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Harper

The free alternative toGrammarly Pro

🟢 Beginner⏱️ ~5 min to installYou save €12/mo

Harper is Grammarly for English, without the subscription and without sending what you write to the cloud. It underlines spelling, grammar and capitalisation mistakes and clumsy phrasing right where you write: Chrome, Edge, Firefox, VS Code, Obsidian, WordPress, Neovim, Zed, and a macOS app that checks every text field. Everything happens offline, with a memory footprint fifty times smaller than LanguageTool. The project is backed by Automattic, the company behind WordPress. The thing to know before leaving Grammarly: Harper only checks English (American, British, Canadian, Australian, Indian). For your French texts it will do nothing: the core is built for other languages, but none exists yet.

Screenshot of Harper, the free open source alternative to Grammarly Pro
GitHub stars17,323
View on GitHub ↗

Versus Grammarly Pro: the match

  • Price

    Harper

    €0

    Grammarly Pro

    €12 a month billed yearly

  • Where your text goes

    Harper

    Nowhere, everything happens offline

    Grammarly Pro

    To their servers, at every keystroke

  • Languages

    Harper

    English only, five variants

    Grammarly Pro

    English, plus a few languages in beta

Grammarly Pro ↗

How to install it (even from zero)

Nothing to host: it is an extension or an app. The prompt tells you which one to install depending on where you write, and has you check that it corrects.

  1. 1

    Paste this prompt into Claude (Code or Desktop)

    It asks where you write, installs the right extension from the official links and has you test with a sentence full of mistakes:

    Je veux installer Harper (correcteur de grammaire anglais open source, dépôt GitHub Automattic/harper, site writewithharper.com) à la place de Grammarly. Demande-moi où j'écris le plus (Chrome, Firefox, Edge, VS Code, Obsidian, WordPress, application macOS) puis guide-moi pas à pas pour installer la bonne extension depuis les liens officiels de la page writewithharper.com/get, et pour la régler : variante d'anglais, règles à désactiver si elles sont trop tatillonnes. Fais-moi taper une phrase avec deux fautes pour vérifier que Harper les souligne. Rappelle-moi qu'il ne corrige que l'anglais, pas le français.

Review the GitHub repository and check whether it is safe to install given my machine and my infrastructure. Ask me as many questions as possible, using widgets, to clarify my request and be as precise as you can.
  2. 2

    Pick your English variant

    In the extension settings, pick American or British: Harper adapts the spelling (color, colour) and stops correcting you the wrong way.

  3. 3

    Add your words to the dictionary

    A product name or a trade term underlined? Add it to the dictionary once, it will not come back.

What you actually do with it

Your emails and messages in English

LinkedIn, Slack, customer support: mistakes are underlined before you hit send, without the text leaving for a third party.

Your notes and docs in Obsidian or VS Code

The plugin checks Markdown as you write, including offline on the train.

Your WordPress articles

The WordPress plugin proofreads your pages in the editor: fewer typos published, no subscription for the team.

Project health, at a glance

Before installing an open-source tool, one question matters: is the project alive? These scores are computed from public GitHub data. They are not made up.

89/100

Excellent

Very active, well-maintained project: go ahead with confidence.

Activity
100

Is the code moving? (commits in the last 30 days)

Maintenance
100

How fresh is the latest update? Fresher is better.

Community
88

Stars and contributors: people around means help and fixes.

Maturity
90

Project age. Old enough to be solid, still alive.

Momentum
66

Current pace versus its usual pace: speeding up or dozing off?

The repo in numbers

GitHub stars
17.3k
Forks
788
Contributors
160
Commits
4.9k
Project age
3 yrs
Last commit
today
Size
43.8 MB
License
Apache-2.0

Built with

  • Rust 52.9%
  • HTML 32.2%
  • TypeScript 7.3%
  • Svelte 5.4%
  • JavaScript 0.8%

Scores computed automatically from the GitHub API (last-30-days activity, update freshness, community size, project age). Refreshed daily.

Loucash’s take

8/10

If you write in English and pay for Grammarly, Harper gives you the same basic checking, free, instant, and your text never leaves your machine. That is the argument that matters when you write client emails or internal docs. What I like: the speed (nothing to wait for), the number of places it installs into, and Automattic behind it, the WordPress company: the project will not vanish, it ships a release every couple of weeks. What may bite: it only checks English, full stop. If you mostly write in French, it is not for you. It does not rewrite your sentences either, the way Grammarly Pro does, it corrects. And it can be picky: turn off the rules that annoy you, two clicks.

It’s for you if: You write in English every week (clients, content, code) and you want checking without a subscription or your texts leaking. If you only write in French, move along.

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