LanguageTool

What Is LanguageTool?

Most grammar checkers are built in Silicon Valley, designed for English, and treat every other language as an afterthought. LanguageTool took the opposite approach. Created in 2003 by Daniel Naber in Potsdam, Germany, it started as an open-source academic project and grew into one of the most capable multilingual writing tools on the market — supporting more than 30 languages with native-quality rule sets.

The product is now available everywhere you write: browser extensions for Chrome, Firefox, Edge, Safari, and Opera; add-ins for Microsoft Word and Google Docs; integrations with LibreOffice and Thunderbird; standalone desktop apps for Windows and macOS; and a REST API for developers building custom workflows. The open-source core, written in Java under the LGPL licence, can also be self-hosted on your own infrastructure — a genuinely unusual option in this market.

There is a corporate twist worth addressing upfront. In April 2023, LanguageTooler GmbH was acquired by Learneo, Inc., a US-based company headquartered in Redwood City, California. Learneo also owns QuillBot, Scribbr, and Course Hero. The product team remains in Germany, and text processing still happens on EU servers, but the data controller is now an American entity. That distinction matters for compliance-conscious organisations, and we will come back to it.

Key Features

Multilingual Grammar and Style Checking

This is LanguageTool's headline strength. Where Grammarly is English-first with limited support for a handful of other languages, LanguageTool offers deep rule coverage across German, French, Spanish, Portuguese, Dutch, Polish, Catalan, and dozens more. For teams operating across European markets, or for individuals who write professionally in multiple languages, there is nothing else in this class that comes close.

AI-Powered Suggestions

Beyond traditional rule-based checking, LanguageTool uses neural network models to detect context-sensitive errors — words that are correctly spelled but wrong in context, awkward phrasing, and stylistic issues. Premium users get advanced style and tone suggestions, plus unlimited text rephrasing. The AI layer has improved significantly in recent years, though it still trails Grammarly for English-specific nuance.

Open-Source Core

The entire LanguageTool engine is open-source under the LGPL licence. You can inspect the code, contribute rules for your language, or run it entirely on your own servers. For organisations with strict data sovereignty requirements — legal firms, government agencies, healthcare providers — this is transformative. No text needs to leave your network, ever.

Integration Breadth

LanguageTool covers most of the places where people actually write. The browser extensions work across Gmail, WordPress, social media, and any web-based text field. The Microsoft Word add-in and Google Docs integration handle document workflows. LibreOffice and Thunderbird support caters to the open-source office stack. A standalone web editor rounds out the consumer experience.

Developer API

The REST API allows developers to integrate grammar and style checking into their own applications. The public API has rate limits (20 requests per minute per IP), while premium and enterprise tiers offer higher throughput for production use. Documentation is adequate but could be more transparent on pricing and limits.

Pricing

LanguageTool runs a straightforward freemium model. The free tier is genuinely useful — basic grammar, spelling, and punctuation checks work across all platforms with a character limit per check. It is one of the more generous free tiers in the writing tools category.

Premium Individual costs EUR 19.90 per month, or EUR 59.90 per year — roughly EUR 5 per month on an annual plan. That undercuts Grammarly significantly on a yearly basis and includes advanced grammar and style checks, unlimited rephrasing, and support for texts up to 100,000 characters.

Team pricing runs at EUR 56.90 per user per year for groups of 2 to 20, billed annually only. This provides centralised licence management and all Premium features, but lacks the collaborative editing and admin dashboards that competitors like Grammarly Business offer.

Enterprise and API pricing is custom. Contact their sales team at sales@languagetoolplus.com for quotes. This tier includes dedicated account management, custom integration support, and a Data Processing Agreement.

EU Compliance & Privacy

This is where the story gets nuanced. On the surface, LanguageTool looks like a strong EU compliance choice: the company was founded in Germany, the operational entity is LanguageTooler GmbH in Potsdam, and all text processing happens on servers in Germany. Texts sent for checking are not stored, and as of December 2024, customer inputs are no longer used to train language models.

But the ownership change complicates things. Since Learneo's acquisition in 2023, the data controller is Learneo, Inc., a US corporation. This means personal data may be transferred outside Germany, with Learneo relying on the EU-US Data Privacy Framework and Standard Contractual Clauses. For many organisations, this is perfectly acceptable — it is the same legal basis that hundreds of US-owned SaaS products operate under in Europe. But it is a meaningful step down from a fully EU-sovereign stack.

The escape hatch is self-hosting. Because LanguageTool's core is open-source, you can run it on your own infrastructure with zero external data flows. No US data controller, no cross-border transfers, no third-party dependencies. For organisations that need the strongest possible compliance posture, this is a genuine advantage that no other major grammar checker can match.

A Data Processing Agreement is available for team and enterprise customers, and LanguageTool processes data in accordance with the GDPR and the German Federal Data Protection Act (BDSG 2018).

Who It's Best For

Multilingual European teams writing in multiple languages across the continent. No competitor matches LanguageTool's depth of coverage in German, French, Dutch, Polish, Spanish, and beyond.

Privacy-conscious organisations that want the option to self-host their grammar checking infrastructure. The open-source deployment eliminates data transfer concerns entirely.

Cost-sensitive users and teams who want premium grammar checking without Grammarly's price tag. At EUR 59.90 per year, the individual plan is substantially cheaper.

Developers and integrators who need a grammar API to embed in their own applications, particularly for multilingual content processing.

Open-source advocates in government, education, and NGOs who prefer or require open-source tooling as a matter of policy.

The Verdict

LanguageTool occupies a unique position. It is the only grammar checker that combines genuine multilingual depth, an open-source core, EU-based data processing, and competitive pricing. For anyone who writes in languages other than English, or who needs the self-hosting option for compliance reasons, it is the obvious choice.

The US ownership through Learneo is a real consideration for organisations pursuing full EU data sovereignty, though the self-hosting option largely neutralises that concern. English-specific AI suggestions remain a step behind Grammarly's, and the team collaboration features are minimal. But at a fraction of Grammarly's price, with vastly superior multilingual support and a transparent open-source foundation, LanguageTool is a strong pick for European users who want writing assistance built on their terms.

Frequently Asked Questions

Is LanguageTool GDPR compliant?

Yes, in practice. Text processing happens on EU servers in Germany, and no customer text is used for model training. However, the data controller is now US-based Learneo, Inc., which uses Standard Contractual Clauses for EU-US data transfers. For full sovereignty, self-host the open-source version on your own infrastructure.

How does LanguageTool compare to Grammarly?

LanguageTool wins on multilingual support (30+ languages vs English-focused), price (roughly half on annual plans), open-source availability, and EU data processing. Grammarly wins on English-specific AI suggestions, team collaboration features, and overall polish of the writing experience. The right choice depends on whether you prioritise multilingual coverage or English depth.

Can I self-host LanguageTool?

Yes. The core engine is open-source under the LGPL licence. You can run a LanguageTool server on your own infrastructure using the Java-based server, with complete control over data flows. Community and enterprise rule sets are available, and the self-hosted version receives regular updates.

Who owns LanguageTool now?

LanguageTooler GmbH, headquartered in Potsdam, Germany, was acquired by Learneo, Inc. (Redwood City, California) in April 2023. Learneo also owns QuillBot, Scribbr, and Course Hero. The LanguageTool product team continues to operate from Germany.

Does the free tier require an account?

The browser extension and web editor work with basic functionality without an account. Creating a free account unlocks a personal dictionary and additional features. Premium features require a paid subscription.