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Measured on six things

Private on-device grammar checker and AI rewriter for Chr...

Security

HTTPS enforced with SPF and DMARC, but no HSTS, CSP, frame protection or Permissions-Policy — 6/12 on the header checklist. No SOC 2, ISO or bug-bounty page found. The on-device inference claim is the real security story and it's architecturally sound.

Screenshots

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Private Text Assistant

About this app

Private Text Assistant is a free Chrome extension that checks spelling and grammar and rewrites your text in 101 languages, all powered by the AI model built directly into Google Chrome on your own device. Unlike cloud-based writing tools, nothing you type on websites is uploaded anywhere, so your emails, drafts and documents stay completely private. You can select any text, pick a style such as Professional, Friendly or Shorter, and replace it in a single click. It detects the language of each sentence, meaning it handles mixed-language messages without a hitch, and it works wherever you write, from text boxes and email drafts to Google Docs and Google Slides. It requires Chrome 138 or newer on Windows, macOS, Linux or a Chromebook Plus, alongside 22 GB of free disk space and either a GPU with more than 4 GB of memory or 16 GB of RAM. For anyone who values privacy as much as polished writing, it is a genuinely refreshing alternative to mainstream grammar assistants.

Key features

1On-device grammar, spelling and style rewriting via Chrome's built-in AI model — no upload, no account.
2101-language support with per-sentence language detection for mixed-language messages.
3One-click style rewriting (Professional, Friendly, Shorter) that replaces selected text in place.
4Works in text boxes, email drafts, Google Docs and Google Slides.

Target customer profile

Drawn from the product itself, not from a survey.

Demographic

Privacy-conscious professionals

Pain points

Worried cloud grammar tools upload confidential text

Primary needs

On-device checking with zero data upload

Demographic

Multilingual remote workers

Pain points

Juggling several languages in one message

Primary needs

Accurate multi-language detection and rewriting

Demographic

Students and researchers

Pain points

Slow manual proofreading of long drafts

Primary needs

Fast one-click fixes across Docs and Slides

Scout Review

Written by AI from measured evidence, scored out of 100.

Private Text Assistant is a Chrome extension that does grammar, spelling and style rewriting entirely on-device using Chrome's built-in AI model, in 101 languages, with per-sentence language detection. The site is fast (95 mobile / 100 desktop Lighthouse), clean, and honest about requirements. The privacy claim is the whole product and it's architecturally credible. The weaknesses are the browser-layer security headers (6/12, no CSP or HSTS), a single contrast failure on accessibility, and a hardware floor that meaningfully narrows who can actually run it. For privacy-conscious multilingual users on capable machines, it's a legitimately interesting alternative to cloud grammar tools.

Measure by measure

Usability

One-click 'Add to Chrome', no account, no signup — the shortest possible path to value. Style presets are named concretely and the select-replace flow is explained in a sentence. Requirements are stated honestly up front, which is good practice but also a real friction point.

Design

Clean, confident single-column landing page with real product screenshots and a 30-language switcher. Feature blocks are short and legible; the mixed-language demo panel is the strongest visual asset. Judged on the marketing site — the extension UI itself is barely shown.

Speed

Lighthouse mobile 95/100 (LCP 2.6s, CLS 0, TBT 45ms) and desktop 100/100. The site is light, static-feeling and snappy. No user complaints about lag surfaced in the collected evidence.

Security

Accessibility

Lighthouse accessibility 96/100 with a single failing audit on color contrast. The site ships a 30-language UI switcher, which is genuinely broad locale coverage. No published WCAG statement, but the automated baseline is strong.

Growth

Real problem (confidential text + cloud grammar tools), specific wedge (on-device inference, 101 languages, mixed-language detection), but the 22 GB / 16 GB RAM / Chrome 138+ floor caps the audience hard. Domain is brand new — traction is context, not the score.

Improvement areas

Browser security headers are incomplete (6/12): no HSTS, CSP, frame protection or Permissions-Policy.
Hardware floor (22 GB disk, 16 GB RAM / 4 GB GPU, Chrome 138+) sharply limits the addressable audience.
No published security or accessibility documentation to back the privacy and a11y claims.
The extension UI itself is barely shown on the site — the demo panel is the only real look.

Design & Usability

The site is a competent, no-nonsense landing page: one CTA, four feature blocks, a real mixed-language demo, and a 30-language switcher in the header. Design is judged on the marketing site because the extension UI is barely shown — the demo panel is the only real look at the product. Usability is the stronger half: 'Add to Chrome', no account, no signup, style presets named concretely (Professional, Friendly, Shorter), and a select-then-replace flow explained in one sentence. The honest requirements block (Chrome 138+, 22 GB disk, 16 GB RAM or 4 GB GPU) is good practice but is also the single biggest friction point in the funnel — a lot of visitors will bounce at that line.

Speed & Security

Speed is the standout: Lighthouse mobile 95/100 with LCP 2.6s, CLS 0 and TBT 45ms, and desktop 100/100. The page is light and static-feeling, and no lag complaints surfaced. Security is more mixed. HTTPS is enforced and SPF/DMARC are configured, but the header probe found no HSTS, no CSP, no frame protection and no Permissions-Policy — 6/12 on the checklist. No SOC 2, ISO or bug-bounty page exists. The product's actual security argument is architectural: inference runs on Chrome's built-in model, so text never leaves the device. That's a strong claim and it's the reason to pick this over Grammarly — but the browser-layer hardening doesn't match the privacy branding.

Accessibility & Growth

Accessibility scores 96/100 on Lighthouse with one failing audit: insufficient background/foreground contrast. The site ships a 30-language UI switcher, which is broader locale coverage than most indie tools manage, though there's no published WCAG statement. Growth is a judgement on the idea. The problem is real — professionals genuinely worry about pasting confidential text into cloud grammar tools — and the wedge is specific: on-device inference, 101 languages, per-sentence language detection for mixed-language messages. Against LanguageTool, that's a genuine differentiator. The limit is the hardware floor: 22 GB free disk, 16 GB RAM or a 4 GB GPU, and Chrome 138+. That excludes most casual users and a lot of corporate fleets on managed Chrome versions. The idea can grow, but only as fast as Chrome's built-in AI ships to more machines.

Conclusion

If you write confidential material and you've been uneasy about pasting it into a cloud grammar checker, this is the most direct answer available right now — no account, no upload, one click. Check the requirements first: Chrome 138+, 22 GB free disk, and either 16 GB RAM or a 4 GB GPU. If your machine clears that bar, install it and run it against a real draft before you trust it with anything important. If it doesn't, bookmark it and come back when Chrome's on-device model reaches more hardware.

Suggestions for improvement

Add HSTS, a Content-Security-Policy and frame-ancestors to the response headers — 6/12 is thin for a privacy-branded product.
Fix the one failing contrast audit; it's a single CSS change between you and a clean accessibility score.
Publish a short security page explaining exactly how Chrome's on-device model is invoked and what, if anything, the extension can read.
Show the extension UI itself on the landing page — right now the demo panel is the only look at the actual product.

How we score

Alternatives comparison

Named competitors, point by point. Nobody paid to appear here or to be left out.

	Private Text Assistant	LanguageTool
Where the AI runs	On-device via Chrome's built-in model — no upload	Cloud API by default; self-hosted option for enterprises
Price	Free	Free tier; Premium subscription for advanced checks
Language coverage	101 languages with per-sentence detection	30+ languages for grammar; uneven depth per language
Style rewriting	Yes — Professional, Friendly, Shorter presets	Limited; focused on corrections, not tone rewriting
Hardware requirements	Chrome 138+, 22 GB disk, 16 GB RAM or 4 GB GPU	Any modern browser; no local compute needed
Account required	No	Optional; required for Premium