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LanguageTool is a grammar, style, and spelling checker built on an open-source LGPL-licensed core, first released by Daniel Naber in 2003. LanguageTool Premium adds AI-powered rephrasing, a 150,000-character limit per text field, and advanced style rules on top of the free open-source engine.
What Is LanguageTool?
LanguageTool is a proofreading and writing-assistant platform that combines a free, open-source rule-based grammar engine with a paid Premium tier for deeper style, punctuation, and AI-paraphrasing checks across 30+ languages. The open-source core runs under the GNU Lesser General Public License (LGPL) and remains downloadable and self-hostable from its GitHub repository. LanguageTooler GmbH, the company behind LanguageTool, operates the hosted web service, browser add-ons, and Premium subscription layered on top of that core. Learneo, Inc. acquired LanguageTool in April 2023 and continues to fund its AI writing development.
| Attribute | Value |
|---|---|
| Founded | 2003 (Daniel Naber, diploma thesis project) |
| Parent company | LanguageTooler GmbH, acquired by Learneo, Inc. in April 2023 |
| Core license | GNU Lesser General Public License (LGPL 2.1+) |
| Free tier character limit | 2,000 characters per text field |
| Premium character limit | 150,000 characters per text field |
| Languages supported | 30+, including English, German, Spanish, French, Dutch, Polish, Portuguese |
| Platforms | Chrome, Edge, Firefox, Safari, Opera, Word, Google Docs, LibreOffice, Gmail, Outlook, Apple Mail, Thunderbird, Windows, macOS |
LanguageTool differentiates itself from Grammarly through its open-source core: developers can clone the repository, run the engine offline, and inspect or extend its XML and Java-based grammar rules directly, an option Grammarly’s closed-source architecture does not offer.
What Are LanguageTool’s Key Features?
LanguageTool’s Premium tier expands character limits to 150,000 per text field, unlocks unlimited AI sentence rephrasing, and adds a custom Style Guide for enforcing consistent wording across a document or team. The feature set spans five detection categories and multiple deployment surfaces.
- Detect grammar and punctuation errors across 10 sub-categories, including incorrect word order, wrong tense use, missing commas, and agreement errors.
- Flag style issues such as wordiness, repetition, informal phrasing, and overused words, with Premium adding over 20,000 additional English-language style checks.
- Correct spelling mistakes, including misspelled names, acronyms (e.g., flagging “HIPPA” and suggesting “HIPAA”), and casing errors on proper nouns.
- Verify semantic accuracy, such as catching an incorrect date-to-weekday pairing or confused word pairs like “precedence” versus “precedent.”
- Standardize formatting, including inconsistent number notation, incorrect currency placement, and non-metric measurement units.
- Rephrase sentences with unlimited AI-powered paraphrasing on Premium, versus 3 rephrasings per day on the free plan.
- Build a personal or team Style Guide with custom wording rules enforced across every check.
- Install the checker across 5 browsers, 4 email clients, 4 office suites, and native Windows and macOS apps, all syncing through one account.
- Store technical terms and unique phrases in a personal or Team Dictionary to eliminate repeat false-positive flags.
How Much Does LanguageTool Cost?
LanguageTool offers a free plan capped at 2,000 characters per check, a Premium plan for individuals starting around $4.99 per month when billed annually, and a Teams plan priced per user for groups of up to 20 members. Pricing is billed in four intervals — monthly, quarterly, annual, and two-year — with longer commitments lowering the effective monthly rate, according to LanguageTool’s official pricing page and third-party pricing trackers that monitor the vendor’s live rates.
| Plan | Price | Character limit | Best for |
|---|---|---|---|
| Free | $0 | 2,000 characters/check, 3 AI rephrasings/day | Casual proofreading |
| Premium | From ~$4.99/month (billed annually) | 150,000 characters/check, unlimited AI rephrasing | Individual professionals and writers |
| Teams | Per-user pricing, up to 20 members | 150,000 characters/check, shared Style Guide and Dictionary | Small teams needing consistent brand voice |
LanguageTool backs every Premium purchase with a 14-day money-back guarantee, and subscriptions cancel at any time without a notice period, taking effect at the end of the current billing cycle. LanguageTool for Business and self-hosted deployments carry custom, quote-based pricing outside the standard Premium and Teams tiers.
What Are the Pros and Cons of LanguageTool?
LanguageTool’s core advantage is its open-source, self-hostable engine paired with 30+ language support, while its main drawback is a less polished interface and narrower AI-writing feature set compared to closed-source competitors like Grammarly. The open-core model gives LanguageTool a structural advantage among proofreading tools: no other mainstream grammar checker publishes its full rule engine on GitHub under an LGPL license.
Pros:
- Open-source core engine, inspectable and self-hostable via the official GitHub repository
- 30+ supported languages, exceeding Grammarly’s English-and-limited-language focus
- GDPR-compliant hosting, with LanguageTooler GmbH based in Germany
- Browser add-on does not store typed text by default, per LanguageTool’s own privacy documentation
- Premium pricing undercuts Grammarly Premium, which typically starts near $12 per month
Cons:
- Free-tier character limit of 2,000 per check is restrictive for long-form drafts
- Interface and suggestion UX are less refined than Grammarly’s consumer-facing design
- AI rephrasing is capped at 3 uses per day on the free plan
- Plagiarism checking is not included in standard Premium or Teams tiers
- Support is limited to FAQ, forum, and phone channels, with mixed user reports on response speed
How Does LanguageTool Compare to Grammarly?
LanguageTool undercuts Grammarly on price and multilingual coverage, while Grammarly leads on interface polish, AI-writing depth, and integrated plagiarism detection. Both tools check grammar, punctuation, and style in real time across browsers and office apps, but they diverge on licensing model and language breadth.
| Factor | LanguageTool | Grammarly |
|---|---|---|
| Core license | Open-source (LGPL) | Proprietary, closed-source |
| Free-tier limit | 2,000 characters/check | 100 AI prompts/month (varies by feature) |
| Languages supported | 30+ | Primarily English, with limited additional-language support |
| Entry Premium price | ~$4.99/month (annual billing) | ~$12/month (annual billing) |
| Plagiarism checker | Not included in standard tiers | Included on Premium |
| Self-hosting option | Yes, via open-source core | No |
For a full feature-by-feature breakdown, see our dedicated Grammarly vs LanguageTool comparison.
Who Should Use LanguageTool?
LanguageTool suits multilingual writers, privacy-conscious teams, and developers who want a self-hostable grammar engine, while budget-focused solo writers benefit from its lower Premium price relative to Grammarly. Four user profiles get the most value from the platform.
- Multilingual content teams writing across German, Spanish, French, Dutch, Polish, or Portuguese in addition to English, where LanguageTool’s 30+ language coverage exceeds most English-first competitors.
- Privacy-conscious businesses operating under GDPR that need a Germany-based vendor and a browser add-on that avoids storing typed text by default.
- Developers and technical writers who want to self-host the open-source core, inspect rule logic on GitHub, or integrate the Proofreading API into an internal tool.
- Budget-conscious solo writers and students who need Premium-level style checking without paying Grammarly’s higher entry price.
What Are the Best Alternatives to LanguageTool?
Grammarly, ProWritingAid, and QuillBot rank as the three leading alternatives to LanguageTool, each trading LanguageTool’s open-source multilingual model for deeper single-language AI-writing features.
- Grammarly offers a more polished English-language interface and integrated plagiarism detection, at a higher Premium price point. Read our full Grammarly Review.
- ProWritingAid targets long-form authors with in-depth style reports and editing analytics beyond real-time grammar flags.
- QuillBot focuses on AI paraphrasing and summarization as its primary feature, with grammar checking as a secondary function.
Frequently Asked Questions
Is LanguageTool actually free? Yes. LanguageTool’s Free plan checks up to 2,000 characters per text field with core grammar and spelling detection, no credit card required, and it never expires.
Is LanguageTool open source? Yes. The LanguageTool core engine is published on GitHub under the GNU Lesser General Public License (LGPL 2.1 or later) and can be self-hosted or modified.
Does LanguageTool support languages other than English? Yes. LanguageTool supports 30+ languages and dialects, including German, Spanish, French, Dutch, Polish, Portuguese, and Catalan, each maintained by volunteer language contributors.
Can I cancel LanguageTool Premium anytime? Yes. LanguageTool Premium subscriptions cancel at any time with no notice period, and cancellation takes effect at the end of the current billing cycle. LanguageTool also offers a 14-day money-back guarantee on Premium purchases.
The Verdict
LanguageTool Premium costs less per month than Grammarly Premium while covering more than six times as many languages, making it the more cost-effective choice for multilingual and privacy-focused writers, though Grammarly still leads on interface polish and built-in plagiarism detection.