Harper

Harper is a private, open-source grammar checker that runs on-device and provides real-time grammar, spelling, capitalization, and phrasing suggestions.It ships as a language server and developer libraries for integration into web apps and tooling.

Editor integrations include VS Code, Neovim, Zed, Emacs, Sublime, and Obsidian, while browser and desktop coverage includes Chrome and Firefox extensions plus a macOS desktop app and a WordPress block-editor plugin.

All checks execute locally with no cloud round-trips or telemetry, preserving user text privacy and enabling inline suggestions without server delays.Harper supports multiple English dialects (US, UK, Canadian, Australian, Indian) and offers programming-language-aware checks via editor integrations.

The project is available under the Apache‑2.0 license on GitHub with documentation, rule reference, and contribution guides for customization and extension.

Key Features

• Real-time grammar, spelling, capitalization, and phrasing suggestions
• Runs on-device; all checks execute locally with no cloud round-trips or telemetry
• Provides a language server and developer libraries (harper-ls, harper.js, harper-core, Rust crate) for integration
• Editor, browser, and desktop integrations (VS Code, Neovim, Zed, Emacs, Sublime, Obsidian; Chrome/Firefox extensions; macOS app; WordPress plugin)
• Open-source (Apache-2.0) on GitHub with documentation, rule reference, and contribution guides for customization and extension

Use Cases

• Integrate Harper via its language-server and developer libraries into your team's IDEs and editors to get real-time, code-aware grammar, spelling and phrasing suggestions in pull requests and commits while preserving privacy with local-only checks and support for multiple English dialects
• Embed Harper on privacy-sensitive devices and apps to provide on-device grammar, capitalization and style corrections for writers, journalists and legal teams without sending text to the cloud, leveraging the open-source library for easy customization
• Add Harper to your publishing and CI workflows to automatically enforce dialect-specific style guides and perform automated proofreading before release, using editor integrations and on-device checks to keep content private and reproducible

Who is it for?

• Software developers
• Programmers
• Technical writers
• Content creators
• Open-source contributors