LanguageTool

LanguageTool began as an academic research project in 2003, created by Daniel Naber as part of his diploma thesis at the University of Bielefeld in Germany. Over two decades later, it has evolved into one of the most comprehensive grammar, style, and spell checking platforms available, supporting more than 30 languages and serving millions of users worldwide. The company behind it, languagetoolplus GmbH, is headquartered in Potsdam, Germany, and operates as a privacy-first alternative to US-based writing assistants like Grammarly, ProWritingAid, and Microsoft Editor.

What distinguishes LanguageTool in 2026 is its unique combination of open-source transparency, genuine multilingual capability, and European data governance. While Grammarly dominates the English-language market, LanguageTool has carved out a strong position by excelling where competitors fall short: non-English languages, privacy, and organizational self-hosting. The platform checks grammar, spelling, punctuation, and style across languages including German, French, Spanish, Dutch, Portuguese, Polish, Russian, and many more -- with rules developed and maintained by native-speaking linguists rather than just machine learning models.

Multilingual Grammar Checking at Its Core

LanguageTool's greatest strength is its deep, linguistically-informed support for over 30 languages. Unlike competitors that primarily focus on English and offer limited support for other languages, LanguageTool treats each language as a first-class citizen. The rule sets for major European languages like German, French, Spanish, and Dutch are particularly robust, containing thousands of language-specific grammar rules, style suggestions, and regional variant awareness (e.g., distinguishing between European Portuguese and Brazilian Portuguese, or Swiss German and standard German).

The grammar checking engine combines rule-based approaches (handcrafted by linguists) with neural network models trained on language-specific corpora. This hybrid approach catches errors that pure statistical models miss, particularly in morphologically complex languages like German (where compound word formation and case agreement require deep linguistic knowledge) or French (with its complex conjugation and agreement rules). For organizations operating across European markets, this multilingual depth is a decisive advantage over Grammarly, which only supports English, German, French, Spanish, and Portuguese with varying degrees of depth.

AI-Powered Writing Assistance

In recent years, LanguageTool has expanded beyond traditional grammar checking into AI-powered writing assistance. The Premium tier includes paraphrasing capabilities that suggest alternative ways to express sentences, tone adjustment features that help writers adapt their text for different audiences, and style improvements that go beyond grammar correctness to enhance clarity and readability. These AI features are powered by large language models trained with privacy in mind -- text is processed but not stored for model training, a critical distinction from some competitors.

The AI writing suggestions are context-aware, meaning they consider the surrounding text and the overall document purpose when making recommendations. For professional users, this means receiving suggestions appropriate for business communication rather than casual writing, and vice versa. The system also detects and adapts to the specific language variant being used, ensuring suggestions are culturally appropriate for the target audience.

Browser Extensions and Desktop Integration

LanguageTool is available as browser extensions for Chrome, Firefox, Edge, Safari, and Opera, checking text as you type in virtually any web-based text field -- email clients, social media, content management systems, and web-based editors. The extensions are lightweight and activate automatically, underlining errors with colored highlights and offering one-click corrections. The experience is comparable to Grammarly's browser extension, with the added advantage of multilingual support and privacy-focused data handling.

Beyond browsers, LanguageTool integrates with Microsoft Word (via add-in), Google Docs, LibreOffice, Apple Mail, and Thunderbird. A standalone desktop application for Windows, macOS, and Linux provides system-wide checking that works in any application. The desktop app includes the option for local text processing (Premium feature), where all grammar checking happens on-device without sending text to external servers -- a feature unavailable in Grammarly or most competitors.

API for Developers and Businesses

LanguageTool provides a REST API that developers can integrate into their own applications, content management systems, or publishing workflows. The API accepts text and returns detected errors with suggested corrections, error categories, and position information. It supports all 30+ languages and can process both plain text and annotated markup. Rate limits vary by plan: the free tier allows limited requests, while paid API plans support high-volume usage for production applications.

For businesses building content platforms, customer support tools, or document management systems, the LanguageTool API offers a way to embed professional-grade grammar checking without building the capability from scratch. The API is used by publishers, legal technology companies, and educational platforms across Europe. Self-hosted API deployments are also available for organizations that need to process text entirely within their own infrastructure.

Self-Hosting for Maximum Privacy

One of LanguageTool's most distinctive features is the ability to self-host the entire grammar checking engine on your own servers. The open-source core can be deployed as a Java application or Docker container, providing the same checking capabilities without any text leaving your network. This is particularly valuable for organizations handling sensitive documents -- law firms, government agencies, healthcare institutions, and financial services companies that cannot risk sending confidential text to third-party servers.

The self-hosted version includes the rule-based checking engine and can be extended with n-gram data for enhanced error detection. Premium features like the AI-powered suggestions require the cloud service, but the core grammar and style checking works fully offline. Organizations can deploy the server internally and configure it for specific language requirements, custom dictionaries, and organizational terminology.

Open Source Foundation and Community

LanguageTool's core engine is released under the GNU Lesser General Public License (LGPL), making it one of the few professional-grade grammar checkers with a fully open-source foundation. The source code is hosted on GitHub, where hundreds of contributors have added language rules, fixed bugs, and extended functionality. The open-source model means security researchers can audit exactly how text is processed, and organizations can verify that no data is being exfiltrated or misused.

The community contributes language rules across dozens of languages, including many that are underserved by commercial tools (Catalan, Galician, Breton, Asturian, and others). This community-driven approach to language support ensures that LanguageTool covers linguistic diversity that no commercial company would invest in purely for profit. The open-source nature also means that the tool can be adapted for specialized use cases -- academic institutions, for example, have created custom rule sets for scientific writing standards.

Privacy and GDPR Compliance

As a German company, languagetoolplus GmbH operates under the strictest interpretation of GDPR. The company's privacy practices go beyond legal compliance: text submitted for checking is processed in real time and not permanently stored, no account is required for the free version, and Premium users can opt for fully local text processing. The company publishes a detailed privacy policy and has been transparent about its data handling practices in a way that builds trust with privacy-conscious users.

For European organizations evaluating writing tools, LanguageTool's German data governance provides a clear advantage over Grammarly (US-based, owned by a Ukrainian-American company operating from San Francisco) and Microsoft Editor (US-based, subject to the CLOUD Act). When employees use writing assistants for business communication, the text being checked often contains sensitive information -- business strategies, client names, financial data, legal documents. Having this text processed by a German company under GDPR, with the option for on-premise processing, addresses legitimate data protection concerns.

Pricing Tiers and Value

LanguageTool offers a generous free tier that includes basic grammar and spelling checking with a 10,000-character limit per check. The Premium plan (from approximately EUR 4.99/month when billed annually) removes character limits, adds advanced style and punctuation rules, AI-powered suggestions, personal dictionaries, and priority support. A Teams plan extends Premium features with centralized administration, shared dictionaries, and usage analytics for organizations. Enterprise pricing with self-hosting options and dedicated support is available by arrangement.

Compared to Grammarly Premium (around $12/month annually), LanguageTool offers comparable core functionality at a lower price point, with the significant additions of genuine multilingual support and privacy options. For multilingual European professionals, the value proposition is particularly strong -- a single LanguageTool Premium subscription covers all 30+ languages, while Grammarly offers limited support outside English.

Who Should Choose LanguageTool

LanguageTool is the strongest choice for multilingual writers and organizations that need grammar checking across European languages, privacy-conscious users and businesses that want GDPR-compliant text processing with the option for local or self-hosted checking, and open-source advocates who value transparency and community-driven development. English-only writers who want the most advanced AI writing features may still find Grammarly's English-specific capabilities more polished, but for anyone writing in multiple languages or prioritizing data sovereignty, LanguageTool is the clear European leader in its category.