Harper

Harper is an offline, privacy-first English grammar checker written primarily in Rust. It analyzes writing locally, avoiding the latency and data exposure associated with cloud-only services. The engine is designed to lint documents in milliseconds while using a small memory footprint. It can run through WebAssembly in browsers and applications or through native command-line and language-server components. Official integrations support editors and tools including Visual Studio Code, Neovim, Helix, Emacs, Zed, and Obsidian. Its modular repository also contains parsers for formats such as HTML, TeX, Typst, AsciiDoc, and source-code comments. The core currently focuses on English but is designed to be extended to additional languages.