LanguageTool
Open-source grammar checker supporting 31 languages. Self-hostable. The privacy-first alternative to Grammarly — run it locally and no text leaves your machine.
What should journalists know about LanguageTool?
LanguageTool is the only major grammar checker with an open-source core. Started in 2003 as Daniel Naber's diploma thesis at Bielefeld University in Germany. Grew into a community-maintained project with volunteer linguists contributing rules for 31 languages. In 2017, Naber and Christopher Blum co-founded LanguageTooler GmbH to commercialize it. In April 2023, Learneo Inc. (Redwood City, CA) acquired the company. Learneo also owns QuillBot, Course Hero, Scribbr, and CliffsNotes. The core value proposition for journalists is self-hosting. Download the open-source server, run it on your laptop or newsroom infrastructure, and every grammar check happens locally. No text transmitted. No third-party retention. No training pipeline. This is the only grammar tool that offers true air-gapped operation. The self-hosted version lacks some premium AI features but covers grammar, spelling, and style rules comprehensively. If you use the cloud service (languagetool.org), text is sent to LanguageTool servers for processing. As of December 2024, LanguageTool no longer uses input text to train its language models. Text submitted for checking is not stored, with narrow exceptions: if you submit explicit feedback on a false positive, accept a typo correction, or toggle a rule. No full IP addresses are stored. The catch: official browser extensions are closed-source. The open-source core is the server component. For full transparency, use the self-hosted server with the LibreOffice/OpenOffice plugin (which is open-source) or connect via the API. The Chrome and Firefox extensions are proprietary and their behavior cannot be independently audited. Grammar checking quality is strong for English and German, good for French, Spanish, Dutch, Polish, and Portuguese. Thinner for less-common languages. The AI rewriting features (paraphrasing, style suggestions) are cloud-only and not available in the self-hosted version. For pure grammar and style checking without AI features, the self-hosted version is fully capable.
Privacy-first grammar checking. Multilingual newsrooms (31 languages). Self-hosted deployments where no text can leave the network. Journalists on tight budgets — the free tier and open-source self-hosting cost nothing. LibreOffice users get a native open-source integration.
Writers who need advanced AI rewriting features locally (cloud-only). Heavy Grammarly users expecting identical feature depth in English — Grammarly's AI suggestions are more extensive. Anyone needing a fully open-source browser extension (official extensions are closed-source).
Security & Privacy
Data is scrambled while being sent to their servers
Data is scrambled when stored on their servers
Where servers are located — affects which governments can request your data
Privacy policy summary
Cloud service: text sent for checking is not stored. Exceptions: explicit user feedback on false positives, accepted typo corrections, and rule toggles. No full IP addresses stored. As of December 2024, LanguageTool does not use input text to train language models. Non-content usage data (feature usage, error counts) is collected. Data controller is Learneo Inc. (California). Personal data may be processed in US, Germany, Netherlands, Israel, India, and Canada. GDPR and BDSG 2018 apply. Self-hosted: no data leaves your machine. No telemetry. No account required. The open-source server processes everything locally.
How to protect yourself:
For maximum privacy, self-host the open-source server: download from GitHub (languagetool-org/languagetool), run via Docker or Java, connect via API or LibreOffice plugin. No text leaves your machine. For the cloud service, no special opt-out is needed — text is not stored or used for training as of December 2024. Use the LibreOffice/OpenOffice plugin (open-source) rather than the closed-source browser extensions if auditability matters. Disable the browser extension on sensitive sites if using the cloud version.
Self-hosted deployment is the gold standard for privacy: open-source core (LGPL 2.1), local processing, no network dependencies, no account required. Cloud service also has a clean posture — text is not stored or used for training, no IP logging. The main caveats are the closed-source browser extensions (cannot be independently audited) and the Learneo acquisition shifting data controllership to a US entity. For maximum trust, self-host the server and use the open-source LibreOffice plugin. The cloud service is adequate for non-sensitive work.
Who Owns This
Known issues
Closed-source browser extensions: All official LanguageTool browser extensions (Chrome, Firefox, Edge, Safari) are closed-source. The team has confirmed no plans to open-source them again. Only the LibreOffice and OpenOffice plugins remain open-source. This limits independent auditability of the most common client. Learneo acquisition: The April 2023 acquisition moved data controllership from a small German company to a US-based education technology conglomerate. Privacy policy now references data processing across six countries. The December 2024 policy update (no training on user text) was a positive step, but policies can change under new ownership. Self-hosted limitations: The open-source server handles grammar, spelling, and style rules but does not include AI-powered paraphrasing or advanced rewriting features. Premium cloud features are not available locally. Language depth varies: English and German have the deepest rule sets. Other languages rely on volunteer-maintained rules and may miss errors that Grammarly or dedicated single-language tools would catch. Maintenance transition: In March 2025, original creator Daniel Naber handed maintenance of the open-source project to Stefan Viol at LanguageTooler GmbH. Long-term community health depends on continued investment by Learneo.
Pricing
Free (basic checks, 10,000 character limit per field, 3 AI rephrases/day). Premium Individual: $4.99/month (annual) or $19.90/month (monthly). Teams: $9.49/month per user (annual, 2+ users). Self-hosted: free (open-source core under LGPL 2.1, run your own server via Docker or Java).
This is an editorial assessment based on publicly available information as of 2026-04-03, using our published methodology. Independent security review is pending. Security posture can change at any time. This is not a guarantee of safety.
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