Grammarly has spent fifteen years convincing the world that a green underline means safety. The pitch is seductive: write anywhere, click accept, sound competent. But the product that started as a grammar checker has mutated into a generative AI layer that drafts emails, rewrites paragraphs, and nudges your tone toward whatever the model considers "professional." The question isn't whether it catches typos — it does. The question is whether the suggestions make your writing better or just more average.

Three tiers exist now. Free handles spelling, grammar, and basic tone hints. Premium unlocks the full rewrite engine, plagiarism scanning, and Grammarly GO. Business adds style guides, analytics, and a three-seat floor. Each tier integrates everywhere you type: Gmail, LinkedIn, Notion, Google Docs, Twitter, Word, the desktop app. The infrastructure is impressive. The editorial judgment embedded in the model is where the trouble starts.

Grammarly Free — 8.3/10

The free tier earns its keep. It catches subject-verb disagreements, missing articles, comma splices — the mechanical errors that survive a quick proofread. Browser extension coverage is near-total; the underline appears in every web text field without configuration. Microsoft Word and Google Docs add-ons work without friction. You get basic tone detection (confident, friendly, formal) but no rewrites, no plagiarism scan, no generative AI. For a student polishing an essay or a contractor firing off Slack messages, this is sufficient. The engine doesn't nag for upgrades aggressively. It simply stops at the line where style becomes subjective.

Limitations surface fast. No full-sentence rewrites means you fix one error at a time. No clarity suggestions means wordy constructions survive. The tone detector flags "this sounds tentative" but won't rewrite it. If you write in English as a second language, the free tier catches the obvious mistakes but leaves the subtle ones — preposition choice, article usage, idiom interference — untouched. That's the upgrade hook, and it's honest about it.

Grammarly Premium — 8.8/10

At $12 per month billed annually ($144/year), Premium delivers the feature set most buyers imagine when they hear "Grammarly." Full-sentence rewrites compress wordy passages into tighter alternatives. Clarity suggestions flag passive constructions, nominalisations, hedging language. The tone detector expands to eight dimensions — analytical, respectful, enthusiastic, and so on — with a slider that shows how your text registers. Grammarly GO, the generative layer, drafts replies from a prompt ("write a polite decline to this meeting invite"), expands bullet points into paragraphs, shortens rambling sections, and adjusts formality. It works inside the same inline UI: highlight, click, insert.

The plagiarism checker draws from a 16-billion page web index. It catches copied blog posts, Wikipedia lifts, and public-domain text. It does not reach behind paywalls — JSTOR, Elsevier, SpringerLink — so academic writers relying on it for thesis integrity are gambling. For marketing copy, client proposals, and SEO content, it's adequate. The writing goals panel lets you set audience, formality, domain (business, academic, creative), and intent; suggestions shift accordingly. But the homogenisation problem intensifies here. Accept every clarity rewrite and your voice flattens into corporate mid-Atlantic. The model prefers "utilise" over "use" when formality is high, "leverage" when domain is business. It has opinions, and they're not yours.

Grammarly GO is useful for low-stakes drafting — first-pass emails, meeting summaries, LinkedIn comments. It hallucinates facts occasionally, so verify numbers and names. The prompt bar appears beside the score card; you type instructions in natural language. Response latency averages two to three seconds. It's not a replacement for thinking. It's a replacement for the blank page.

Grammarly Business — 8.5/10

Business tier costs $15 per user per month with a three-seat minimum ($540/year baseline). The value proposition: consistency at scale. Style guides let administrators define terminology (product names, capitalisation rules, forbidden words), and the engine flags deviations across the team. Analytics surface team-level metrics — clarity scores, tone distribution, suggestion acceptance rates. Consistency reports highlight which writers drift from the guide. For a fifty-person marketing org shipping daily blog posts, newsletters, and support macros, this prevents the death by a thousand inconsistencies.

The three-seat floor excludes solo founders and micro-agencies. Per-seat pricing scales linearly — no volume discounts until enterprise negotiations. SAML SSO, dedicated support, and custom roles live in the Enterprise tier, which requires a sales call and unlisted pricing. Business inherits all Premium features, so each seat gets Grammarly GO and plagiarism scanning. The admin dashboard is clean but thin; you can't export suggestion logs for compliance audits. If you need that, you're in Enterprise territory.

Verdict

Grammarly Free is the best free proofreader on the market. Full stop. Premium at $144/year is worth it for ESL professionals, high-volume freelancers, and anyone whose revenue depends on error-free client-facing copy. The generative AI saves time on routine drafting. The plagiarism checker is a bonus, not a reason to buy. Native English writers with a developed voice should treat suggestions as signals, not commands — accept the mechanics, reject the style. Business tier pays off when team inconsistency costs more than $540/year; otherwise, share a Premium account and maintain a shared style doc. The product is powerful. The danger is subtle: it makes bad writing competent and good writing generic. Use it to catch what you missed. Don't use it to decide how you sound.

Is Grammarly Premium worth it for students?

Only if you write frequently in English as a second language or submit work where mechanical errors carry penalties. The plagiarism checker misses paywalled journals, so it won't protect against accidental academic citation gaps. Native speakers get diminishing returns beyond the free tier.

Does Grammarly work offline?

The desktop app caches documents for offline editing, but suggestions require an internet connection. Browser extensions and add-ins are fully cloud-dependent. Plan for connectivity if you write on flights.

Can Grammarly replace a human editor?

No. It catches mechanics and suggests clarity improvements. It cannot evaluate argument structure, factual accuracy, narrative pacing, or whether your joke lands. A human editor still earns their fee on the decisions software cannot model.

What happens to my data?

Grammarly processes text on its servers to generate suggestions. The company states it does not sell data or use content for advertising. Enterprise tiers offer data residency options and zero-retention modes. For sensitive legal or medical documents, review the current privacy policy before pasting.