Harper is a grammar checker that runs offline and prioritizes privacy by processing text locally without sending data to external servers.
The tool addresses the limitations of existing grammar checkers. Grammarly sends all writing to its servers, raising privacy concerns, and its suggestions often lack context. LanguageTool requires gigabytes of RAM and a large n-gram dataset download, making it memory-intensive and slow. Harper solves these problems by performing grammar checking in milliseconds while using a fraction of LanguageTool's memory footprint. It achieves this efficiency through a Rust implementation that is compact enough to run as WebAssembly in browsers, enabling integration into web-based editors and extensions.
Harper currently supports English only, though the architecture is designed to be extensible for other languages. The tool integrates with multiple editors including Visual Studio Code, Neovim, Helix, Emacs, and Zed through a language server implementation, and works with Obsidian. It is also available as a Chrome extension and as a JavaScript library for web applications. Anyone choosing Harper should expect a focused, privacy-respecting alternative to cloud-based checkers, particularly suited for developers and writers who want local processing and minimal resource consumption.
The project treats performance regressions as bugs and welcomes contributions addressing speed issues. Development activity shows engagement with the community through multiple editor integrations and active maintenance of documentation across different platforms. The tool has been built to handle real-world writing workflows efficiently, with the team prioritizing responsiveness as a core design principle.
