Best open-source alternatives to Grammarly

Harper is an English grammar checker built to provide context-aware suggestions while remaining fast and private. The README positions it as an alternative to cloud-based or resource-heavy competitors, emphasizing that linting happens in milliseconds and with a much smaller memory footprint than LanguageTool. The project appears aimed at writers and developers who want grammar assistance inside their tools rather than a standalone web app. It supports English today and is designed to be extensible to other languages. The README also highlights integration paths through a language server, editor plugins for several popular editors, and a JavaScript/WebAssembly form factor for embedding in web contexts.