know that.
Where Grammarly performs well in business writing
The tool genuinely earns its keep in three areas.
- Wordiness. Grammarly consistently flags phrases like "in order to," "at this point in time," and "due to the fact that." These are the constructions that bloat business prose and slow readers down. The suggested replacements are usually correct.
- Passive voice overuse. The tool marks passive constructions and offers active rewrites. Not every passive sentence needs to go, but Grammarly's flags at least force you to make a conscious choice rather than defaulting to passive out of habit.
- Consistency errors. If you write "on-site" three times and then "onsite" once, Grammarly will catch the inconsistency. That matters more than it sounds in long documents. (For the record, both forms exist; the question of onsite vs on-site comes down to style guide and context.)
Where Grammarly falls short
The weaknesses are real, and business writers should know them before relying on the tool too heavily.
Grammarly can't evaluate whether your word choice fits the audience. It won't tell you that "per our conversation" sounds stiff in a casual client email, or that "as per" sounds bureaucratic anywhere. It checks form, not relationship. A sentence can be grammatically clean and still be the wrong thing to say.
Context blindness is the bigger issue. Grammarly doesn't know whether you're writing to a long-standing client or a new regulator. It can't assess whether your opening paragraph actually answers the reader's most pressing question, or whether your executive summary leads with the right finding. These are the skills that separate good business writing from merely correct business writing, and no automated tool handles them.
The plagiarism checker is also limited for professional use. It's built for academic writing and checks against web content. It won't help you identify whether a passage inadvertently mirrors an internal template you've seen circulated around the office for years.
Free vs Pro: is the upgrade worth it?
For most individual business writers, the free tier covers 80% of what the tool does well. If your main goal is catching typos, grammar slips, and obvious wordiness before you hit send, the free plan does that. The jump to Pro makes more sense if you write long-form content regularly, work across teams where tone consistency matters, or produce documents that go to external audiences and get scrutinised closely.
One practical tip: paste your most critical documents (a proposal, a formal report, a message to a senior stakeholder) into the web editor even on the free plan. The full-document view catches more than the browser extension, which sometimes ignores text in form fields or CMS editors.
How to use Grammarly without letting it flatten your voice
The most common complaint from experienced writers testing Grammarly is that accepting every suggestion produces text that sounds correct but generic. The suggestions are trained on a vast corpus of average prose, and average prose is nobody's goal.
Treat every suggestion as a question, not an instruction. When Grammarly flags a sentence as "unclear," ask yourself whether the sentence is actually unclear or just unusual. If it's genuinely confusing, fix it. If it's a deliberate stylistic choice, dismiss the flag and move on. The tool should sharpen your decisions, not replace them.
The same logic applies to tone suggestions. Grammarly may flag a direct, short sentence as "too blunt" when that directness is exactly what a busy reader needs. Confidence isn't rudeness, and not every softening suggestion improves a message.
The bottom line on testing Grammarly
Grammarly is a competent proofreader and a reasonable first-pass style checker. It won't teach you to write better, but it will stop some of your worst slips from reaching readers. Use it as a final check rather than a writing coach, keep the free tier unless you produce high-volume professional content, and always read the suggestions before accepting them. The tool works best when you're already a careful writer. It doesn't compensate for writers who aren't.