LanguageTool

LanguageTool is an open-source proofreading and writing assistant that detects spelling, grammar, punctuation, and style issues in many languages. It can be used through its editor and integrations, and it can also be run as a server for programmatic checking.

Key Features

• Checks grammar, spelling, punctuation, casing, and style issues beyond basic spellcheck
• Supports 30+ languages and dialects with automatic language detection
• HTTP server mode with a REST API for integrating into apps and workflows
• “Picky”/more advanced rule checking for stricter style and typography suggestions
• Custom dictionaries and the ability to add words and exceptions
• Rule-based NLP approach with extensible language-specific rules

Use Cases

• Self-hosted text checking API for internal tools, CMSes, or document pipelines
• Quality control for multilingual content teams and editorial workflows
• Integrations in enterprise environments where text must remain on controlled infrastructure

Limitations and Considerations

• Many advanced suggestions and some AI-based capabilities are tied to proprietary/hosted offerings rather than the open-source core
• Accuracy and coverage can vary by language depending on available rules and maintainership

LanguageTool is a strong option for organizations and individuals who need a privacy-friendly, multilingual grammar and style checker. Its server mode and API make it especially useful when you want to integrate proofreading into products or internal systems.