Automattic/harper ? reverse-engineered prompt

Build me Harper, an offline, privacy first English grammar checker that feels fast and smart, not intrusive. I want it to check writing locally on the device, give clear suggestions, and work in a way that can be used from the command line, in editors through a language server, and in a small web demo or browser friendly version. It should be lightweight, quick to run, and only focus on English for now.

Make the experience simple, polished, and easy to use, with obvious error highlighting and helpful fixes. If you need to, look up current docs online for the best way to wire up the integrations, but keep everything local and private. I’d also like the project organized cleanly so the core grammar engine can be shared across the different interfaces without duplicating logic.