Best AI Grammar Checkers 2026: Ranked by What They Actually Catch

The name on the category for a reason: Grammarly's corrections are the most polished here, its explanations actually teach, and it lives nearly everywhere — browser, Word, desktop, phone keyboard. The paid tier (renamed Pro) adds the things people actually renew for: full-sentence rewrites, tone adjustments, plagiarism checking against web sources, and style rules you can set per document. Free is a real tool, not a demo: core grammar, spelling and punctuation, no card required.

The honest limits: it's English-only, its suggestions occasionally sand the personality out of deliberate prose, and the pricing spread is wide — Pro runs about $12 a month when billed annually (roughly $144 a year) but the month-to-month price is dramatically higher, near $30 (verify current). If you write in English daily and the stakes are professional, it's still the default answer to Rico's question.

The multilingual champion — and that's not a participation trophy. LanguageTool checks grammar and style across 25+ languages, so if your week mixes English, French, German or Spanish, one extension covers the whole map where Grammarly can't follow at all. It lives in browsers, Word and as a stand-alone editor, and the free tier works without even an account, which is rarer than it should be.

Its English suggestions are solid but a step less sharp than Grammarly's best catches, and the free tier has character caps per check that heavy writers will hit (published figures for the cap differ across sources — verify on the site). Premium has been reported around $59.90 a year with promotional pricing common (verify current). If your life happens in more than one language, this is the answer and there isn't really a second option.

The writing coach for people who write books. Where Grammarly fixes sentences, ProWritingAid interrogates manuscripts: repeated words, pacing, sticky sentences, overused adverbs, readability by chapter — twenty-odd reports that read like an editor's letter. For novelists and long-form nonfiction, no other tool here thinks at that altitude, and paid plans carry no word limits.

The honest trade-offs: it's English-only, the interface assumes you want homework with your corrections, and casual writers will feel buried. Pricing moved recently — the old cheap annual plan is gone; Premium now runs about $120 a year ($10 a month billed annually) or roughly $30 month-to-month, with a one-time lifetime option around €399 and a higher Premium Pro tier adding AI features (verify current). Buy it for the manuscript, not the email.

The free-tier king. QuillBot bundles grammar checking with a genuinely useful paraphraser, summarizer and citation machine, and the free plan gives you working versions of all of them — which is why students and budget-conscious writers land here first and stay longer than expected. When a sentence is grammatically fine but just wrong, its rephrase modes are often the faster fix than rewriting it yourself.

The meter is the catch: free paraphrasing caps at 125 words at a time and some tools get a few uses a day, so volume pushes you toward Premium — reported around $10 a month billed annually up to roughly $19.95 month-to-month, with constant discounts (verify current). Grammar detection itself is a step below Grammarly on subtle errors. Best framing: the best free kit in the category, with a paid ceiling.

The rewording specialist. Wordtune's core trick is offering several alternative phrasings for any sentence — shorter, longer, more formal, more casual — so you pick a voice instead of accepting a correction. For non-native English writers polishing emails, that menu of options teaches more than a red underline ever does, and the extensions work across most places you type.

It's a narrower tool than the giants: grammar checking exists but isn't the headline, the free tier allows only a handful of rewrites a day, and paid tiers have been reported from about $6.99 a month (annual) to around $9.99 for unlimited (verify current). Think of it as the seasoning shelf, not the kitchen — brilliant for making a sentence yours, not for catching every comma crime.

The free phrase-fixer from the translation people. DeepL Write takes your sentence and returns cleaner, more natural versions — fixing errors along the way — with a tone dial for formal or casual registers. Because it's built by DeepL, the phrasing instincts are unusually good, and the whole thing is free at the moment, no account gymnastics required (verify current; free tools can grow paywalls).

The honest limits: it covers a small set of languages rather than the full DeepL roster, it works text-by-text rather than living inside every app you write in, and it's a rewriter more than a proofreader — you won't get a full-document audit. Use it as the last pass on important paragraphs, the thing you paste a client email into before sending, and it earns its zero price tag.

The checker your computer already has. Editor is built into Word, Outlook and Edge: grammar, spelling and basic refinements at no cost, with deeper style checks — clarity, conciseness, formality — for Microsoft 365 subscribers. For anyone inside the Microsoft house, the absence of setup is the feature: it's simply there, in the document, the moment you mistype.

Outside that house it's unremarkable, and its suggestions sit a clear notch below Grammarly's polish on tone and nuance — fine for catching errors, weaker on making prose sing. The advanced checks also ride the Microsoft 365 subscription, so "free" depends on what your employer or household already pays (verify current). Default inside Office; nobody's reason to switch into it.

The drill sergeant. Hemingway doesn't negotiate: it highlights long sentences, passive voice, adverbs and readability grade in bright, accusatory colors until your prose does push-ups. It won't catch a subject-verb disagreement, and it doesn't pretend to — what it catches is the bloat that makes readers stop reading. As a discipline tool for drafts that meander, nothing here is more bracing.

The web version is free; the desktop app is a small one-time purchase (reported around $19.99 — verify current). But it's a style coach, not a grammar checker in the proper sense: pair it with a real proofreader rather than replacing one, and ignore it when the flatness it pushes for isn't what the piece needs. Brevity is a virtue; it isn't the whole faith.