8 Best AI Grammar Checkers in 2026 (Free & Paid, Ranked)

Grammarly is the benchmark for AI grammar checking — 30 million daily users don't lie. Beyond catching comma splices and misspellings, Grammarly's AI analyzes tone, formality level, and audience fit, then suggests rewrites that match your intended voice. The Premium tier adds clarity rewrites, full-sentence restructuring suggestions, and a plagiarism checker. Business tier adds brand guidelines enforcement and a shared style guide across your team. The browser extension covers everything you type — Gmail, Google Docs, Notion, LinkedIn, Slack — making it the most frictionless grammar checker available. The free tier catches most errors but gates the best AI suggestions behind Premium ($12/mo annually).

Wordtune goes further than grammar checking — it rewrites entire sentences to make them clearer, shorter, more formal, or more casual, depending on what you need. Where Grammarly identifies a problem and suggests one fix, Wordtune gives you 5-7 rewrite options for each sentence, letting you choose the phrasing that matches your voice. The 'Spices' feature adds specific improvements: add a statistic, add an example, make this funnier, or make this more professional — triggered on individual sentences. For non-native English speakers, Wordtune's rewrite suggestions are particularly valuable because they produce natural-sounding English rather than grammatically correct but stilted sentences.

QuillBot is the most widely used free AI grammar checker among students, and for good reason — the free tier is genuinely useful rather than a demo. The Grammar Checker catches errors in real-time with clear explanations of what's wrong and why. The Paraphraser rewrites text in 8 different modes (Standard, Fluency, Formal, Academic, Simple, Creative, Shorten, Expand), which is particularly useful for academic writing. QuillBot's Summarizer, Citation Generator, and Translator round out a suite that covers most student writing needs without a paid plan. The Premium tier ($9.95/mo annual) removes word limits and adds more paraphrasing modes, but the free tier handles routine grammar checking well.

LanguageTool is the strongest multilingual AI grammar checker available, covering 30+ languages with genuine depth — not just English checked for obvious errors. For writers who work in German, French, Spanish, Portuguese, or Dutch, LanguageTool's rule-based accuracy in those languages exceeds what Grammarly offers (which is primarily English-optimized). The open-source core means the privacy-conscious can self-host and run checks locally without sending text to external servers — unique among grammar tools. The browser extension, Google Docs add-on, and LibreOffice plugin cover most writing environments, and the free tier is more generous than Grammarly's for basic error checking.

ProWritingAid is the most comprehensive AI grammar checker for authors writing novels, non-fiction books, and long-form content. Beyond grammar and spelling, ProWritingAid runs 25+ different style reports: sentence length variation, dialogue tag analysis, pacing checks, overused words, repeated phrases, and readability scores calibrated to genre. The sticky sentences report identifies constructions that slow readers down — invisible to standard grammar checkers. For Scrivener users, ProWritingAid's native Scrivener integration is the best in the market. The lifetime plan ($399 one-time) makes it significantly cheaper than Grammarly over 3+ years of use, which matters for authors writing multiple books.

Hemingway Editor doesn't check grammar — it checks readability. The tool highlights sentences that are hard to read (yellow), very hard to read (red), passive voice uses, adverbs, and complex phrases with simpler alternatives. The goal is Hemingway-style clarity: short sentences, active voice, no unnecessary words. For content marketers, bloggers, and business writers who need to communicate clearly to a broad audience, Hemingway Editor enforces a readability discipline that grammar checkers don't. The free web version (hemingwayapp.com) handles routine checks without an account. The desktop app ($19.99 one-time) adds direct publishing to WordPress and Medium.

Writer.com is an enterprise AI writing platform with grammar checking built into a broader content governance system. The grammar checker enforces company-specific style rules — not just standard English, but your brand's preferred vocabulary, banned phrases, and tone guidelines. For legal teams, Writer checks for compliance-risky language automatically. For marketing teams, it flags off-brand terminology and enforces approved product naming. The Co-writer (built on Writer's own Palmyra LLM) generates content within your brand guidelines, so everything produced stays consistent. Enterprise pricing puts Writer out of reach for individuals, but for teams producing high volumes of brand-sensitive content, it's the most capable option.

Sapling is a grammar checker designed specifically for customer-facing teams — support agents, success managers, and sales reps who type dozens of messages per day across multiple platforms. It integrates with Zendesk, Salesforce, HubSpot, Intercom, and 50+ CRMs to check grammar and suggest complete response snippets in real-time as agents type. The autocomplete suggestions finish sentences based on your team's highest-performing historical responses. Quality scores track response quality across the team and identify agents who need coaching. For support teams handling 100+ tickets per day, Sapling reduces response time and error rates simultaneously — a different use case than personal writing improvement.