AI grammar checkers have moved beyond simple spell-check. The best ones now analyze tone, suggest rewrites, detect plagiarism, and integrate into your workflow across browsers, editors, and email clients. But the gap between free and paid features is significant, and choosing the wrong tool means either paying for features you do not need or missing errors that matter.

This article compares the four major grammar checking tools based on verified pricing, feature differences, and practical use cases.

Quick Comparison

Tool Free Tier Paid Price Best For
Grammarly Pro Yes (grammar + spelling + 100 AI prompts) $12/mo (annual) / $30/mo All-purpose writing
ProWritingAid Yes (500 word limit) $10/mo (annual) / $399 lifetime Long-form writing, authors
LanguageTool Yes (basic rules) ~$5/mo (annual) Multi-language, privacy
QuillBot Yes (limited paraphrasing) $10/mo (annual) Paraphrasing and rewriting

Grammarly Pro (formerly Premium)

Grammarly is the most widely used grammar checker. In March 2025, Grammarly renamed its Premium plan to Pro (Grammarly Pro page).

Verified pricing:

Plan Annual Billing Monthly Billing
Free $0 $0
Pro $12/user/month $30/user/month
Business $15-25/user/month Quote-based

Free tier covers:

  • Grammar and spelling correction
  • Basic punctuation suggestions
  • 100 monthly AI prompts
  • Browser extension, desktop app, mobile keyboard

Pro adds:

  • Full-sentence rewrites
  • Tone detection and adjustment
  • Clarity and conciseness suggestions
  • Plagiarism detection
  • Advanced style and delivery feedback
  • Up to 149 seats for team use

What Grammarly Pro does well:

  • Catches the widest range of errors across grammar, punctuation, and style
  • Browser extension works in Gmail, Google Docs, Word, social media, and most web text fields
  • Explanations for suggestions help writers learn from corrections
  • Tone detection is useful for professional communication

Known limitations:

  • Pro suggestions can feel prescriptive for writers with an intentional style
  • Occasionally flags correct but uncommon phrasing
  • Can slow down browser performance when checking long documents
  • Plagiarism checker requires Pro plan; free tier does not include it

When Grammarly Pro is worth it: You write professionally (emails, reports, content) and need consistent error checking across all your applications. The $12/month annual price is reasonable for daily use.

ProWritingAid

ProWritingAid targets writers who need deeper analysis than basic grammar checking. It provides 20+ writing analysis reports covering pacing, repetition, readability, dialogue tags, and more.

Verified pricing (ProWritingAid Pricing, SaaS Price Pulse):

Plan Monthly Annual Lifetime
Free $0 $0 —
Premium $30/mo $120/yr ($10/mo) ~$399
Premium Pro — $144/yr ($12/mo) ~$699

The lifetime option is unusual in this market and offers significant savings for long-term users. ProWritingAid confirms that lifetime subscriptions include all future updates.

What ProWritingAid does well:

  • Writing style analysis goes deeper than any competitor
  • Reports on overused words, sentence length variation, readability metrics
  • Integrates with Scrivener, Word, Google Docs, and desktop apps
  • Lifetime plan eliminates recurring subscription cost

Known limitations:

  • Free tier limited to 500 words per check — too restrictive for real use
  • Interface is less polished than Grammarly
  • The number of reports can be overwhelming for casual users
  • Not as seamless in-browser as Grammarly (fewer integrations)

When ProWritingAid is worth it: You write long-form content (books, academic papers, long articles) and benefit from structural analysis beyond grammar. The lifetime plan at $399 is a good deal if you write regularly and want to avoid monthly subscriptions.

LanguageTool

LanguageTool is an open-source grammar checker with strong multilingual support and a self-hosting option.

Key differentiator: Open-source and self-hostable.

LanguageTool can run on your own server with no request limits. However, the self-hosted version only includes free-tier grammar rules — it does not include the premium rules (advanced style and punctuation checks) without a premium license (Stack Overflow discussion).

Verified pricing:

Plan Price
Free (cloud) $0, basic rules
Free (self-hosted) $0, basic rules, unlimited requests
Premium (cloud) ~$5/month (annual billing)
Teams/Business Higher, quote-based

What LanguageTool does well:

  • Supports 30+ languages (best multilingual grammar checker)
  • Open-source code is transparent and auditable
  • Self-hosting option for complete data privacy
  • More affordable than Grammarly for paid features

Known limitations:

  • English grammar checking is less accurate than Grammarly
  • Fewer integrations and smaller extension ecosystem
  • Self-hosted version lacks premium rules without additional licensing
  • Interface is functional but less polished

Self-hosting costs: If you want to self-host LanguageTool with reasonable performance, hosting costs start around $18-33/month for a basic server (Elestio pricing). This is more expensive than the cloud premium plan unless you need the privacy guarantee.

When LanguageTool is worth it: You write in multiple languages, you need data privacy (self-hosting), or you want the most affordable paid grammar checker at ~$5/month.

QuillBot

QuillBot focuses on paraphrasing and rewriting rather than comprehensive grammar checking.

Verified pricing:

Plan Price
Free Limited paraphrasing, basic grammar
Premium $10/month (annual billing)

What QuillBot does well:

  • Paraphrasing with multiple tone modes (Standard, Formal, Creative, Fluency)
  • Useful for breaking writer’s block or finding alternative phrasing
  • Includes a summarizer and citation generator

Known limitations:

  • Paraphrasing can subtly change meaning — always review the output
  • Grammar checking is less comprehensive than Grammarly or ProWritingAid
  • Free tier limits paraphrasing to short passages
  • Not a complete grammar solution on its own

When QuillBot is worth it: You primarily need help rephrasing and rewriting sentences, not comprehensive grammar checking. Pairs well with Grammarly Free for a complete setup.

How to Choose

Your Situation Best Tool Why
Professional writing daily Grammarly Pro Most comprehensive, works everywhere
Writing books or long articles ProWritingAid Premium Deep style analysis, lifetime option
Writing in multiple languages LanguageTool Premium Best multilingual support
Need data privacy LanguageTool (self-hosted) Open-source, runs locally
Budget under $10/month LanguageTool Premium (~$5/mo) Good value for paid features
Need paraphrasing help QuillBot Best rewriting tool
Want free only Grammarly Free + QuillBot Free Covers grammar and basic rewriting

The Practical Stack

For most people: Grammarly Free covers basic grammar and spelling in your browser. Upgrade to Pro ($12/month) when you need tone detection and full-sentence rewrites for professional communication.

For authors: ProWritingAid for structural analysis and style reports. Pair with Grammarly Free for quick in-browser checking.

For privacy-conscious users or multilingual writers: LanguageTool Premium at ~$5/month. Self-host if data cannot leave your infrastructure.

FAQ

Is Grammarly Pro worth $12/month?

If you write professionally (emails, reports, content marketing, client communication), yes. The tone detection, full-sentence rewrites, and plagiarism detection are the features that justify the cost. For casual use, the free tier is sufficient.

Can these tools replace a human editor?

For everyday writing (emails, internal documents, social media), they are sufficient. For published books, legal documents, academic papers, or content where brand voice precision matters, human editing still provides value that AI grammar checkers cannot match.

Is Grammarly safe for confidential documents?

Grammarly processes your text on their servers to provide corrections. Their privacy policy states they do not sell user data, but if you work with highly confidential content (legal, medical, proprietary), consider LanguageTool self-hosted where text never leaves your machine.

Which is more accurate for English writing?

Grammarly consistently catches the most errors and provides the most helpful suggestions for English writing. ProWritingAid is close for grammar but excels in style analysis for long-form content.

Sources

Bottom Line

Grammarly Free for most people (good enough for daily writing). Grammarly Pro if you write professionally. ProWritingAid if you write books or long-form content (the lifetime plan at $399 is a strong value). LanguageTool for multilingual writing or data privacy needs. Do not pay for multiple grammar tools — pick one that matches your writing needs.