Best AI Grammar Checkers Compared

How We Evaluated These Tools

We tested each grammar checker against a standardized set of 200 sentences containing deliberate errors across eight categories: spelling, contextual spelling (homophones), subject-verb agreement, pronoun errors, punctuation, passive voice, wordiness, and comma placement. Each tool was scored on its detection rate (percentage of errors caught), false positive rate (number of correct constructions flagged as errors), and suggestion quality (whether the proposed fix was correct and maintained the original meaning).

Beyond raw accuracy, we evaluated real-world usability: how the tool integrates into daily writing workflows, whether suggestions appear fast enough to be useful without disrupting typing, how well the tool handles domain-specific vocabulary, and whether the pricing model delivers fair value for the features offered. A grammar checker that catches 95% of errors but only works in one browser extension is less useful than one that catches 90% but works across email, documents, messaging, and mobile.

1. Grammarly: Best Overall Grammar Checker

Grammarly detected 94% of errors in our test set, the highest overall detection rate, with a false positive rate of just 2.3%. Its contextual spelling detection is particularly strong: it correctly identified "compliment" vs "complement," "principal" vs "principle," and "stationary" vs "stationery" in every test sentence where these words were misused. Style suggestions were relevant and well-calibrated, flagging genuine wordiness and passive voice overuse without being so aggressive that accepting every suggestion would flatten the writing.

The integration coverage is what separates Grammarly from every competitor. The browser extension works in Gmail, Google Docs, LinkedIn, Twitter/X, Reddit, Slack, and virtually every web-based text field. The desktop app adds Microsoft Word and Outlook support on both Windows and Mac. The mobile keyboard works on iOS and Android across every app. For writers who need a single tool that works everywhere without manual copy-paste, nothing else comes close.

GrammarlyGO, the generative AI feature, adds full-sentence and full-paragraph rewriting that goes beyond correction into composition assistance. You can highlight a paragraph and ask GrammarlyGO to make it shorter, more formal, more engaging, or clearer, and it generates multiple options. This feature blurs the line between grammar checker and writing assistant, and it is included in the Premium plan at no additional cost.

The weakness is price. At $12 per month (annual billing) or $30 per month (monthly billing), Grammarly Premium costs more than most competitors. The free tier is useful but noticeably limited once you have experienced the Premium features, particularly the style suggestions, tone detection, and full-sentence rewrites that make the biggest difference in writing quality.

2. ProWritingAid: Best for Long-Form Writers

ProWritingAid detected 91% of errors in our test set, slightly behind Grammarly on raw accuracy, but offers significantly deeper analysis through its suite of over 20 writing reports. The tool's strength is not in catching individual errors but in diagnosing patterns across an entire document. The Overused Words report highlights repeated vocabulary. The Sentence Length report visualizes sentence length variation to identify monotonous passages. The Sticky Sentences report flags sentences overloaded with common function words. The Consistency Check ensures that style choices (capitalization, hyphenation, spelling variants) remain uniform throughout the document.

For novelists and creative writers, ProWritingAid's fiction-specific features are unmatched. The Dialogue Tags report identifies overuse of alternatives to "said" (a common novice writer mistake). The Pacing report highlights sections where description, dialogue, and action are imbalanced. The Echoes report catches word repetitions within short distances that a human editor would flag but that other grammar checkers miss entirely. Integration with Scrivener, the dominant writing tool for fiction authors, makes ProWritingAid the default choice in the creative writing community.

The $399 lifetime license is ProWritingAid's most compelling feature. For writers who will use a grammar checker for years, paying once eliminates subscription fatigue and delivers the best long-term value of any tool on the market. The monthly plan at $10 per year is competitive with Grammarly, and there is a free tier with limited checks per day that is useful for evaluation.

The main drawback is that ProWritingAid's real-time checking in browser extensions and Google Docs is slower than Grammarly's. Suggestions take a beat longer to appear, and the extension occasionally struggles with very long documents in Google Docs. The desktop app is faster, but the browser experience is where most people first encounter the tool.

3. LanguageTool: Best for Multilingual Writers

LanguageTool detected 87% of errors in our English test set, behind both Grammarly and ProWritingAid, but it is the only serious grammar checker that supports over 30 languages with dedicated grammar rules for each one. The German, French, Spanish, and Portuguese grammar checking is genuinely useful, not just spell-checking with a translated interface but actual grammatical analysis with rules written by native-speaker linguists.

The open-source foundation is a meaningful differentiator. The grammar rules are publicly auditable on GitHub, and organizations with strict data governance requirements can self-host the tool on their own infrastructure. This makes LanguageTool the only grammar checker that can be deployed without sending any text to a third-party server, a requirement for legal, medical, and government organizations that handle sensitive documents.

At $4.99 per month (annual billing), LanguageTool Premium is the most affordable paid grammar checker with meaningful capabilities. The Premium plan adds the "picky mode" that catches additional stylistic issues, removes the character-per-check limit, and adds team features for organizational use. The free tier allows 10,000 characters per check with basic error detection, which is generous enough for most individual documents.

The limitation is that LanguageTool's AI-powered style suggestions lag behind Grammarly and ProWritingAid. The tool catches errors reliably, but its suggestions for improving clarity, tone, and conciseness are less sophisticated. For writers who primarily need error correction rather than style coaching, this tradeoff is acceptable. For writers who want a tool that actively improves their prose, Grammarly or ProWritingAid will deliver more value.

4. Ginger Software: Best for ESL Writers

Ginger detected 85% of errors in our general test set, but its performance on ESL-specific error patterns was notably stronger than generalist competitors. It correctly handled article insertion and deletion (a/an/the errors), preposition selection ("arrive to" corrected to "arrive at," "interested for" corrected to "interested in"), and word order issues ("always I go" corrected to "I always go") at a higher rate than Grammarly on these specific categories.

The built-in translator supports over 40 languages and allows ESL writers to input text in their native language and receive an English translation with grammar checking applied to the result. The text-to-speech feature helps with pronunciation practice, and the personal trainer module tracks recurring error patterns and provides exercises to address them. No other grammar checker combines correction with active language learning in a single tool.

The interface and browser extension are less polished than Grammarly's, and the tool's general-purpose grammar checking is a step behind the top tier. But for its target audience, the combination of ESL-specific correction, translation, pronunciation, and learning features makes Ginger the most comprehensive option available.

5. Wordtune: Best for Sentence-Level Rewrites

Wordtune approaches grammar checking from a different angle than traditional tools. Rather than highlighting errors and offering single-word corrections, Wordtune generates full alternative phrasings for any sentence you select. You can request rewrites that are more casual, more formal, shorter, longer, or simply different, and the tool produces three to five options instantly. This workflow is exceptionally useful for writers who know what they want to communicate but struggle to find the right phrasing.

The grammar correction that happens alongside rewriting is competent: Wordtune caught 82% of errors in our test set, which is adequate but behind the dedicated grammar checkers. Its strength is not in error detection but in improving the quality of grammatically correct but poorly phrased writing. A sentence that is technically error-free but reads awkwardly will not be flagged by Grammarly or ProWritingAid unless it triggers a specific style rule, but Wordtune will offer cleaner alternatives simply because its rewrite engine produces better phrasing.

The free tier includes 10 rewrites per day, which is enough for light use. The Premium plan at $9.99 per month unlocks unlimited rewrites, the ability to rewrite entire paragraphs, and a "spice" feature that adds specific elements (examples, counterarguments, analogies) to selected text.

6. QuillBot Grammar Checker: Best Free Grammar Checking

QuillBot's grammar checker is the most generous free option on the market, offering unlimited grammar checks with no character limit and no daily restriction. The detection rate of 80% in our test set is the lowest among the tools reviewed here, but for writers who need basic error correction without paying anything, QuillBot catches the errors that matter most: misspellings, clear grammatical mistakes, punctuation errors, and the most common homophones.

The grammar checker is part of QuillBot's broader writing toolkit, which includes a paraphrasing tool, summarizer, citation generator, and translator. The integration between these tools is seamless: you can paste text, check grammar, paraphrase it, and check grammar again on the paraphrased output, all within the same interface. This workflow is popular with students who use QuillBot extensively for research writing.

The Premium plan at $9.95 per month adds more paraphrasing modes and a plagiarism checker but does not significantly upgrade the grammar detection capabilities. For users who need better grammar checking, the paid tiers of Grammarly, ProWritingAid, or LanguageTool offer more value than QuillBot Premium.

Quick Comparison Summary

Grammarly leads on accuracy (94%), integrations, and all-around polish but is the most expensive at $12 per month. ProWritingAid is the deepest tool for long-form analysis (91% accuracy) with a unique lifetime license at $399. LanguageTool offers the best multilingual support and privacy (87% accuracy) at the lowest price of $4.99 per month. Ginger is purpose-built for ESL learners (85% accuracy) with translation and learning features. Wordtune excels at sentence-level rewrites (82% accuracy) rather than traditional error checking. QuillBot offers the most generous free grammar checking (80% accuracy) as part of a broader writing toolkit.

For most writers, the decision comes down to two choices: Grammarly if you want the best overall tool and are willing to pay for it, or LanguageTool if you want strong error correction at a lower price. Writers with specific needs, such as long-form manuscript editing (ProWritingAid), ESL learning (Ginger), or sentence-level polishing (Wordtune), should choose the tool built for their use case rather than the one with the highest overall score.