LanguageTool

Detects grammar errors and spelling mistakes as users type in any web form field (email, comments, posts, chat) by injecting content scripts into the DOM and analyzing text against a rule-based engine with 20,000+ checks for premium languages. The extension works inline without storing text, providing instant visual feedback with underlined errors and correction suggestions directly in the text field.

Generates alternative phrasings of sentences using a state-of-the-art AI model with user-selectable tone options (formal, fluid, shorter variants). Users highlight text and trigger paraphrasing to receive multiple rewrite suggestions that maintain semantic meaning while adjusting formality, conciseness, or flow. This feature is premium-only and processes text through cloud-based AI inference.

LanguageTool is available as open-source software that organizations can deploy on their own servers, enabling on-premise checking without sending text to LanguageTool's cloud infrastructure. Self-hosted deployments support the same grammar, spelling, and style checking features as the cloud service, with full control over data retention and processing. Organizations can integrate the self-hosted server with custom applications via HTTP API or use it as a backend for custom browser extensions.

Team tier enables organizations to invite and manage up to 200 users under a single team account, with shared style guides, shared dictionaries, and unified billing. Team administrators can manage user access, configure team-wide writing standards, and track team writing statistics. All team members inherit premium features (paraphrasing, picky mode, enhanced checking) without individual subscriptions. Team resources (style guides, dictionaries) are synchronized across all team members.

Automatically detects the language of input text across 30+ supported languages and dialects, then applies language-specific grammar, spelling, and style rules without requiring manual language selection. Detection occurs on-the-fly as users type, with fallback to manual language selection if auto-detection fails. Premium tier includes enhanced 20,000+ check suite for 7 languages (English, German, French, Spanish, Dutch, Polish, Portuguese).

Allows users (premium tier) to define custom writing rules and terminology preferences that are enforced across all text checking. Style guides can specify preferred phrasings, terminology consistency, tone guidelines, and custom rules that override default LanguageTool checks. Team tier enables shared style guides across up to 200 users, enforcing organizational writing standards consistently. Rules are stored server-side and applied during text analysis.

Maintains user-specific and team-specific dictionaries of custom terms, technical jargon, and proper nouns that should not be flagged as spelling errors. Users can add words to their personal dictionary during checking, and team tier enables shared dictionaries across all team members. Dictionary entries are stored server-side and applied during spell-checking to prevent false positives on domain-specific terminology.

Premium-only feature that enables 20,000+ additional grammar, style, punctuation, and typography checks beyond the basic rule set. Picky mode applies stricter rules for consistency (e.g., serial comma usage, spacing around punctuation, capitalization patterns) and style preferences (e.g., word choice, redundancy, clichés). Available only for 7 languages (English, German, French, Spanish, Dutch, Polish, Portuguese). Can be toggled on/off in settings to balance between strictness and false positive rate.

Provides a standalone web-based editor (LanguageTool Editor) where users can paste text or type directly for checking without installing browser extensions or desktop applications. The web editor supports the same grammar, spelling, style, and paraphrasing features as the browser extension, with a clean interface for reviewing suggestions and making edits. Useful for checking text on devices where extensions cannot be installed (mobile, restricted environments) or for one-off checks without extension overhead.

Extends LanguageTool checking to native desktop applications including Microsoft Outlook, Word, Pages, Mail, Slack, Notes, and Messages on Windows and macOS. Integration mechanism unknown (likely system-level text input interception or native application plugins), but provides the same real-time detection and suggestions as the browser extension. Desktop integration enables checking in applications where browser extensions cannot operate.

Premium feature that tracks and displays writing metrics including word count, character count, reading time, sentence length distribution, and other analytics. Statistics are aggregated over time to show writing patterns and improvements. Available in premium tier only; free tier does not include analytics. Metrics are stored server-side and accessible via LanguageTool dashboard.

Deploys content scripts into web pages that identify and monitor all text input fields (textarea, contenteditable divs, input[type=text]) and apply grammar/spelling checking in real-time as users type. The extension uses DOM mutation observers to detect new text fields dynamically added to pages and applies checking to them. Content scripts operate in the extension's isolated context to avoid conflicts with page scripts, with claimed zero-storage privacy model for text data.