What Grammarly Actually Does

Grammarly was founded in 2009 — ancient history in AI terms — and has spent 17 years building the most comprehensive writing assistance platform available. It’s used by over 30 million people daily across 500,000+ applications and websites.

The core product is deceptively simple: it checks your writing in real time, everywhere you type. But underneath is a sophisticated AI system that analyzes:

• Correctness — grammar, spelling, punctuation (the table stakes)
• Clarity — wordiness, passive voice, unclear antecedents, confusing sentence structure
• Engagement — monotonous sentence patterns, weak word choices, repetitive phrasing
• Delivery — tone detection (confident, friendly, formal, etc.), audience-appropriate language
• Plagiarism — checks against 16 billion web pages and academic databases (Premium)

In 2023, Grammarly added GrammarlyGO — generative AI features including rewrite-in-tone, text generation from prompts, idea brainstorming, and smart replies. These features bring Grammarly closer to ChatGPT’s territory, but they’re designed to complement the editing workflow, not replace a general-purpose AI assistant.

Grammarly Scorecard 📊

4 Real-World Tests 🔬

Test 1: Grammar and Spelling Accuracy

Test: A 2,000-word document with 50 intentionally planted errors — 25 grammar (subject-verb agreement, comma splices, dangling modifiers, etc.), 15 spelling (including homophone errors like “their/there”), and 10 punctuation errors.

Grammarly Premium: Caught 47 of 50 errors (94% detection rate). Missed: one subtle comma splice in a complex sentence, one homophone in a quoted passage, and one dangling modifier that was grammatically ambiguous. False positives: flagged 2 correct sentences as potentially unclear (acceptable — the suggestions were optional). The explanations for each error were clear and educational.

ChatGPT (for comparison): Caught 38 of 50 errors (76%). Struggled with homophone detection (missed “affect/effect” and “complement/compliment”) and was inconsistent on punctuation errors.

Test 2: Tone and Clarity Suggestions

Task: A business email draft that reads as passive-aggressive (“As I mentioned in my previous email… I’m not sure if you had a chance to review…”). Goal: make it sound helpful and collaborative.

Grammarly Premium: Detected the tone as “disapproving” and “accusatory.” Suggested specific rewrites: “As I mentioned” → “Following up on,” “I’m not sure if you had a chance” → “When you have a moment.” The tone shifted from passive-aggressive to collaborative without changing the factual content. Also flagged a clarity issue: a 32-word sentence was suggested to be broken into two sentences for readability.

ChatGPT: Also successfully rewrote the email to be more collaborative. The rewrite was good — arguably more naturally phrased than Grammarly’s suggestions. But ChatGPT required copy-paste → prompt → copy-paste back, while Grammarly worked inline in the email composer.

Test 3: GrammarlyGO Generative Features

Task: Use GrammarlyGO to: (a) generate a 200-word product announcement from bullet points, (b) rewrite a paragraph in three different tones, (c) brainstorm 10 blog post titles on a given topic.

GrammarlyGO: (a) Generated a competent product announcement — clear, professional, accurate to the bullet points. Quality was similar to ChatGPT’s output but slightly more formulaic. (b) Tone rewriting was strong — the “professional,” “friendly,” and “persuasive” versions were distinct and appropriate. This is GrammarlyGO’s best feature. (c) Title brainstorming was competent — 10 titles, some creative, some generic. Comparable to ChatGPT.

Overall: GrammarlyGO is a solid v2 generative AI feature. It’s useful when you’re already editing in Grammarly and want to quickly rewrite or generate without switching tools. But for standalone generative AI work, ChatGPT and Claude are more capable.

Test 4: Cross-Platform Integration

Test: Write and edit across Google Docs (article draft), Gmail (pitch email), Slack (team message), LinkedIn (post), and a web form (contact page). Track whether Grammarly consistently catches errors.

Grammarly Premium: Worked seamlessly across all five platforms. Browser extension caught errors in Gmail, Slack (web), and LinkedIn. Google Docs integration caught errors with inline suggestions. Web form text fields showed Grammarly’s floating widget. No copy-paste required on any platform. This is Grammarly’s killer feature: it’s the AI editor you never have to think about switching on.

ChatGPT/Claude: Require copy-pasting text into a separate tab for each check. Functionally equivalent quality; dramatically more friction.

Pricing

Value assessment: Premium at $12/month is reasonable for professional writers — catching embarrassing errors in client emails and public posts pays for itself quickly. Free tier is generous for casual use, covering basic correctness. Business at $15/user/month is good value for teams that want consistent brand voice across all written communication.

Pros & Cons

Final Recommendation

Last updated: June 30, 2026. Grammarly features and pricing verified against official sources.