What Does Privacy-First Mean for a Grammar Checker?

Updated

Privacy-first means the grammar checker processes your text on your own device instead of sending it to a company's servers. Harper, an open-source grammar and spell checker, describes itself this way: "Every check happens locally. No cloud round-trips, no telemetry, no LLM in the loop." That combination—local processing, no telemetry, and no language model trained on your writing—is what separates a privacy-first checker from a conventional cloud tool. It suits writers and developers who handle confidential drafts, internal documentation, or client material and don't want that text leaving their machine.

What "privacy-first" actually covers

The term gets used loosely, so it helps to break it into concrete claims you can check:

  • Local processing. Grammar and spelling checks run on your device. Your text is not uploaded for analysis.
  • No telemetry. The tool doesn't report usage data, keystrokes, or error patterns back to the vendor.
  • No training on your text. Your writing isn't used to improve models. Harper states this directly: "certainty that we never train models on your writing."
  • No AI/LLM in the loop. Harper describes itself as "the only grammar checker that doesn't use AI," meaning suggestions come from rule-based logic rather than a generative model.

A tool can meet some of these and not others. A checker that runs locally but still phones home with usage statistics is not fully privacy-first. When evaluating any tool, match the vendor's claims against this list rather than accepting the label.

How local checking differs from cloud-based checkers

The core difference is where the text goes.

Dimension Privacy-first / local (e.g., Harper) Typical cloud-based checker
Where text is processed On your device On vendor servers
Data leaving your machine None, per vendor claim Full text or excerpts sent for analysis
Telemetry None, per vendor claim Often collected
Model training on your text Not used, per vendor claim Varies; check the policy
Speed Harper claims suggestions in under 10ms Depends on network round-trip
Works offline Yes Usually no
Language coverage Harper covers US, UK, Canadian, Australian & Indian English Often broad, varies by tool

The speed point follows from the architecture: with no network round-trip, a local checker can return suggestions almost instantly. Harper's page claims "suggestions in under 10ms." Cloud tools add latency that depends on your connection and the vendor's servers.

Practical trade-offs to weigh

Privacy-first isn't free of compromise. Consider these before switching:

  • Language coverage. Harper covers five English variants. If you write in other languages, check whether your tool supports them before committing.
  • Suggestion style. Rule-based checkers catch spelling, grammar, and style patterns reliably but won't rewrite whole sentences the way generative AI tools do. If you want heavy paraphrasing, a no-AI tool may feel limited.
  • Setup. Offline tools often run as editor extensions or local apps. Confirm the tool integrates with where you actually write—Harper's page emphasizes "every place you write," including markdown, which matters for developers.
  • Updates. Local tools still need updates to improve rules. Open source means you can inspect and contribute, but you're responsible for keeping it current.

How to verify a privacy claim

Don't take the label at face value. Use these checks:

  1. Look for open source. If the code is public, you or others can confirm there's no hidden upload path. Harper is open source, which makes its claims auditable.
  2. Test offline. Disconnect from the network and run a check. If it still works, processing is local. If it fails or degrades, text was likely going to a server.
  3. Check for an account requirement. A tool that demands sign-in to check grammar is probably tied to a cloud service. Harper's page presents local checking without an account as part of its pitch.
  4. Read the telemetry statement. Look for explicit "no telemetry" language rather than vague "we respect your privacy" phrasing.
  5. Confirm the training policy. Find a direct statement that your text isn't used for model training.

One clarification: privacy-first ≠ no useful suggestions

A common assumption is that avoiding AI means weak checking. That's not necessarily true. Rule-based grammar and spell checkers have decades of engineering behind them and handle spelling, punctuation, agreement, and common style issues well. Harper positions itself for "students, journalists, and devs"—audiences that need accurate, fast correction more than creative rewriting. The trade-off is in scope, not in basic usefulness: you get dependable mechanical checks without your draft leaving the device.

If your priority is keeping sensitive text local and you write in English, a privacy-first checker like Harper is a reasonable fit. If you need multilingual support or AI-style rewriting, weigh those needs against the privacy benefit before deciding.