Check English grammar locally without sending text to a server
It catches typos and grammar errors in your documents without sending them to an external server. This offline grammar checker processes everything on your computer. You receive feedback in milliseconds without network latency, which speeds up the editing process.
Privacy and Speed
Harper processes all user-written text locally, so personal information does not leak externally. The problem of slow editing due to network round-trip time is eliminated. Document checks are processed in milliseconds, allowing for real-time feedback. It performs grammar checks at a consistent speed regardless of internet connection status.
Lightweight Resource Usage
Harper uses less than one-fiftieth of the memory compared to LanguageTool. LanguageTool requires downloading an n-gram dataset of approximately 16GB and often takes several seconds to check medium-sized documents. Harper is lightweight enough to be loaded as WebAssembly, allowing it to run lightly in browser extensions or various development environments. Long check times are treated as bugs, and performance issues are actively managed.
Supported Environments and Extensibility
Currently, Harper only supports English grammar checking. However, the core structure is designed to be extensible, and contributions for other language support are welcome. It can be used in major code editors such as Visual Studio Code, Neovim, Helix, Emacs, and Zed, as well as in Obsidian. It can also be easily integrated into developer tools and web applications through harper-ls and harper.js.
Suitable for English Writing Environments
Harper is suitable for English users or developers who write in English. If you primarily use other languages, it is not available in the current version, so you must verify this point. Since all processing occurs offline, it is particularly useful in environments that prioritize privacy. Before installation, it is recommended to check the list of supported editors and the harper-ls documentation to ensure compatibility with your working environment.