At a Glance:
Harper is an open-source, local-first English grammar checker designed as a fast, lightweight alternative to Grammarly and LanguageTool, capable of linting documents in milliseconds and running entirely via WebAssembly.
Overview:
Harper is an English grammar checking engine built to address performance, cost, and privacy issues found in competing tools. It focuses on being fast, taking milliseconds to lint documents, and remaining lightweight, with a memory footprint less than 1/50th of LanguageTool. Harper operates completely locally, meaning text is never sent to external servers. The project is intentionally minimal, fitting the creator’s specific workflow needs, and is compact enough to run in environments supporting WebAssembly. It is primarily intended for users who need immediate, private grammar feedback within supported text editors.
Key Decision Points:
Local-first execution: Harper runs entirely on the user's machine, avoiding network round trips and ensuring text never leaves the local environment.
Extremely low resource usage: It uses a fraction of LanguageTool’s memory and is designed to be small enough for WebAssembly contexts.
English-only with extensible core: Current language support is limited to English, but the architecture allows, and contributions are welcomed, for adding other languages.
Editor integration model: Harper is available as an integration for specific editors, including Visual Studio Code, Neovim, Helix, Emacs, and Zed, rather than a standalone application.
Core Features:
Millisecond-scale document linting: Designed to process checks with near-instant speed, treating significant performance issues as bugs.
Private, local processing: All grammar checking is performed on-device without sending user writing to remote servers.
WebAssembly compatibility: The engine is small enough to be loaded and run in WebAssembly-based environments.
Use Cases:
Developers and technical writers who want an offline, integrated grammar checker within editors like Neovim, Helix, or Visual Studio Code.
Users seeking an alternative to cloud-based tools for privacy reasons, ensuring written text is processed locally rather than transmitted externally.
Users working on resource-constrained devices where memory-heavy grammar checkers are impractical.
Open-Source Alternative Value:
As an open-source project, Harper offers a transparent and locally-controllable alternative to proprietary grammar services like Grammarly and memory-intensive tools like LanguageTool. Its value proposition is grounded in speed, privacy, and efficiency, processing documents entirely on-device with minimal resource consumption. The codebase’s extensible core also opens the possibility for community members to contribute support for languages beyond English, allowing the tool to evolve beyond its original scope through direct contributions.
