A privacy-first writing assistant for your browser

Catches mistakes, explains them clearly, and helps you rewrite — entirely on your device. No account. No subscription. No telemetry. No paid AI.

WriteRight is a local, open-source alternative to Grammarly and QuillBot. Spelling, grammar, readability, tone and a transparent writing‑health score all run in the extension itself — there is no WriteRight server, and the default code path has nowhere to send your text. Optional AI rewriting uses your local model (Chrome's on‑device Gemini Nano, or an Ollama / LM Studio server you run) and nothing else.

• Private by architecture, not by promise — analysis never touches the network.
• Works fully offline — the language engine and a 152k‑word dictionary ship inside the extension.
• Free, forever — no tier, no upsell, no "premium" checks held back.
• Honest about limits — an editor it can't read cleanly is marked unsupported, not faked.

Click an underline (or press Ctrl/Cmd+.) for the category, a plain‑language explanation, and one‑click replacements. Every fix goes through a real input event, so the page's own undo still works — and it applies only while the original text still matches exactly.

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See it work

Rewrite a dense sentence

Over‑long or multi‑clause sentences get a blue Clarity underline. Rephrase tightens just that sentence — with your local AI when it's available, or a safe deterministic tidy‑up when it isn't.

Shift the tone

An uncertainty‑aware tone estimate across nine tones, plus one‑tap mode pills — shorter, formal, casual, friendlier, more confident, more persuasive, simplify — that rewrite only the text you select.

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Everything it checks

Local — always on, always offline	Optional local AI — off by default
Spelling & grammar (Harper, WebAssembly)	Rewrite shorter / longer · simplify
Punctuation, repeated words & spaces	Formalize · casualize · friendlier · confident · persuasive
Wordiness, weak phrasing, a buzzword list	Improve clarity · improve the conclusion
Readability — 5 grades + reading & speaking time	Rewrite for the current format preset
Writing Health Score — one published, transparent formula	Explain a sentence · free‑form chat
Tone — 9 tones, never a claim it can't back up	Sentence‑level Rephrase on any card
Clarity — hard‑to‑read sentence flags
Offline dictionary & thesaurus — 152k words, select‑to‑define (Alt+Shift+D)

The AI half runs on Chrome's built‑in on‑device model or an Ollama / LM Studio server you run — reached on 127.0.0.1 only, which CI enforces on every build. With AI off or unavailable, everything in the left column is unchanged.

Every check has its own switch (Options → Checks / Vocabulary, or the popup strip); turn one off and its underlines vanish live. Simple Mode enlarges every surface for new readers and language learners.

Full comparison against Grammarly and QuillBot: docs/FEATURE-PARITY.md.

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Private by architecture

• Spelling, grammar, readability, tone and score run entirely on your device — no network step, no server.
• No account, no telemetry, no crash reporting, no remote config, no remote code (the manifest ships only the wasm-unsafe-eval keyword the engine needs — WebAssembly, never eval).
• Password and credential fields are never read; hidden fields and code editors are skipped.
• Editor text lives in memory only. Your personal dictionary stays on this device.
• Local AI (optional) sends only the selected text, only to Chrome's on‑device model or a server on your own localhost. The whole page, other fields and hidden content are never sent.

Details: PRIVACY.md · Security model: SECURITY.md

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Install

Requirements: Node ≥ 22.13, npm. You never need a paid service to build or run it.

npm install          # also syncs the pinned Harper WASM
npm run dev           # Chrome, with live reload
npm run dev:firefox   # Firefox

For a loadable build:

npm run build:all     # → .output/chrome-mv3  and  .output/firefox-mv3

Load .output/chrome-mv3 via chrome://extensions → Load unpacked, or .output/firefox-mv3 via about:debugging → Load Temporary Add-on.

Supported browsers

Browser	Universal features	Notes
Chrome / Edge (stable)	✓	+ optional on‑device AI, native side panel
Firefox (stable desktop)	✓	+ local (Ollama / LM Studio) AI
Safari (macOS)	✓	packaged via safari-web-extension-converter; some contenteditable cases fall back to the sidebar

Brave, Vivaldi, Opera and Arc run the Chrome build. Full matrix and smoke checklist: docs/BROWSER_SUPPORT.md.

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Develop

npm run test          # vitest — unit + integration, against the real Harper WASM
npm run test:e2e      # Playwright — the packaged extension in a real Chromium
npm run check         # the full release gate (see below)

npm run check is the reproducible gate CI runs — typecheck, lint, format, a security‑audit suite (secret scan, dangerous‑API scan of the built code, no‑user‑text‑in‑logs, loopback‑only‑AI enforcement, SBOM, reproducible build), coverage thresholds, a golden‑corpus engine regression with false‑positive traps, and an engine precision/recall eval. No paid CI service required.

See CONTRIBUTING.md to add an editor adapter, a rule, or a browser‑specific enhancement · ARCHITECTURE.md for the engine pipeline · CHANGELOG.md for what's shipped.

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License

MIT — see LICENSE. Third‑party components and their licenses: THIRD_PARTY_NOTICES.md. Bundled: Harper (Apache‑2.0) and Open English WordNet (CC‑BY‑4.0).