In simple English
Harper checks your writing for spelling and grammar errors. It runs entirely on your own device. Your words never travel to an outside server. It costs nothing to use and has no subscription fees. It works quickly without slowing down your computer.
What it is
Harper is an open-source grammar checker written in the Rust programming language (a system for writing fast programs that use very little memory). It checks English text instantly inside your text editor or browser.
What it is good for
Writers and developers who want privacy for their drafts and notes. It removes the need for expensive online writing assistants that require an internet connection.
Stars17k
LicenceApache-2.0
Latestv2.13.0 (2026-10-16)checked 24 Oct 2026
Last code change2026-10-23
Written inRust
Setup effort
3 / 5
Payoff
4 / 5
Good
- Runs completely offline to keep all your personal writing private.
- Checks long documents in milliseconds instead of several seconds.
- Uses very little memory compared to traditional grammar tools.
Watch for
- Only checks English text at the moment.
- Requires some technical steps to set up inside your text editor.
- Relies on plugins made by the community to connect with different programs.
Replaces
Grammarly
Works well with
Obsidian
Similar repositories
- languagetool-org/languagetool15k stars
LanguageTool checks grammar in many languages, but it needs significantly more memory to run.
Install
cargo install harper-ls