Harper vs LanguageTool
Self-host pick — both replace Grammarly (Writing assistant / grammar + style checker).
Both Harper and LanguageTool self-host as a replacement for Grammarly (Writing assistant / grammar + style checker). Pick Harper if you want a Apache-licensed codebase (Apache-2.0); pick LanguageTool for GPL (LGPL-2.1). Both run in roughly the same cost bracket — $0 — harper runs locally (lsp) or in-browser (wasm) by default; no server required for personal use vs $5-10 vps; the larger n-gram dataset wants ~16gb disk + a few gb ram if you enable it.
| Harperopen-source | LanguageToolopen-source | |
|---|---|---|
| License | Apache-2.0 | LGPL-2.1 |
| Setup time | 5min — Rust binary, also runs as a VSCode extension and a browser extension | 10min — single Java process, optional docker-compose |
| Monthly cost | $0 — Harper runs locally (LSP) or in-browser (WASM) by default; no server required for personal use. | $5-10 VPS; the larger n-gram dataset wants ~16GB disk + a few GB RAM if you enable it. |
| GitHub | Automattic/harper | languagetool-org/languagetool |
| Replaces | Grammarly | Grammarly |
Good fit for
Harper
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.
LanguageTool
Anyone whose Grammarly use is mostly grammar + style + multilingual checking — LanguageTool covers 30+ languages.
Weak at:Tone, rewrite, and the AI 'make it sound more confident' features are not in the free OSS server.
In a terminal? npx -y github:SolvoHQ/os-alt-cli grammarly prints Grammarly's self-host options including both —
how the CLI works →
FAQ
Which is easier to self-host, Harper or LanguageTool?
Harper: 5min — Rust binary, also runs as a VSCode extension and a browser extension. LanguageTool: 10min — single Java process, optional docker-compose.
What does each cost to run?
Harper: $0 — Harper runs locally (LSP) or in-browser (WASM) by default; no server required for personal use.. LanguageTool: $5-10 VPS; the larger n-gram dataset wants ~16GB disk + a few GB RAM if you enable it.. Both projects are free and open source.
Do Harper and LanguageTool replace the same SaaS?
Yes — both are open-source alternatives to Grammarly.