LanguageTool

Detects grammatical errors including incorrect word order, wrong verb tense, subject-verb agreement violations, and syntactic mistakes across 30+ languages. Uses rule-based pattern matching combined with statistical language models to identify deviations from correct grammar in real-time as users type. The extension parses text incrementally without storing it locally, sending only flagged segments to backend servers for verification when paraphrasing or advanced checks are requested.

Identifies misspelled words and orthographic errors by comparing input text against language-specific dictionaries and statistical models. Users can add custom words to a personal dictionary to prevent false positives on domain-specific terminology, brand names, or non-standard spellings. The extension maintains per-user dictionary state and applies it during spell-checking without uploading the dictionary to servers.

Provides a standalone web application at languagetool.org where users can paste text and receive comprehensive grammar, spelling, punctuation, and style checking without installing a browser extension. The web editor supports all LanguageTool checking features including paraphrasing (Premium), Style Guides, and statistics. Users can check text up to 150,000 characters (Premium limit) and export results. The web editor serves as an alternative to browser extension for users who prefer not to install extensions or need checking in non-browser contexts.

Allows organizations to deploy LanguageTool server on their own infrastructure for on-premises checking without sending text to external servers. Users can configure their browser extension or web editor to connect to a self-hosted LanguageTool server instead of the default cloud service. This enables organizations to maintain full data privacy and control while using LanguageTool's checking capabilities. Self-hosting requires technical infrastructure management and server maintenance.

Detects punctuation mistakes (missing commas, incorrect quotation marks, spacing around punctuation) and typography issues (double spaces, inconsistent dash usage, improper ellipsis formatting). Premium tier includes 'Picky Mode' that enables advanced punctuation and typography checking beyond basic rules. Style Guide feature allows users to define custom punctuation and typography rules (e.g., enforcing Oxford commas, specific quotation mark styles) that are applied during checking and can be shared across teams.

Generates alternative phrasings of sentences and paragraphs using neural language models, with options to adjust tone (formal, casual, professional) and style (more concise, more fluid, simpler language). Users select text and request paraphrases; the extension sends the selected text to backend servers where a transformer-based model generates alternatives. Multiple paraphrase options are returned, allowing users to choose the best fit for their context. This feature is Premium-only and powered by undisclosed AI models.

Automatically detects the language of input text across 30+ supported languages and applies language-specific grammar, spelling, and punctuation rules. Detection occurs on-demand as text is entered; users can manually override detected language if needed. The extension maintains separate rule sets for each language and applies the appropriate set based on detected language, enabling seamless multilingual writing without manual language switching.

Renders error highlights and suggestion popups directly within browser text fields and rich text editors without modifying page DOM structure. Uses browser extension content script injection to detect text field changes, apply error detection, and render underlines and suggestion UI overlays. Suggestions are presented in a context menu or popup that appears on hover/click of highlighted errors, allowing users to accept corrections or dismiss false positives without leaving the text field.

Extends grammar and style checking to native desktop applications including Microsoft Office (Word, Outlook), Apple applications (Pages, Mail, Notes, Messages), and other text editors (WordPad, Notepad). Integration mechanism is platform-specific (likely using OS-level accessibility APIs or application-specific plugins) and allows error detection and suggestions within native application UIs without browser involvement. Desktop integration is available on Windows and macOS.

Allows users to define custom grammar, punctuation, and style rules through a Style Guide interface, specifying rule conditions and corrections. Style Guides can be created at individual or team level; team Style Guides are shared across all team members and applied during checking for all members. Rules are stored server-side and applied during text analysis without requiring local configuration. Team plans enable collaborative rule management and enforcement across organizations.

Maintains a shared team dictionary of custom terminology, brand names, and domain-specific words that should not be flagged as spelling errors. Team members can add words to the shared dictionary; additions are immediately available to all team members. The team dictionary is stored server-side and applied during spell-checking for all team members, preventing false positives on organization-specific terminology without requiring manual dictionary entries per user.

Tracks user writing metrics including total words written, error counts by category, improvement trends over time, and error frequency patterns. Statistics are aggregated server-side and presented in a dashboard showing productivity metrics and error reduction over time. Users can view historical error patterns to identify recurring mistakes and track writing improvement. Statistics tracking is a Premium feature and requires server-side data collection.