Harper
Harper is an offline, privacy-first grammar checker developed by Automattic. It is written in Rust for maximum performance and safety. Unlike cloud-based grammar checkers, Harper processes all text locally, ensuring that sensitive content never leaves the user's device. This makes it ideal for environments where data privacy is paramount, such as in enterprise, healthcare, or legal writing. The tool provides real-time grammar and style suggestions, correcting common mistakes like subject-verb agreement, punctuation errors, and word choice. It is designed to be integrated into a variety of applications through its library, command-line interface, or desktop application. Because it is open source, developers can customize rules, add new languages, or embed it directly into their own software. The Rust core ensures low latency and minimal resource usage, making it suitable for use on devices with limited hardware capabilities. Harper’s architecture separates the core engine from language-specific rules, allowing it to support multiple languages with ease. It uses a combination of pattern matching and linguistic rules to detect errors, avoiding the need for large machine learning models that would compromise speed and offline capability. The project is actively maintained by Automattic, the company behind WordPress.com, WooCommerce, and other popular platforms, guaranteeing ongoing development and community support. For end users, Harper offers a desktop application that runs in the background and checks text in any application via accessibility APIs, providing universal grammar checking across macOS. It is also available as a command-line tool for batch processing of text files, and as a library for embedding in editor plugins, writing apps, or CI/CD pipelines for documentation checks. The tool is released under a permissive open-source license, encouraging widespread adoption.
- Category
- Dev Tools
- Pricing
- Open Source
Problem solved
Many writers, developers, and professionals rely on grammar checkers to polish their writing, but popular solutions like Grammarly require sending text to cloud servers, raising privacy concerns and requiring constant internet connectivity. Harper solves this by providing a fully offline grammar checker that runs locally, ensuring privacy and speed. It can be embedded in any application without the user needing to trust a third-party service with their data. This is especially critical for users handling confidential documents, those in regions with unreliable internet, or developers building writing tools that need a lightweight, self-hosted grammar engine.
Use cases
- Integrating grammar checking into a text editor or IDE plugin (e.g., VS Code, Sublime) for real-time feedback.
- Running batch grammar checks on Markdown or documentation files in a CI/CD pipeline before publishing.
- Using the desktop app to check writing across all applications on macOS, such as email clients, note-taking apps, or word processors.
- Embedding Harper in a writing platform (like WordPress) to provide grammar suggestions as users compose posts.
- Processing large amounts of text offline in environments with air-gapped networks, such as government or military.
- Building a custom grammar checker for a non-English language by extending Harper’s rule engine.
Audience
- Developers
- Content Creators
- Business Users
- Enterprise
Pros
- Fully offline and privacy-focused
- High performance due to Rust implementation
- Open source with permissive license
- Easy to integrate via library, CLI, or desktop app
- Backed by Automattic, ensuring long-term support
Cons
- Limited language support (likely English only initially)
- Rule-based approach may not catch as many nuances as AI-driven checkers
- Desktop app currently macOS only
Official website: https://github.com/Automattic/harper
Canonical LambdaBase page: https://www.lambdabase.com/tools/harper