writing

Best AI Grammar Checkers

The best AI grammar checkers in September 2026, ranked on real-time sentence-level correction rather than document editing — Grammarly, LanguageTool, Harper, ProWritingAid, QuillBot, Sapling, Ginger, Antidote, Wordtune and the checkers now built into Chrome, Windows, macOS and Android — with verified pricing, language coverage, free-tier caps and what each one sends to a server.

Updated September 2026

Quick answer: For most people in September 2026 the best AI grammar checker is Grammarly’s free tier, because grammar, spelling, punctuation and tone detection are all free, with the same document limits as the paid plan, and it runs in more places than anything else in the category — paying $12 a month buys rewriting and tone control, not better error detection. If you write in more than one language, use LanguageTool, which covers more than 30 languages against Grammarly’s English-only correction. If you do not want your text leaving your machine, use Harper, an Apache-2.0 checker from Automattic that runs entirely on-device in under 10 milliseconds and costs nothing.

The caveat that applies to every tool on this page: no grammar-checking vendor publishes precision or recall figures for its live checker, and no independent 2026 test of these products exists. Every “tested and ranked” grammar-checker comparison currently returned by search runs its own scoring on its own error set, usually alongside affiliate links. The evidence we can stand behind is set out below, including where it runs out.

Prices were verified on vendor pages on 7 September 2026. Three vendors were running promotions on that date, so list and promotional prices are shown separately.

What this page ranks, and what it does not

“Grammar checker” and “proofreader” get used interchangeably and are not the same product.

A grammar checker is corrective and sentence-level. It watches the sentence you are typing and flags what is wrong with it — a subject-verb disagreement, a missing comma, a misspelling, a dangling modifier. It runs continuously, in the app you are already in, and it is judged on how fast it responds, how often it is wrong, how many languages it handles and how many places it works. That is what this page ranks.

A proofreader is corrective and document-level. It takes a finished draft and checks it against itself — an acronym defined twice, hyphenation that drifts between chapters, a citation style applied unevenly — and, for the tools built for it, returns a Word file with every edit as a tracked change. Those tools are ranked on our best AI proofreaders page, and where a vendor appears on both pages the commentary is split by scope rather than repeated.

A writing assistant produces new text. Claude, ChatGPT and the drafting platforms are ranked in best AI for writing.

Here is the split, applied to the vendors that appear in both places.

Four well-known tools are deliberately not ranked here because they are not real-time checkers. Hemingway scores readability and does not check grammar as you type. PerfectIt does document consistency and no grammar correction at all. Scribbr’s AI Proofreader and Writefull Revise are upload-and-return manuscript tools. All four are covered on best AI proofreaders instead.

How good are AI grammar checkers in September 2026?

Short version: near-perfect on spelling, competent on mechanical grammar, weak on structure and meaning, and deliberately quiet.

They are tuned to stay silent, and that is the correct trade

Automated correction is measured as grammatical error correction (GEC), and the field’s standard metric is F0.5, which weights precision twice as heavily as recall (Ng et al., 2014). The assumption behind that weighting is the one that governs how every product on this page behaves: wrongly underlining correct text costs a writer more than silently missing an error. A checker that flagged everything would score badly no matter how many real mistakes it caught.

This is why real-time checkers feel conservative. The only independent measurement of a commercial checker on a public benchmark found Grammarly at 67.3% precision and 51.1% recall on 100 CoNLL-2014 sentences (Wu et al., 2023) — accurate when it speaks, and silent about roughly half the errors in front of it. In the same study’s human audit of 20 corrected sentences, Grammarly produced 14 under-corrections, zero mis-corrections and one over-correction, against 30 over-corrections from ChatGPT.

The ceiling is higher than any product ships

The best published GEC systems reach 72.8 F0.5 on CoNLL-2014 and 81.4 on BEA-2019 (Omelianchuk et al., 2024). Those are research ensembles, not products you can install. No vendor on this page claims a benchmark score at all, which means the gap between what the field can do and what your underline is doing is unmeasured.

Where the tools are strong and where they collapse

The last multi-tool academic comparison remains the clearest picture of the shape, even though it predates large language models: the best performer scored 44.4% overall accuracy and 99% on spelling, while no tool exceeded 11% on sentence-structure errors and none exceeded 25% on semantic errors (Sahu et al., 2020). A 2026 study of a fine-tuned model found the same lopsidedness in modern systems: a 96% correction rate on spelling against false insertion rates above 50% for adjectives and adverbs (Labib et al., AIED 2026).

Practical reading: trust the red underline on a misspelling. Treat a suggestion about sentence structure as an opinion. Nothing on this page reliably catches a sentence that is grammatical and wrong.

Independent testing of these products does not exist

This is worth stating plainly, because the rest of this category will not.

• Every grammar-checker ranking currently on the first page of search results uses the reviewer’s own error set, scored by the reviewer, and most carry affiliate links. Figures such as “20/20 on grammar detection” or “catches 90% of errors” trace to those pages, not to any published methodology.
• Grammarly is the only tool here with an independent benchmark number at all, and it is from a 100-sentence sample in 2023.
• For LanguageTool, ProWritingAid, QuillBot, Sapling, Ginger, Harper, Antidote, Wordtune, Microsoft Editor, Apple’s Writing Tools and Gboard, independent quantitative accuracy testing is data not available.
• Vendor-run comparisons should be read as marketing. CleverType’s published figures putting its own keyboard at 99.4% against Gboard’s 96.1% are a vendor benchmarking itself against a competitor, on an unpublished test set.
• A systematic review of 24 studies of Grammarly in second-language writing found that more than half of them (15) reported problems with its feedback (Dizon and Gayed, 2024) — and Grammarly is the best-evidenced tool in the category.

Our ranking below is therefore built on what can be verified: price, language coverage, where the tool runs, what it sends to a server, and what the vendor documents. It is not built on accuracy claims, because there are none worth using.

Best AI grammar checkers in 2026: the ranking

Ranked on real-time correction quality, verified price transparency, language coverage and reach. Prices confirmed 7 September 2026.

1. Grammarly — best for most writers

Price: Free tier; Pro $12/month billed annually ($144/year) or $30/month billed monthly (Grammarly, support); Enterprise by quote Free tier: grammar, spelling, punctuation and tone detection, plus 100 AI prompts per month. Document limits are the same on Free and Pro: 100,000 characters per upload to the Editor, 50,000 words in any 24 hours and 150,000 words in any 30 days (Grammarly support) Pro adds: full-sentence rewrites, tone adjustment, fluency suggestions, inclusive language, and 2,000 AI prompts per member per month Runs in: Chrome, Safari, Firefox and Edge extensions; Windows and macOS apps; Microsoft Office; Google Docs; iOS and Android keyboards

Grammarly wins this page on a point that most comparisons get backwards: the part of Grammarly that checks your grammar is free. The paid tier sells rewriting, tone and generative prompts. If your problem is that you make typing errors and want them caught everywhere you type, the free tier is the product, and $144 a year buys you a different product.

Its reach is the real moat. No other tool here corrects you in a browser, a desktop app, Office, Google Docs and a phone keyboard from one account.

Why it ranks first: the widest surface area in the category, the only independently measured error-detection score in the category, and a free tier whose document limits are the same as Pro’s.

Limitations for real-time use: correction is English-only, which is disqualifying for bilingual writers. Everything runs in the cloud — your text is transmitted to be checked, with no on-device mode at any price. And the free tier’s 100 monthly AI prompts run out quickly if you use the rewrite suggestions rather than just the underlines.

Note that Grammarly’s parent company renamed itself Superhuman on 29 October 2025 (announcement). The product is still Grammarly and grammarly.com still sells it.

Best for: anyone who wants one checker that follows them into every app and does not want to pay for that.

2. LanguageTool — best for writing in more than one language

Price (EUR, inclusive of VAT): €19.90/month; €39.90/quarter (€13.30/month); €59.89/year (€4.90/month); €99.90 for two years (€4.16/month). Teams €56.90 per user per year up to 20 users (LanguageTool help centre). A promotion was running on 7 September 2026 on top of these figures Free tier: 2,000 characters per text field, three AI rephrasings per day, limited Picky Mode Premium: 150,000 characters per text field and more than 20,000 additional checks across seven languages Runs in: Chrome, Edge, Firefox, Safari, Opera; Google Docs, Word, Apple Pages, LibreOffice; Gmail, Outlook, Apple Mail, Thunderbird; macOS and Windows apps; iOS only, no Android

LanguageTool is the only serious answer if you switch languages during the day. It corrects in more than 30 languages with dialect-specific rules across six English variants, where Grammarly and ProWritingAid correct in English alone.

The second thing it has that nothing else at this price does: the core rule engine is open source (GitHub), and you can run the whole server yourself in Docker. Self-hosting gives you unlimited checking with no character cap and no text leaving your network, which is why it is the standard choice inside companies that will not send drafts to a third party.

One change matters more here than anywhere else on this page: the browser extension now requires Premium (help centre). For a real-time checker that is close to fatal at the free tier, because the extension is the real-time product — without it you are pasting text into a web page, which is not checking as you type at all.

Limitations: the free tier’s 2,000-character cap is applied per text field, which is tight for anything longer than an email. No Android app, so half of mobile is uncovered. LanguageTool publishes no USD price, so a US buyer’s cost depends on card conversion and VAT treatment. Its own pages disagree on the Premium character limit, quoting both 150,000 and 100,000.

Best for: anyone writing in English plus German, French, Spanish, Dutch, Polish or Portuguese, and anyone who needs to self-host.

3. Harper — best for privacy, developers and offline work

Price: free, permanently, under the Apache-2.0 licence. No account, no card, no paid tier (Harper, GitHub) Runs in: VS Code, Neovim, Obsidian and Zed as official editor extensions; browser extensions; plus a language server, a JavaScript library and a Rust crate for building it into your own software Languages: English, in British, American, Canadian, Australian and Indian variants

Harper is the most interesting thing to happen to this category in years, and it is the only entry here that does not want your money or your text. Written in Rust by Elijah Potter and now developed at Automattic, it runs entirely on your device: no network requests, no cloud processing, nothing transmitted. It returns suggestions in under 10 milliseconds.

Because it ships as a language server, it plugs into any editor that speaks LSP, which makes it the obvious pick for anyone writing prose inside a code editor — documentation, commit messages, technical writing, notes in Obsidian.

Limitations: English only, and the scope is narrower than the commercial tools — capitalisation, spelling, awkward phrasing and broken grammar, rather than tone, clarity rewriting or style-guide enforcement. There is no Word add-in, no Google Docs integration and no mobile app. It is a checker for people who write in editors, not a replacement for Grammarly in Gmail.

Best for: developers, privacy-conscious writers, anyone under a policy that forbids sending text to a third-party service, and anyone who wants a good checker for nothing.

4. Microsoft Editor — best for people who live in Word and Outlook

Price: free tier with any Microsoft account; full features with Microsoft 365 Personal at $9.99/month or $99.99/year (Microsoft) Free tier: spelling and basic grammar Paid adds: clarity, conciseness, formality and punctuation-convention suggestions Runs in: Word, Outlook and Word for the web natively. The standalone browser extension was retired on 31 October 2025 (Microsoft)

If you already pay for Microsoft 365, you already own a competent real-time checker, and a large number of people buying Grammarly do not know it. Editor’s underlines are built into Word and Outlook, which is where most business writing actually happens.

Two changes matter this year. First, Word’s Similarity Checker is being retired on 3 October 2026 and removed from Editor (Microsoft 365 message centre MC1466753; reported by The Register, 4 September 2026). Microsoft states that other writing, editing and citation capabilities are unaffected, so the grammar checking stays. Second, Microsoft 365 Copilot in Word for the web can now apply every grammar and spelling correction in one action (Microsoft 365 Insider blog), which is the fastest route from a messy draft to a clean one inside Office.

Limitations: outside Microsoft’s own apps, Editor no longer follows you anywhere — the extension retirement means there is no Editor in Gmail, in a CMS or in a browser text box. Microsoft’s Editor marketing page still lists a browser extension in the free-tier column; it is out of date. Editor also has no on-device mode.

Best for: anyone whose writing happens inside Word and Outlook and who is already paying for Microsoft 365.

5. ProWritingAid — best for style-aware checking while you draft

Price: Free tier; Premium $10/month billed yearly ($120/year) at list, $7.50/month ($90/year) in a 25% sale running on 7 September 2026; $30/month billed monthly; lifetime $399 (ProWritingAid) Free tier: 500 words at a time, each report runnable twice per day Runs in: Word, Google Docs, a desktop editor and a browser extension Languages: English only — General, British, US, Australian and Canadian

ProWritingAid’s real-time checking does something the others do not: it flags stylistic problems as you write, not only errors. Overused words, sticky sentences, echoes and sentence-length monotony surface while you are drafting rather than in a report afterwards. If you want a checker with an opinion about your prose, this is it.

Limitations for sentence-level use: the free tier’s 500-word cap makes it a demo rather than a usable free checker, which is why it sits below QuillBot here despite being the stronger product overall. It is English-only, cloud-only, and its style flags are frequent enough to be noise for anyone writing short-form. The list price is close to notional given near-permanent discounting, and yearly plans carry only a three-day refund window.

Best for: people drafting long-form prose who want style feedback in the moment. Its document-level reports are covered on best AI proofreaders.

6. QuillBot — best free toolkit for students

Price (USD): free tier; Premium $19.95/month, $39.95 per three months, or $99.95/year ($8.33/month) at list — with a 40% promotion showing $5.00/month on 7 September 2026 (QuillBot) Free tier: grammar checking with no published word cap. QuillBot’s published caps sit on the other tools: paraphrasing at 125 words per pass, summarising at 1,200 words, AI detection at 1,200 words and ten scans per day Runs in: Chrome, Edge and Safari; Word add-in; Google Docs; macOS and Windows desktop; iOS and Android

QuillBot’s grammar checker is unremarkable and free, and it arrives attached to paraphrasing, summarising, translation, citation generation and AI detection in one account. For a student that bundle is the argument — checking is one job of five, and none of them cost anything at the free tier.

Limitations: the checker itself has no meaningful advantage over Grammarly’s free tier, and Grammarly runs in more places. QuillBot’s own premium page shows two different annual prices, $5.00 on the plan card and $8.33 in the comparison table beneath it. Note also that QuillBot, LanguageTool and Scribbr share one owner in Learneo, so treating them as independent alternatives is a mistake.

Best for: students who want checking, paraphrasing and citations in one free account. See also best AI study tools and best AI for students.

7. Sapling — best for teams writing to customers

Price: free tier; Pro $25/month or $12/month billed annually; Enterprise from 10 seats at $15 per seat per month (Sapling). One-month free Pro trial, no card. No promotion was showing on 7 September 2026 Free tier: 2,000 characters per check, 20 snippets, free domains only Runs in: Chrome, Firefox, Edge, Opera and Brave; Word, Outlook and PowerPoint; Google Docs, Slides and Sheets; Windows and macOS; plus Zendesk, Intercom, Salesforce, HubSpot, ServiceNow, Freshdesk and more than 30 other business systems Languages: ten, including US, UK, Canadian and Australian English

Sapling is the only tool here built for people typing into a support ticket rather than a document. It checks grammar, spelling, punctuation, tone and formality and readability inside the systems where customer conversations actually happen, which no general checker reaches.

Two things make it viable where the others are not. It offers a self-hosted deployment, so a company that cannot send customer text to a third party can still run inline checking, and it carries HIPAA, SOC 2 Type II, PCI, GDPR and CCPA compliance to go with it.

Limitations: the integrations that justify the price sit behind the paid “premium domains” tier, so the free plan checks you in browsers, email and documents but not in the helpdesk you actually work in. There is no mobile app. The pricing page never labels its currency. And its one published accuracy claim — neural models catching “about 60% more errors than rule-based checkers” (Sapling) — is self-generated and should carry no weight in a purchase decision.

Best for: a helpdesk or sales floor where the checker needs to live inside Zendesk or Salesforce rather than inside a word processor. See also best AI for email.

8. Apple Writing Tools — best free option on Apple hardware

Price: no subscription. Hardware-gated to Apple Intelligence-capable devices Runs in: system-wide on selected text, across Mail, Messages, Notes, Pages and third-party apps that adopt the standard text controls

Apple’s Proofread action corrects grammar, spelling and punctuation in selected text and returns an explanation for each change, with Show Original and Revert (Apple). Today it is invoked per selection, which makes it a correction command rather than a continuous checker — the gap that has kept it off most people’s shortlists.

That gap may be closing. Apple is replacing Writing Tools with Write with Siri in the next OS generation, first seen in iOS 27 beta 2 in June 2026, where 9to5Mac describes it as a feature you invoke to proofread something already written (9to5Mac, 22 June 2026). Before WWDC, Bloomberg reported that Apple was testing a dedicated grammar checker that surfaces suggested revisions next to the original text, accepted or rejected one at a time or all at once (MacRumors, 18 May 2026). Whether the shipping version checks continuously as you type is not yet confirmed by Apple.

Limitations: it is beta software until the OS ships, the feature set has moved between betas, and none of it works on older hardware. Correction quality has never been independently measured. Availability by region and language is worth checking before relying on it — as of 7 September 2026 this remains pre-release.

Best for: Mac, iPhone and iPad users who want competent correction without a subscription.

9. Antidote — best deep reference for English and French

Price: listed at approximately €59 per year, with a second language at roughly €30 more and a 30-day free trial. Druide prices regionally and does not publish a single global figure, so treat these as indicative rather than verified — precise current pricing is data not available Runs in: Word, Outlook, browsers, email clients and more than 20 other applications, on Windows, macOS, Linux, iOS and Android Languages: English and French

Antidote, from Quebec’s Druide informatique, is the outlier here: a paid desktop application rather than a cloud service, aimed at people who want to understand the correction rather than accept it. It bundles dictionaries, conjugation tables, synonym and combination guides and full grammar guides behind every flag, and it processes locally.

It is the standard tool in Canadian bilingual professional writing for a reason — its French correction is stronger than anything else on this page, and it treats English and French as first-class rather than treating French as a secondary language pack.

Limitations: the pricing opacity is a genuine mark against it. Two languages only. There is no free tier, and the interface is dense in a way that suits professionals and deters casual users.

Best for: bilingual English and French writers, translators, and anyone who wants the reasoning behind a correction.

10. Ginger — cheapest paid full-sentence correction

Price: a 50% promotion was running on 7 September 2026. List and promotional prices: monthly $13.00, promotional $6.50; quarterly $9.99, promotional $4.99 per month; annual $7.50, promotional $3.75 per month ($45.00 total); two-year $6.00, promotional $3.00 per month (Ginger store). 70% student and teacher discount. No free trial of Premium Runs in: Chrome and Edge extensions; Word add-in is Windows-only; macOS and Windows desktop; iOS and Android apps plus an Android keyboard Languages: correction in English; translation across more than 40

Ginger is the cheapest way to buy contextual full-sentence rewriting rather than word-level flagging, and it is one of only two tools here with a dedicated Android keyboard, which matters if most of your typing happens on a phone.

Limitations: its free-tier limits are unpublished by design — the terms state they can be changed at any time without notice, which makes the free version impossible to evaluate or rely on. The Word add-in is Windows-only. There is no free trial of Premium, only a seven-day refund window, and the near-permanent 50% promotion means the list price is fiction.

Best for: phone-first writers on a tight budget who want more than spellcheck.

11. Wordtune — best for rewriting a sentence you already wrote

Price (USD): free tier with unlimited grammar checking and 10 rewrites per day; Advanced $6.99/month monthly or $4.89/month billed annually for 30 rewrites a day; Unlimited $9.99/month monthly or $6.99/month billed annually; Business pricing is not shown on the pricing page (Wordtune) Runs in: browser extension, web editor, Word add-in Languages: English

Wordtune, from AI21 Labs, is a rewriter with a grammar checker attached rather than the reverse. Highlight a sentence and it returns several versions — shorter, more formal, more casual — which is a different job from correction and a genuinely useful one if your sentences are correct but clumsy.

Limitations: as a checker it is the thinnest tool on this page, which is why it ranks here despite a good free tier. English only. Its parent has been reported by third-party reviewers to have slowed development in favour of enterprise work; AI21 has not confirmed this and we treat it as unverified. If rewriting is what you actually want, best AI for writing covers stronger options.

Best for: non-native English writers whose grammar is fine and whose phrasing is stiff.

12. Chrome Proofreader API — best for building checking into your own site

Price: free. In origin trial, usable in production by registering your domain in Google’s origin trial programme (Chrome for Developers) Runs in: Chrome, as a JavaScript API backed by Gemini Nano on the user’s device

This is not a product you install; it is the reason the category’s economics may change. Chrome now exposes a Proofreader JavaScript API that returns grammar and spelling corrections with per-issue error-type labels, running entirely on the user’s machine — no API key, no network call, no per-token bill, and no page content leaving the device.

Google chose a typed, task-specific API over a generic prompt interface deliberately, so that results are comparable across sites rather than dependent on each developer’s system prompt. For any web application that currently pays for a grammar API, this is a free on-device alternative for Chrome users.

Limitations: Chrome only, an origin trial in Chrome 141 to 145 rather than a stable API, English in Google’s own examples, and it requires the Gemini Nano model on the device — Google’s stated requirements include 22GB of free storage, so it is far from universal. It does nothing for a writer who is not a developer.

Best for: developers adding checking to a web app. Compare with best LLM APIs for cloud alternatives.

13. Gboard — best for correcting on an Android phone

Price: free, included with Android Runs in: the Gboard keyboard, system-wide Languages: many

Gboard’s proofread, rephrase and tone tools sit behind the magic-wand icon in the keyboard and run on-device, so the text does not leave the phone (Google). For most Android users this is the correction they will actually use, because it is already installed and already in every text field.

Limitations: the proofreading tools require a recent device with Gemini Nano support, so on mid-range and older phones this section does not apply. Gboard’s always-on checking remains spelling-focused; the grammar work happens when you invoke it, not continuously. Microsoft SwiftKey takes the opposite approach, folding correction into its prediction engine rather than offering a separate proofread action, which makes it stronger at anticipating and weaker at fixing.

Best for: Android users on recent flagship hardware who want free correction without installing anything.

What your grammar checker sends to a server

This is the axis nobody in the category advertises, and for a lot of writing it decides the choice. A cloud checker transmits the text you are typing — including drafts of things you may never send.

If you are writing anything covered by legal privilege, patient confidentiality, an NDA or an unannounced corporate action, the top six rows are the shortlist and the price of every tool below them is irrelevant.

Free grammar checkers: what the caps actually are

“Free” means very different things here, and the differences are the whole decision.

The practical answer: if you want a free grammar checker and nothing else, install Grammarly’s free tier, or Harper if you want it offline. Everything else free in this category is either a preview of a paid product or restricted to one ecosystem.

Can you just use ChatGPT, Claude or Gemini?

For checking as you type, no — they are not in the text field with you, and the workflow of copying a sentence out and pasting a correction back is slower than an underline.

For checking a paragraph you have already written, yes, with one specific instruction. Research presented at the BEA 2026 workshop found that telling a model to make minimal edits rather than to “improve” text moved GPT-4.1’s precision on CoNLL-2014 from 57.26 to 70.37, with recall falling by an almost exactly equal amount (Türker and Eryiğit, 2026). Ask a model to proofread and you get a rewrite; ask it to correct only outright errors and change nothing else, and you get correction.

The risk is silent meaning change: the same body of work measured false insertion rates above 50% for adjectives and adverbs, meaning the model adds modifiers you never wrote. Most read well. Some change what the sentence claims.

There is also a cost specific to second-language writers. A May 2026 study polished argumentative essays by Chinese B2-level students through four leading models and found “a drastic collapse of dialogic engagement markers, turning negotiated discourse into monologic assertions” (Liu et al., 2026). The text came back more correct and less the writer’s own. A specialist checker underlines a comma; a general model rewrites your stance.

The practical stack: correct with a checker, and use a model only when the problem is phrasing rather than grammar.

Best AI grammar checker by use case

Best overall: Grammarly’s free tier. Full grammar and spelling checking, in more apps than anything else. Upgrade to Pro at $12/month only if you want rewriting and tone control. Grammarly

Best for more than one language: LanguageTool Premium, €59.89/year. More than 30 languages and dialect rules across six English variants. LanguageTool

Best for privacy: Harper. Runs entirely on your device, sends nothing anywhere, costs nothing, Apache-2.0. Harper

Best for developers: Harper as a language server, in VS Code, Neovim, Zed or Obsidian. For building checking into a web app, the free on-device Chrome Proofreader API.

Best if you already pay for Microsoft 365: Microsoft Editor, plus Copilot’s one-action fix-all in Word for the web. You are already paying for it. Microsoft Editor

Best for style feedback while drafting: ProWritingAid Premium, $120/year at list. Flags overused words, echoes and sticky sentences as you write. ProWritingAid

Best for a support or sales team: Sapling Enterprise, $15 per seat per month from 10 seats. The only checker inside Zendesk, Intercom, Salesforce and HubSpot. Sapling

Best for English and French: Antidote. Local processing and the deepest reference material in the category. Antidote

Best on a phone: Gboard’s proofread tools on a recent Android device, or Grammarly’s keyboard on any device. Both are free.

Best on Apple hardware: Apple’s Proofread action today, and Write with Siri once the next OS generation ships.

Best for students: QuillBot’s free tier, which bundles checking with paraphrasing and citations. See best AI for college students.

Cheapest paid option: Ginger at $45/year promotional, with the caveat that the promotion is close to permanent and the free tier is unpublished.

What AI grammar checkers still get wrong

They are near-blind to structure and meaning. The best result in the last multi-tool academic comparison was 44.4% overall accuracy, with 99% on spelling and under 11% on sentence-structure errors (Sahu et al., 2020). The shape of that finding has not been contradicted since. A sentence that is grammatical and untrue passes every tool here.

They miss about half of what is there. The one independent measurement of a commercial checker found 51.1% recall (Wu et al., 2023). A clean document is not a correct document; it is a document with no flagged errors.

They flatten second-language voices. The engagement-marker collapse measured by Liu et al. (2026) is a real cost of accepting suggestions uncritically, and it lands hardest on the writers who use these tools most.

Reference-based scoring penalises valid choices. Articles and prepositions frequently have several defensible answers. Writers from languages without article systems get marked wrong for choices that are grammatically fine, and that bias flows from the benchmarks into the products trained against them.

Nothing here is a proofreader. A real-time checker cannot see that an acronym was defined differently forty pages ago, because it is only ever looking at one sentence. That is a different tool and a different page.

Frequently asked questions

What is the best AI grammar checker in 2026?

Grammarly’s free tier is the best AI grammar checker for most writers in September 2026. Grammar, spelling, punctuation and tone detection are all included at no cost, subject to the same document limits as the paid plan, and Grammarly runs in browsers, Microsoft Office, Google Docs, desktop apps and mobile keyboards, which is wider reach than any competitor. Paying $12 per month for Grammarly Pro adds rewriting, tone adjustment and generative prompts rather than better error detection. Writers working in more than one language should use LanguageTool instead, and anyone who cannot send text to a cloud service should use Harper.

Is there a genuinely free AI grammar checker?

Yes, three of them. Grammarly’s free tier checks grammar, spelling and punctuation, with the same document limits as Pro, and is a permanent plan rather than a trial. Harper is free forever under the Apache-2.0 licence, runs entirely offline on your own device, and is developed at Automattic. QuillBot’s free tier includes grammar checking alongside limited paraphrasing and AI detection. LanguageTool’s free tier is capped at 2,000 characters per text field and its browser extension now requires a Premium subscription, while ProWritingAid caps free users at 500 words at a time, which makes both previews rather than free products.

What is the difference between a grammar checker and a proofreader?

A grammar checker works at sentence level and flags errors in the sentence in front of it, such as a subject-verb disagreement or a missing comma, usually in real time as you type. A proofreader works at document level and additionally checks a finished document against itself, catching inconsistencies that are only errors in context — an acronym defined twice, hyphenation that changes between chapters, or a citation style applied unevenly — and the tools built for it return a Word file with every edit as a tracked change. Every proofreader contains a grammar checker; most grammar checkers are not proofreaders.

How accurate are AI grammar checkers?

There is no honest single figure, because no vendor publishes precision or recall for its live checker and no independent 2026 test of these products exists. The one independent measurement of any commercial checker on a public benchmark put Grammarly at 67.3% precision and 51.1% recall on 100 CoNLL-2014 sentences in 2023, which describes a tool that is right when it speaks and says nothing about roughly half the errors in front of it. That precision-first bias is deliberate: the field’s standard metric weights precision twice as heavily as recall, on the reasoning that a false underline annoys a writer more than a missed comma. The reliable generalisation is that these tools are near-perfect on spelling, competent on mechanical grammar, and should not be trusted on sentence structure or meaning.

Which AI grammar checker works offline?

Harper runs entirely on your device under an Apache-2.0 licence, returns suggestions in under 10 milliseconds, and makes no network requests at all. Antidote is a desktop application that processes locally in English and French. Chrome’s Proofreader API runs on-device through Gemini Nano, and Gboard’s proofread tools do the same on Android devices with the necessary hardware. LanguageTool and Sapling can both be self-hosted so text stays on your own infrastructure. Grammarly, Microsoft Editor, ProWritingAid, QuillBot, Ginger and Wordtune are cloud-only and transmit your text to be checked.

Is Grammarly worth paying for in 2026?

Only if you want more than grammar checking. The free tier already covers grammar, spelling, punctuation and tone detection across every app Grammarly supports, so paying $12 per month on an annual plan buys full-sentence rewrites, tone adjustment, inclusive-language suggestions, plagiarism detection and 2,000 AI prompts per month instead of 100. If your problem is typing errors, the free tier is the product. If you want the tool to rewrite your sentences rather than flag them, Pro is worth it.

What is the best free grammar checker for students?

QuillBot’s free tier is the strongest single choice for students, because grammar checking arrives bundled with paraphrasing, summarising, translation and citation generation in one free account. Grammarly’s free tier is the better pure checker and runs in more places, so many students use both. Note that most institutions distinguish between correcting your own writing and having a tool rewrite it, and that accepting large-scale rewrites is what raises academic-integrity questions rather than fixing a comma. Our pages on the best AI for students and the best AI study tools cover the wider stack.

Does using a grammar checker get my writing flagged as AI-generated?

Fixing a comma or a misspelling changes almost nothing a detector measures, so ordinary use of a real-time checker is not what causes a flag. The line falls at the point where you stop correcting and start accepting rewrites: a suggestion that replaces your whole sentence replaces your sentence structure with the model’s, and sentence structure is exactly what detection systems score. This is one practical reason to stay on a free tier that only underlines errors rather than a paid tier that offers to rewrite them. Institutional policies vary widely and some prohibit any AI assistance at all regardless of scope, so the rule that binds you is your institution’s, not the vendor’s marketing. How the detection itself works is covered on our best AI detector page.

Which grammar checker supports British and Australian English?

LanguageTool supports British and American English among more than 30 languages and applies dialect-specific rules across six English variants. ProWritingAid supports General, British, US, Australian and Canadian English. Sapling supports US, UK, Canadian and Australian English. Grammarly lets you set a language preference including British, Australian, Canadian and Indian English. Harper supports British, American, Canadian, Australian and Indian English. Where a tool does not state its supported variants, assume US English and check before you buy.

Can ChatGPT or Claude replace a grammar checker?

Not for real-time correction, because they are not in the text field as you type and copying text out and back is slower than an underline. For checking a finished paragraph they work well, provided you instruct them to make minimal edits and change nothing else — research presented at the BEA 2026 workshop found that switching from an open-ended proofreading instruction to an explicit minimal-edit instruction raised GPT-4.1’s precision from 57.26 to 70.37 on CoNLL-2014. The risk is silent meaning change: a 2026 study measured false insertion rates above 50% for adjectives and adverbs, meaning the model adds words the writer never used.

What is the best grammar checker for Word?

Microsoft Editor, because it is already built into Word and included with any Microsoft 365 subscription, and Microsoft 365 Copilot in Word for the web can now apply every grammar and spelling correction in a single action. Grammarly, ProWritingAid, QuillBot and Sapling all offer Word add-ins if you want a second opinion or features Editor lacks, and Ginger offers one on Windows only. Note that Word’s Similarity Checker is being retired on 3 October 2026, though Microsoft states the grammar, spelling and citation features are unaffected.

Is there a good grammar checker for a phone keyboard?

Yes, three worth using. Gboard’s proofread, rephrase and tone tools run on-device on Android phones with recent hardware and cost nothing. Grammarly offers keyboards for both iOS and Android tied to the same free account as its desktop product. Ginger offers an Android keyboard on its paid tiers. On iPhone and iPad, Apple’s own Proofread action already works on selected text system-wide, and Apple is replacing Writing Tools with Write with Siri in the next OS generation, with a dedicated grammar checker reported by Bloomberg but not yet confirmed as continuous.

How to choose in September 2026

Start from three tests, in this order.

Text that has to stay on your machine. If that is you, the list is Harper, Antidote, a self-hosted LanguageTool or self-hosted Sapling, and nothing else on this page qualifies at any price.

Writing in more than one language. If that is you, it is LanguageTool, or Antidote for English and French specifically.

If neither applies — and for most people neither does — install Grammarly’s free tier and stop. It checks grammar everywhere you type, at no cost, and the paid upgrade sells rewriting rather than better checking. Add ProWritingAid if you want style feedback while drafting, or Sapling if you are equipping a customer-facing team.

Two things to hold onto. First, the free tiers are where the real differences are: Grammarly, Harper and QuillBot give you a working checker for nothing, while LanguageTool’s 2,000 characters and ProWritingAid’s 500 words are demonstrations. Second, nobody in this category will tell you how accurate their product is, the last independent measurement of any of them was a 100-sentence test in 2023, and every ranking that claims to have “tested” these tools scored them itself. Anyone quoting you an accuracy percentage for a grammar checker is quoting something they did not measure.