Show HN: Gemtype – an open source Grammarly alternative Chrome extension

Gemtype, an open-source Chrome extension, offers live grammar and spelling checking, sentence verification, and rewrite features using Google's Gemini API with a bring-your-own-key model, providing a free and private alternative to Grammarly.

Live grammar and spelling checking — underlines appear in any text field about a second after you stop typing: Gmail, LinkedIn, X, Reddit, GitHub, anywhere One-click fixes — click an underline and accept the correction; Ctrl/Cmd+Z always undoes Sentence verification — after every accepted fix, the surrounding sentence is automatically re-checked, so word-level fixes never leave broken sentences behind Rewrite on demand — select text for a floating toolbar with Improve, Fix, Shorten, Formal, and Casual actions, also available from the right-click menu Context-aware suggestions — an LLM judges whole sentences in any language, not just pattern rules Bring your own key — uses your free Google AI Studio https://aistudio.google.com/apikey key; no account, no subscription, no middleman server Private by design — text goes only to Google's Gemini API; no tracking, no analytics, nothing else phones home Full control — per-site disable, global toggle, model picker, language setting; honors data-gramm="false" opt-outs | GemType | Grammarly | | |---|---|---| | Price | Free — bring your own Gemini key | What does "bring your own key" really cost? For a single person typing, the free Gemini tier is more than enough — GemType checks only after you pause, skips unchanged text, and caches results, so even a heavy writing day stays comfortably inside the free quota. On the paid tier, a typical check costs around $0.0003 — roughly one dollar per month for very heavy daily use, compared with $144–360 per year for Premium. Live checking — underlines and issue-count badge | Click an underline, accept the fix | Review all suggestions from the badge | Select text to rewrite: Improve, Fix, Shorten, Formal, Casual | Install from the Chrome Web Store — one click, then add your free Gemini API key from Google AI Studio https://aistudio.google.com/apikey . Or install manually developer mode Manual developer mode : - Download or clone this repository - Open chrome://extensions and enable Developer mode - Click Load unpacked and select the extension/ folder - Get a free API key at aistudio.google.com/apikey https://aistudio.google.com/apikey no credit card required - Open GemType Settings from the toolbar icon, paste the key, and click Save & test Safari — the same code base wraps into a Safari App Extension; see Safari build safari below. page any website ┌──────────────────────────────────────────┐ │ content script │ │ ├─ detects textarea / contenteditable │ │ ├─ draws underline overlay shadow DOM, │ │ │ never touches the page's editor │ │ └─ applies fixes via execCommand │ │ native undo + framework-safe │ └──────────────┬───────────────────────────┘ │ chrome.runtime messaging ┌──────────────▼───────────────────────────┐ │ background service worker │ │ ├─ queue + cache + 429 backoff │ │ └─ Gemini generateContent │ │ structured JSON output │ └──────────────┬───────────────────────────┘ ▼ generativelanguage.googleapis.com your API key, your data Overlay, not injection — underline positions come from Range.getClientRects rich editors or a mirror element plain fields ; the page's DOM is never modified, so React, Vue, and ProseMirror editors stay stable Snippet anchoring — the model returns exact text snippets, located client-side and re-anchored live as you type LLM character offsets are unreliable Token-frugal — debounced checks, unchanged-text skipping, response caching, and sentence-scoped re-checks keep free-tier quota comfortable for daily use | Editor type | Status | |---|---| Plain textarea / input GitHub, forums, most forms | Supported | contenteditable rich editors Gmail, LinkedIn, X | Supported | | Shadow-DOM web components Reddit | Supported | | Google Docs canvas rendering; requires a Google-whitelisted extension ID | Not supported — use the right-click rewrite instead | - The text you are editing is sent only to generativelanguage.googleapis.com Google's Gemini API using your own key — see PRIVACY.md /riponcm/GemType/blob/main/PRIVACY.md - Your API key lives in chrome.storage.local on your device; it is never synced or transmitted anywhere else - Password fields are never read, and payment or one-time-code fields are skipped at the code level - No accounts, no telemetry, no third-party servers - Sites can opt out with data-gemtype="false" ; Grammarly-style opt-outs are honored as well extension/ the Chrome extension MV3, no build step ├── manifest.json └── src/ ├── background.js Gemini API calls, cache, rate limiting ├── content/ │ ├── content.js field discovery + checking loop │ ├── overlay.js underlines, badge, suggestion card │ ├── refine.js selection rewrite toolbar │ └── util.js text extraction, offset maps, safe replacement ├── options.html/js API key, model, language, disabled sites └── popup.html/js global + per-site toggles assets/ logo, hero animation, screenshots test/ ├── test-page.html manual test fields incl. scroll + opt-out cases └── harness.html automated harness with a mocked Gemini backend safari/ Xcode wrapper project generated run the mock harness no API key needed python3 -m http.server 8377 open http://localhost:8377/test/harness.html Safari build requires Xcode : xcrun safari-web-extension-converter extension --project-location safari --app-name GemType --macos-only xcodebuild -project safari/GemType/GemType.xcodeproj -scheme GemType -configuration Debug build Then in Safari: Settings → Developer → Allow unsigned extensions → enable GemType. - Chrome Web Store release — live now https://chromewebstore.google.com/detail/linnnamnhkciekgpnegkcajcafmjlhgh - Hosted key option proxy backend — zero setup for end users - Tone and style preferences per site - Safari App Store release build ready; needs Apple Developer membership — sponsor sponsor-this-project - Firefox port - iOS / Android keyboards sharing the same backend GemType sends the text you are actively editing to Google's Gemini API for analysis. Do not use it in fields containing passwords, secrets, or text you are not comfortable processing with a cloud AI service — or disable it for those sites with one click. Is GemType a free alternative to Grammarly? Yes. GemType provides live grammar checking, one-click fixes, and AI rewrites on any website at no cost — you supply your own free Gemini API key from Google AI Studio. There is no subscription and no premium tier. Is the Gemini API key really free? Do I need a credit card? Google AI Studio issues free API keys with no credit card required. The free quota is far more than one person needs for everyday typing; GemType is built to stay inside it debounced checks, caching, sentence-scoped re-checks . Is GemType safe? Where does my text go? The text you edit is sent directly from your browser to Google's Gemini API, authenticated with your own key. There is no GemType server, no account, and no analytics — the developers never see your text. Password, payment, and one-time-code fields are never read. See PRIVACY.md /riponcm/GemType/blob/main/PRIVACY.md . Which websites does it work on? Any site with a normal text field or rich editor: Gmail, LinkedIn, X Twitter , Reddit, GitHub, forums, web mail, CMS editors. Google Docs is the one notable exception, because it renders documents to a canvas and restricts its annotation API to Google-whitelisted vendors. Does it work in languages other than English? Yes. GemType auto-detects the language you are writing in and checks it with the same model — Spanish, French, German, Portuguese, Bengali, Hindi, Arabic, Chinese, Japanese, and anything else Gemini understands. You can also pin a language in settings. How is this different from pasting my text into ChatGPT or Gemini? GemType works where you type: mistakes are underlined in place while you write, fixes apply with one click and native undo, and each fix triggers an automatic re-check of the sentence. No copy-paste round trips. Does it slow down my browser? No. The content script stays inert until you focus a text field, checks only after you pause typing, and draws its UI on a lightweight overlay without touching the page's own editor. Can it run fully offline or with a local model? Not yet. A pluggable backend including self-hosted models is on the roadmap. Contributions are welcome — this project went from an empty folder to a working extension in a day, and there is plenty of interesting work left: - Firefox port WebExtension API is nearly identical - Compatibility fixes for stubborn editors report a site, ideally with a reduced test case in test/test-page.html - Translations for the UI - The proxy backend for a zero-setup hosted mode Open an issue to discuss anything bigger before you build it. If GemType helped you, starring the repository genuinely helps others find it. GemType is free, open source, and unfunded. The Safari version is built and working — but shipping it to the App Store requires the Apple Developer Program fee of $99/year , which is currently the only thing standing between this project and Safari users and, later, the iOS keyboard . If you or your company find GemType useful, consider sponsoring: github.com/sponsors/riponcm — the first goal is exactly one thing: the Apple Developer fee. Every sponsor is credited in this README. Apache License 2.0 /riponcm/GemType/blob/main/LICENSE © 2026 Ripon Chandra Malo Matily . See NOTICE /riponcm/GemType/blob/main/NOTICE . The GemType name and logo are trademarks and are not covered by the Apache license — see TRADEMARK.md /riponcm/GemType/blob/main/TRADEMARK.md . Please give forks their own name and icon. Another open source product from Matily — open source software studio.