Privacy-First Grammar Checkers for Mac
Every time you use Grammarly, your text is sent to their servers, processed, and stored. Their privacy policy allows using your content to improve their products. If you write anything sensitive — legal documents, medical notes, business strategies, personal journals — that's a problem.
Why Privacy Matters for Grammar Checkers
Grammar checkers see everything you write. Unlike a search engine that sees a query, or a social network that sees a post, a grammar checker processes your most private text — emails to your lawyer, messages to your doctor, business contracts, personal notes.
Here's what major grammar checkers do with your text:
- Grammarly — Text is sent to servers, processed, and stored. Privacy policy allows use for "product improvement." Requires an account with your email. See how to cancel Grammarly if privacy is a deal-breaker.
- ProWritingAid — Text is processed on their servers. Stored temporarily for processing.
- QuillBot — Text is processed on servers owned by Course Hero (now part of Learneo). Data practices unclear.
If you work with sensitive information — or simply value your privacy — you need a grammar checker that treats your text as ephemeral.
Three Levels of Privacy
| Level | How It Works | Privacy | Trade-off |
|---|---|---|---|
| On-device | AI runs locally on your Mac | Maximum | Less accurate, needs powerful hardware |
| Cloud, no storage | Text sent to AI, processed, immediately discarded | High | Requires internet, text in transit |
| Cloud, stored | Text sent, processed, stored on servers | Low | Best AI quality, but privacy risk |
Privacy-First Grammar Checkers Compared
1. FlowWrite — Cloud, No Storage (Best Balance)
FlowWrite sends your text to an AI model for correction and immediately discards it. Nothing is stored, logged, or used for training. There's no account — so there's no email, no profile, no personal data to collect.
- Text processed and immediately discarded
- No account or personal information required
- No analytics or usage tracking
- HTTPS encrypted, HMAC-SHA256 authenticated
- Works in every Mac app
- Free (20/day) or $2.99/month
Best for: Users who want strong AI accuracy with high privacy. Your text touches a server briefly but is never stored.
2. Apple Writing Tools — On-Device (Maximum Privacy)
Apple Writing Tools processes most requests on-device using Apple Intelligence. Your text never leaves your Mac for basic proofreading. Some features (like longer summaries) may use Apple's Private Cloud Compute.
- On-device processing for most features
- No data collection
- Free, built into macOS 15+
Best for: Users with maximum privacy requirements who only write in Apple apps and accept its limitations.
3. Harper — On-Device, Open Source
Harper is a fully offline, open-source grammar checker for developers. It runs entirely locally with zero network requests. Available as a VS Code/Neovim extension and CLI tool.
- 100% offline — no network requests ever
- Open source (Apache 2.0)
- Free
- Developer-focused (VS Code, Neovim, CLI)
Best for: Developers who want grammar checking in code editors with zero network activity.
4. LanguageTool — Self-Host Option
LanguageTool's core grammar engine is open source. You can download and run it on your own server, giving you full control over where your text goes. The hosted version processes text on their servers.
- Self-hosted option for maximum control
- 30+ languages
- Requires technical setup for self-hosting
- $5/month for hosted premium
Best for: Technical users who want to run their own grammar checker server.
Privacy Comparison Table
| Tool | Processing | Text Stored? | Account? | System-Wide? |
|---|---|---|---|---|
| FlowWrite | Cloud | Never | No | Every app |
| Apple Writing Tools | On-device | Never | No | Apple apps |
| Harper | On-device | Never | No | Code editors |
| LanguageTool (self) | Your server | You control | No | Some apps |
| Grammarly | Cloud | Yes | Yes | Partial |
Which One Should You Choose?
For most Mac users: FlowWrite offers the best balance — AI-powered accuracy with no data storage, no account, and system-wide coverage. Your text is processed and immediately forgotten.
For maximum privacy: Apple Writing Tools (if you only use Apple apps) or Harper (if you're a developer). Both process everything on-device with zero network activity.
For self-hosters: LanguageTool gives you full control by running the grammar engine on your own infrastructure.
The key question is: do you trust a grammar checker to see your text but not keep it? FlowWrite says yes — process it, correct it, forget it. Your text is ephemeral, as it should be.
Try FlowWrite free → — 10 corrections/day, no account needed.