Revise Blog - Building a post-AI word processor
The best AI grammar checkers in 2026
Dedicated checkers and general AI models compared on price, how they check, and what our proofreading benchmark measured
Artur Sapek, Founder of Revise9 min read
“AI grammar checker” now covers two kinds of tool. Classic checkers such as Grammarly and LanguageTool underline mistakes while you write and have added AI rewrites and, in Grammarly’s case, document agents. General AI models, used through ChatGPT, Claude, or an editor built on them, proofread a passage or document when you ask. Below, we compare the other tools against Grammarly.
I have spent the past year building Revise, the word processor with an AI editing agent that appears second on this list, and to choose its models we built ErrataBench, an open proofreading benchmark. We use its numbers below where they apply. The prices come from each vendor’s own pages, which are linked in the sources at the end.
AI grammar checkers at a glance
Table 1 covers price and what each tool’s AI does. Table 2 covers when each one checks and how its fixes appear.
| Tool | Best for | Free plan | Paid from | AI capabilities |
|---|---|---|---|---|
| Grammarly | Real-time checks across desktop, browser, and mobile | Yes (100 AI prompts a month) | $12/mo (Pro) | Grammar, tone, and sentence rewrites as inline suggestions, AI detection |
| Revise | Whole-document AI proofreading you review as tracked changes | Yes (daily AI limit) | $8/mo (Plus) | Agent proposes text and formatting edits as suggestions. Header, footer, and page-layout changes apply directly |
| LanguageTool | Multilingual checking on a budget | Yes (2,000 characters per text field, 3 AI rephrasings a day) | $5.83/mo (Premium) | Grammar, punctuation, and style checks in 30+ languages, AI sentence rephrasing |
| ProWritingAid | In-depth style reports for long-form | Yes (suggestions for 500 words at a time, 10 Rephrases a day) | $10/mo (Premium) | Grammar, style, and line-editing reports, Rephrase, Chapter Critique, paid manuscript analysis |
| ChatGPT | Pasted-text proofreading with OpenAI models | Yes (3 file uploads a day, 27K-token Instant context) | $8/mo (ChatGPT Go) | Writing blocks for revising a draft or selection, reads uploaded DOCX and PDF |
| Claude | Careful proofreading with Anthropic models | Yes (Sonnet and Haiku models, no Claude Docs or Microsoft 365 add-ins) | $20/mo (Claude Pro) | Artifacts and Claude Docs for drafting, reads and creates DOCX and PDF files, Word add-in edits as tracked changes |
| QuillBot | Grammar checks plus paraphrasing | Yes (paraphrases up to 100 words, summaries up to 1,200 words) | $8.33/mo (Premium) | Paraphrasing in multiple modes, grammar checks, summaries, humanizer, AI detection, AI chat |
| Microsoft Editor | Built-in checks in Word, Outlook, and Edge | Yes (basic spelling and grammar) | $9.99/mo (Microsoft 365 Personal) | Spelling and grammar, clarity, conciseness, formality, and vocabulary refinements with Microsoft 365 |
| Tool | When it checks | How fixes appear | Where it works |
|---|---|---|---|
| Grammarly | As you type, plus a whole-document review when you ask | Underlines you accept one by one, or comments from the document agent | Browsers, desktop, mobile, Word, Google Docs |
| Revise | When you ask, across the whole document | Tracked changes you accept or reject | Its own browser editor, imports and exports .docx |
| LanguageTool | As you type | Inline suggestions | Browsers, desktop, iOS, Word, Google Docs |
| ProWritingAid | As you type, plus reports | Inline suggestions and reports | Web, desktop, browsers, Word for Windows, Google Docs |
| ChatGPT | When you ask | A corrected reply, or inline suggestions in Canvas | Web, desktop, mobile, Word add-in |
| Claude | When you ask | A corrected reply or a new file, Word tracked changes via Claude for Word | Web, desktop, mobile, Word add-in (Pro and up) |
| QuillBot | On text in its tools | Suggestions and rewritten text in its tools | Web, browsers, Mac, mobile, Word add-in |
| Microsoft Editor | As you type | Inline suggestions | Word and Outlook, Edge has built-in proofing |
To see AI proofreading as tracked changes, paste your text or import a .docx below and ask for a proofread. It opens in Revise in your browser. You can make one request without an account, and you need a free account to accept changes.
How we evaluated them
We use Grammarly as the baseline. It checks your writing as you type in Word, Google Docs, browsers, and its desktop and mobile apps, and the Pro plan adds AI rewrites and AI-text detection. We compared each tool on the six questions below. We did not run a controlled test of these apps, so the only accuracy numbers in this post come from a benchmark of AI models, and they are labeled that way.
- Is there a public, reproducible accuracy result for the specific model doing the checking?
- Does it check as you type, or only when you ask?
- Does it check a sentence, a text field, or the whole document?
- Can you accept or reject each correction?
- What does the free plan cover, and where are its limits?
- Does it work in browsers, Word, and Google Docs, or only in its own app?
ErrataBench seeds 99,000 words of literature, legal writing, and technical manuals with realistic errors, then gives every model the same prompt, text chunks, and find-and-replace tools. It tests models in that harness, not the ChatGPT or Claude apps, and not drafting quality (full results and method). Table 3 lists its top results.
| Model | Maker | Reasoning | Fix rate |
|---|---|---|---|
| GPT-5.6 Sol | OpenAI | Medium | 96.5% |
| GPT-6 Astra | OpenAI | Low | 96.1% |
| Claude Opus 5 | Anthropic | Low | 95.7% |
| GPT-6 Sol | OpenAI | None | 95.4% |
| GPT-5.5 | OpenAI | High | 94.8% |
| Claude Opus 5.5 | Anthropic | High | 94.7% |
| GPT-6 Luna | OpenAI | - | 90.9% |
Where this post refers to our own test, it means our AI document review test, which ran several of these tools on the same contract in August 2026.
The 8 best AI grammar checkers
1. Grammarly: Best for checking as you type
- Free plan: Yes, 100 AI prompts/mo
- Paid from: $12/mo
- Built-in AI: Grammarly AI
Grammarly underlines mistakes as you write in Word, Google Docs, email clients, and websites, through desktop apps for Windows and Mac, browser extensions, and mobile apps. Spelling and basic grammar corrections are free in 23 languages, and advanced suggestions cover six.
The free plan includes 100 AI prompts a month. Pro ($12 a month billed annually, $30 month to month) adds full-sentence rewrites, tone adjustments, plagiarism and AI-text detection, and 2,000 prompts. Grammarly does not publish which models it uses or reproducible accuracy figures. In our document review test, its document agent reviewed the whole document but left comments rather than proposed edits.
Pick it if you want corrections across the apps you type in. Skip it if you need proposed document edits as individually reviewable tracked changes.
2. Revise: Best for proofreading a whole document
- Free plan: Yes, daily AI limit
- Paid from: $8/mo
- Built-in AI: Revise Agent
Revise is a browser word processor whose AI agent proofreads the whole document when you ask and shows its text and formatting fixes as tracked changes to accept or reject. It does not check as you type. You can choose GPT, Claude, Gemini, or Grok models.
The Free plan runs GPT-6 Luna under a daily AI limit, and GPT-6 Sol, GPT-6 Astra, and Claude Opus 5.5 need Pro ($20 a month). It is a separate editor, not a Word add-in. It imports and exports .docx, and unresolved fixes export as Word tracked changes.
Pick it if you proofread reports, papers, or contracts before they go out. Skip it if you want checks inside Word, email, and other apps as you type.
3. LanguageTool: Best for multilingual writing
- Free plan: Yes, 2,000 characters
- Paid from: $5.83/mo
- Built-in AI: LanguageTool
LanguageTool checks grammar, punctuation, and style in more than 30 languages, as you type in browsers, Word, Google Docs, and its Mac and Windows apps. Its core is open source (LGPL), and it offers a proofreading API.
Free covers 2,000 characters per text field with three AI rephrasings a day. Premium is $5.83 a month billed annually, with 150,000 characters and unlimited rephrasing.
Pick it if you write in several languages or want a low annual subscription price. Skip it if you want AI to revise whole documents.
4. ProWritingAid: Best for style depth
- Free plan: Yes, 500 words at a time
- Paid from: $10/mo
- Built-in AI: ProWritingAid
ProWritingAid combines grammar checking with more than 25 reports and AI features such as Rephrase and Chapter Critique. It is aimed at fiction writers, checks English only, and works in Word for Windows, Google Docs, Scrivener, and major browsers.
Premium is $10 a month billed yearly or $30 month to month, and a $399 lifetime license is available.
Pick it if you want detailed feedback on long manuscripts. Skip it if you write in other languages.
5. ChatGPT: Best for pasted text with OpenAI models
- Free plan: Yes, 3 uploads/day
- Paid from: $8/mo
- Built-in AI: ChatGPT
ChatGPT proofreads text you paste or upload, and Canvas can show inline suggestions. OpenAI models hold four of the top six ErrataBench places, and GPT-5.6 Sol with medium reasoning had the highest fix rate, 96.5%. ChatGPT’s pricing page lists GPT-6 and GPT-5.6 models across its plans, but the model that answers depends on your plan and settings.
Free allows three file uploads a day. Go is $8 a month and Plus is $20. The ChatGPT for Word add-in is available on every plan, subject to plan limits.
Pick it if you want a strong second pass on important text. Skip it if you want fixes marked as tracked changes in your file. In our document review test, ChatGPT returned a new .docx without them.
6. Claude: Best for cautious proofreading
- Free plan: Yes, Sonnet and Haiku
- Paid from: $20/mo
- Built-in AI: Claude
Claude proofreads pasted or uploaded text and can return a .docx on every plan. On ErrataBench, Claude Opus 5 fixed 95.7% of errors, and Claude Opus 5.5 had the lowest bad-fix rate (0.4%) of any model above 90%, while leaving 4.9% of errors untouched.
Free includes Sonnet and Haiku models. Opus models and the Claude for Word add-in need Pro, at $20 a month or $17 billed annually. Claude for Word applies edits as native Word tracked changes when Track Changes is on, and Claude produced tracked changes in our document review test.
Pick it if a wrong correction costs you more than a missed one. Skip it if you want Opus-level proofreading for free.
7. QuillBot: Best with a paraphraser
- Free plan: Yes, 100-word paraphrases
- Paid from: $8.33/mo
- Built-in AI: QuillBot
QuillBot bundles a grammar checker (6 languages) with a paraphraser (23 languages), summarizer, and AI detector, on the web, in a Word add-in, in Chrome and Edge, and on mobile. Premium is $8.33 a month billed annually or $19.95 month to month.
Pick it if you often reword as well as correct. Skip it if you do not need the paraphrasing and summarizing bundle.
8. Microsoft Editor: Best inside Word
- Free plan: Yes, basic checks
- Paid from: $9.99/mo
- Built-in AI: Microsoft Editor
Microsoft Editor is built into Word and Outlook. Basic spelling and grammar are free, and Microsoft 365 adds clarity, conciseness, and formality refinements. Its browser extensions were retired on October 31, 2025.
Pick it if you already pay for Microsoft 365. Skip it if you need the same checker in non-Microsoft apps and on mobile.
Also considered: Wordtune (rewrite suggestions with free spelling and grammar checks) and Hemingway Editor (readability highlights, with grammar and AI fixes on Plus). Both focus on style more than grammar.
Which checker fits your writing?
Some people use two tools, one that checks while they draft and one for a final pass on the finished piece. Table 4 matches common jobs with a tool.
| The job | Best fit | When Grammarly still wins |
|---|---|---|
| Fix mistakes in email and chat as you type | Grammarly | Grammarly is the fit here. |
| Proofread a finished report or paper, with fixes as reviewable tracked changes | Revise, or Claude for Word on Claude Pro | You want checks as you type in email and web apps. |
| Check writing in several languages | LanguageTool | You need advanced suggestions in one of Grammarly's six advanced languages. |
| Edit a novel manuscript | ProWritingAid | You want real-time checks across email and the web rather than manuscript reports. |
| Double-check a paragraph you already wrote | ChatGPT or Claude | You want suggestions automatically while you type. |
What Grammarly still does best
- It runs in more places, with desktop apps for Windows and Mac, extensions for Chrome, Safari, Firefox, and Edge, and apps for iPhone, iPad, and Android.
- Spelling and basic grammar corrections are free in all 23 of its supported languages.
- Pro includes plagiarism and AI-text detection along with 2,000 AI prompts a month.
How to switch from Grammarly
- Turn off the Grammarly extension or desktop app before installing another real-time checker, so two tools are not marking up the same text.
- Run one representative draft through the new tool and compare what it flags with what Grammarly flagged.
- Add names and jargon from your Grammarly dictionary to the new tool.
- Cancel the old paid plan only after the new one fits.
What AI grammar checkers still miss
Across every model on ErrataBench, spelling and word-form errors were resolved about 92% of the time, and meaning, flow, and style errors only about 81%. Some of the fixes are also wrong. For example, GPT-5.6 Sol made bad fixes on 1.2% of errors. Review corrections before you accept them, especially in legal or technical text.
What each checker costs
| Tool | Cheapest paid plan | Monthly | Per year | AI on that plan |
|---|---|---|---|---|
| Grammarly | Pro (billed annually, $30 month to month) | $12/mo | $144 | 2,000 AI prompts a month |
| Revise | Plus (or $72/yr billed annually) | $8/mo | $72 | Monthly AI limit, no daily limit. GPT-6 Sol, GPT-6 Astra, and Claude Opus 5.5 need Pro |
| LanguageTool | Premium (billed annually ($69.90), $24.90 month to month, $4.99/mo on a 2-year plan) | $5.83/mo | $69.90 | Unlimited AI rephrasing, 150,000 characters per text field, personal style guide |
| ProWritingAid | Premium (billed yearly ($120), $30 month to month) | $10/mo | $120 | Unlimited Rephrases, 1 Chapter Critique and 5 Sparks a day |
| ChatGPT | ChatGPT Go (monthly billing, may include ads) | $8/mo | $96 | More messages, uploads, and memory than Free |
| Claude | Claude Pro (or $17/mo billed annually) | $20/mo | $200 | More usage, Opus models, Claude Docs (beta), and Claude in Microsoft 365 |
| QuillBot | Premium (billed annually ($99.95), $19.95 month to month) | $8.33/mo | $99.95 | Unlimited paraphrasing, 6,000-word summaries, higher AI chat usage |
| Microsoft Editor | Microsoft 365 Personal (or $99.99 a year) | $9.99/mo | $99.99 | Advanced grammar and style refinements, Copilot in Word is also included |
The bottom line
The main question is whether you want checks while you type or when you ask. For checks while you type, use Grammarly, or LanguageTool if you want more languages at a lower price. For a pass over a finished document, several GPT and Claude configurations fixed more than 95% of seeded errors on ErrataBench, although that benchmark does not compare the apps above. If you want the fixes as tracked changes, Revise does that in its own browser editor, and Claude for Word does it inside Word on Claude Pro when Track Changes is on.
Sources
Prices and plan details were checked against each vendor’s own pages on October 4, 2026. Prices are in US dollars as each vendor lists them, and some include local tax. Vendors change plans often, so confirm on the linked page before you buy.
- Grammarly: Usage and document limits, Languages, Desktop app, Browser extension, Grammarly Docs, Plans, Grammarly for Word
- Revise: Pricing, Supported models, Agent capabilities, Word compatibility, Import and export, MCP server, Suggesting mode, AI usage limits
- LanguageTool: Premium, LanguageTool for Word, Core source code (LGPL)
- ProWritingAid: Pricing, System requirements, Word for the web, Home page
- ChatGPT: Pricing, Free tier FAQ, File uploads FAQ, Writing blocks, ChatGPT for Word, Capabilities overview, ChatGPT for Word, Creating documents with ChatGPT Work, Google Drive app, Google app data controls, Supported file types, ChatGPT for Google Sheets
- Claude: Pricing, Upload files, Create and edit files, Claude Docs, Claude for Word, Custom connectors
- QuillBot: Premium plans, How much is QuillBot Premium?
- Microsoft Editor: Microsoft Editor overview, Browser extension retirement, Compare Microsoft 365 plans
