Grammarly vs ProWritingAid vs LanguageTool 2025: Best AI Grammar Checker

Every writer needs a grammar checker, but not all grammar checkers are created equal. Grammarly, ProWritingAid, and LanguageTool each claim to be the best — and each genuinely excels in different areas.

I tested all three on the same documents over 30 days across multiple contexts: academic writing, blog posts, business emails, and creative fiction. Here’s the honest breakdown.

Side-by-Side Comparison

Accuracy Testing: Grammar Detection

I ran 50 intentionally incorrect sentences through each tool covering: grammar errors, punctuation mistakes, commonly confused words (affect/effect, their/they’re), awkward phrasing, passive voice overuse, and readability issues.

Results

• Grammarly: Caught 46/50 errors. Missed 2 subtle subject-verb agreement issues and 2 complex punctuation cases. Best at explaining why something is wrong.
• ProWritingAid: Caught 44/50. Missed similar errors but provided more detailed style analysis. Flagged more false positives (9 vs. Grammarly’s 4).
• LanguageTool: Caught 38/50 for English. Significantly better for non-English errors. More conservative about style suggestions.

All three tools dramatically outperform built-in word processor spell-checkers, which typically catch 20-25 of the same 50 errors.

Grammarly: Deep Dive

What Makes Grammarly Stand Out

Grammarly’s competitive advantage is its real-time, context-aware suggestions across virtually every platform. The browser extension works in Gmail, LinkedIn, Twitter, Notion, WordPress — essentially anywhere you type online.

Grammarly Pricing (2025)

• Free: Basic grammar and spelling, limited style suggestions
• Premium: $12/mo (annual) — Full grammar, clarity, engagement, delivery suggestions
• Business: $15/mo/member (min 3) — Team goals, analytics, brand voice, SAML SSO

Standout Features

• Grammarly Go: Generative AI writing assistance integrated with suggestions
• Tone detector: Analyzes and helps adjust tone for audience
• Plagiarism checker: Included in Premium (checks against 16B web pages)
• Writing goals: Adjust suggestions based on audience, formality, domain
• Brand tone (Business): Enforce consistent voice across team communications

Grammarly Pros & Cons

• Pro: Best-in-class browser extension coverage
• Pro: Easiest to use — minimal learning curve
• Pro: Includes plagiarism checker at no extra cost
• Con: English only (major limitation for multilingual writers)
• Con: Pricier than alternatives for comparable features
• Con: Privacy-conscious users note extensive data collection

ProWritingAid: Deep Dive

What Makes ProWritingAid Stand Out

ProWritingAid’s defining feature is its in-depth writing reports. While Grammarly gives you sentence-level suggestions, ProWritingAid gives you document-level analysis: pacing reports, dialogue analysis, grammar patterns to work on, readability by paragraph, and more.

ProWritingAid Pricing (2025)

• Free: 500 words per check, limited report types
• Premium: $10/mo (annual) — Full analysis, unlimited words
• Premium+: $12/mo (annual) — Adds plagiarism checker
• Lifetime: $399 one-time — Premium features forever (best long-term value)

Standout Features

• 20+ writing reports: Overused words, sentence length variation, pacing, grammar patterns, dialogue tags, sensory details, and more
• Genre-specific analysis: Different benchmarks for literary fiction vs. thriller vs. romance
• Readability score: Multiple metrics (Flesch-Kincaid, Gunning Fog, etc.)
• Integration with Scrivener: The only tool in this comparison with native Scrivener support
• Writing style guide: Create personal style rules the tool enforces

ProWritingAid Pros & Cons

• Pro: Most depth for self-editing and craft improvement
• Pro: Scrivener integration (unique)
• Pro: Lifetime license option for long-term writers
• Con: Steeper learning curve — overwhelming for simple use cases
• Con: Google Docs integration is limited compared to competitors
• Con: English only, like Grammarly

LanguageTool: Deep Dive

What Makes LanguageTool Stand Out

LanguageTool is the only major grammar checker that is open source, supports 30+ languages, and can be self-hosted for complete privacy. It’s the natural choice for non-English writers and privacy-conscious users.

LanguageTool Pricing (2025)

• Free: 20,000 characters/check, basic suggestions, browser extension
• Premium: $5.83/mo (annual) — Unlimited text, advanced grammar, picky mode
• Teams: $4.99/mo/user (annual, min 5 users) — Shared style guide, team management

Standout Features

• 30+ languages: German, French, Spanish, Portuguese, Dutch, Polish, and more — actually good, not token support
• Self-hosting: Run LanguageTool on your own server for complete data privacy
• Picky mode: Premium feature that catches subtle style issues most tools miss
• Open source core: Community-contributed rules, transparent operation
• LibreOffice integration: Native integration for open source office users

LanguageTool Pros & Cons

• Pro: Only tool supporting 30+ languages properly
• Pro: Self-hosting available for legal/medical/confidential writing
• Pro: Most affordable premium tier
• Pro: No AI data training concerns with self-hosted version
• Con: Less accurate for English than Grammarly/ProWritingAid
• Con: No plagiarism checker
• Con: No desktop app (browser extension + web editor only)

Academic Use Comparison

For students and academics, grammar checkers have specific requirements: no plagiarism risk, academic tone support, and citation-safe operation.

Academic recommendation: Grammarly Premium for most students (plagiarism + grammar + ease); LanguageTool self-hosted for highly sensitive research documents.

Browser Extension Comparison

The browser extension is often the primary way writers interact with these tools. I tested all three across Chrome, Firefox, and Edge on Gmail, Google Docs, Notion, and LinkedIn.

• Grammarly: Works flawlessly on all tested platforms. Real-time suggestions appear inline. Minor performance impact on complex pages. No issues detected across 30 days.
• ProWritingAid: Works well in most contexts but occasionally fails to load on dynamic pages. Better suited for dedicated writing sessions than casual use.
• LanguageTool: Solid coverage, slightly less seamless inline experience than Grammarly. Works in more niche contexts due to open source architecture.

Who Should Use Each Tool?

Choose Grammarly if:

• You write across multiple platforms (email, social, docs, CMS)
• You need a plagiarism checker included
• Quick, frictionless feedback matters more than deep analysis
• You’re managing a team’s writing quality (Business tier)

Choose ProWritingAid if:

• You’re writing a novel, memoir, or long-form content
• You use Scrivener
• You want to improve your writing craft over time, not just fix immediate errors
• You’re willing to invest time in learning the tool’s reports

Choose LanguageTool if:

• You write in a language other than English
• Privacy and data security are primary concerns
• You’re budget-constrained (cheapest premium, generous free tier)
• You need an open source solution you can self-host

Frequently Asked Questions

Final Verdict

The best AI grammar checker depends on your writing context:

• Everyday writers and professionals: Grammarly Premium
• Authors and serious self-editors: ProWritingAid (consider the Lifetime license)
• Non-English writers and privacy-conscious users: LanguageTool
• Students on a budget: LanguageTool free or ProWritingAid free

None of these tools replace a human editor for high-stakes writing, but all dramatically reduce the time spent on mechanical errors — leaving more cognitive bandwidth for what actually matters: your ideas.