Harper review
A private, free English grammar checker for writers, developers, and technical teams.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
Harper is a free, open-source grammar checker for writers, developers, and technical teams. It checks spelling, capitalization, grammar, punctuation, and phrasing locally on the device. The product supports English dialect selection, including British, American, Canadian, Australian, and Indian English. Its privacy-focused design suits people who want offline analysis without creating an account, while its developer integrations make it relevant for technical writing and code-adjacent workflows.
Harper’s ecosystem spans Chrome and Firefox extensions, Microsoft Edge, VS Code, Cursor, Obsidian, WordPress, Neovim, Zed, Helix, Emacs, Sublime Text, and macOS apps. Developers can also work with its Language Server Protocol integration, JavaScript library, and Rust crate. User, workspace, and file-local dictionaries provide control over terminology, while custom grammar rules through Weir support specialized writing conventions. The platform coverage includes web, Windows, macOS, Linux, browser extensions, and an API, although system-wide macOS text-field integration is specific to macOS.
The published Free plan costs $0 USD and includes local grammar checking, open-source licensing under Apache-2.0, and no account or credit card requirement. There are no paid tiers described, so the product is straightforward to evaluate and adopt without a subscription decision. Harper is a strong choice for privacy-focused English users, developers, and technical teams that value local processing, customization, and editor support. It is less suitable for users seeking broad multilingual coverage, AI-based writing assistance, or mobile-focused checking.
Harper pros and cons
- Where it wins
- Free, open-source checking with no account or credit card required
- Offline, on-device analysis for spelling, grammar, and punctuation
- Broad editor, browser, desktop, and developer integrations
- Where it doesn't
- Coverage is centered on English and its dialects
- It does not include AI features
- Desktop text-field integration is specific to macOS
Harper fact sheet, pricing and score →
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