Harper vs Grammarly

Self-host swap-in for Grammarly. · Self-host Grammarly · Harper on os-alt

Harper is one of the open-source self-host replacements for Grammarly — license Apache-2.0, 5min — Rust binary, also runs as a VSCode extension and a browser extension to stand up, and $0 — harper runs locally (lsp) or in-browser (wasm) by default; no server required for personal use. Compare against Grammarly's Free for basics; $12-15/user/mo for Premium; Business adds team analytics below.

	Harperopen-source	Grammarlypaid SaaS
Category	Writing assistant / grammar + style checker	Writing assistant / grammar + style checker
License / pricing	`Apache-2.0`	Free for basics; $12-15/user/mo for Premium; Business adds team analytics
Starting price	$0 self-host	$12/user/mo
GitHub	Automattic/harper ★ 10.5k · last commit todayalive	closed source
Setup time	5min — Rust binary, also runs as a VSCode extension and a browser extension	SaaS — sign up + bill
Monthly cost	$0 — Harper runs locally (LSP) or in-browser (WASM) by default; no server required for personal use.	from $12/user/mo (Free for basics; $12-15/user/mo for Premium; Business adds team analytics)

Switching from Grammarly to Harper

Install the Harper VSCode / Obsidian / Zed plugin or the browser extension. There is no migration data in Grammarly to bring over — switch the extension and point your IDE at the Harper LSP. For self-hosted as a server, run `harper-ls --stdio` behind any LSP-aware proxy or run the WASM bundle in your own page.

Good fit for: Devs who want grammar/style checking that runs fully on-device with low latency and zero data leaving the box.
Weak at: Younger project — fewer rules than LanguageTool; English-only at the moment.

Other open-source self-host alternatives to Grammarly

LanguageTool
LGPL-2.110min — single Java process, optional docker-compose$5-10 VPS; the larger n-gram dataset wants ~16GB disk + a few GB RAM if you enable it.
Vale
MIT10min — single Go binary + a styles directory$0 — local binary; CI cost only if you run it in pipelines.

In a terminal? npx os-alt grammarly prints Grammarly's self-host options — how the CLI works →

FAQ

Is Harper a free alternative to Grammarly?

Yes — Harper is open source under Apache-2.0. Self-host cost: $0 — Harper runs locally (LSP) or in-browser (WASM) by default; no server required for personal use.. Grammarly starts at $12/user/mo (Free for basics; $12-15/user/mo for Premium; Business adds team analytics).

How long does Harper take to set up vs Grammarly?

Self-hosting Harper: 5min — Rust binary, also runs as a VSCode extension and a browser extension. Grammarly is a hosted SaaS — sign up and you're in.

What is Harper good at, and what is it weak at?

Good fit for: Devs who want grammar/style checking that runs fully on-device with low latency and zero data leaving the box.. Weak at: Younger project — fewer rules than LanguageTool; English-only at the moment..