Harper

Harper is an English grammar checker written by someone tired of the alternatives. Paid cloud checkers send everything you write to a remote server and add a network round trip to every revision, while heavyweight local tools ask for gigabytes of memory and a sixteen gigabyte n-gram dataset. Harper lints a document in milliseconds and uses less than a fiftieth of the memory LanguageTool needs.

Everything stays on your machine, and the core is small enough to ship as WebAssembly, so the same checker can run inside a browser. The project treats slow linting as a defect and asks people to file significant performance problems as bugs.

Harper reaches writers through several front ends rather than one application.

• harper-ls: a language server that plugs the checker into Visual Studio Code, Neovim, Helix, Emacs and Zed.
• harper.js: a JavaScript package for embedding grammar checking in web pages and applications.
• Obsidian support: documented integration for checking notes without leaving the editor.
• Nothing leaves the device: no text is sent to a third party for analysis, so private drafts stay private.
• English only for now: the core is extensible to other languages, and contributions adding them are welcome.

The project suits anyone who drafts prose inside an editor rather than a web application, and who would rather not trade privacy or memory for correction. Documentation covers each editor integration, and the contribution guide is the starting point for fixes and for language support beyond English.