Korr has no analysis server. The correction engines ship with the website, the extension or the app, and run on your device. This page explains where, for each of the three, and how to check it without taking our word for it.
A service worker stores the page and the engines in the browser cache. Later visits are served from that cache, including with no connection. Spanish, Italian and Portuguese are downloaded the first time you check a text in that language, then kept the same way.
Each language runs in a Web Worker, a separate thread inside the browser. The text is corrected in memory and the result comes back to the page. No request leaves with your text.
The website installs as an app on Android, iPhone or desktop, from the browser menu. Same code, same cache: it works offline too.
All five engines are included in the extension file that Chrome installs (about 1.3 MB). Nothing is downloaded to correct.
Under Manifest V3, an extension's background script cannot start Web Workers. Korr therefore opens an offscreen document that hosts the engines locally and makes no network request.
To place the ✓ button in your text fields, the extension loads a script in the pages you visit. It reads the field's text only when you ask for a correction, and the button stays hidden until you enable it on a site.
The local engine is a small service that listens only on 127.0.0.1,
your own machine's address: it cannot be reached from the Internet. It runs on a Node.js
runtime bundled with the app, with nothing else to install. The Windows app checks French and
English.
The optional rewriting styles (professional, friendly, concise, translation) use a language model you install yourself on your machine, with Ollama. They stay local too, and correction works without them.
The language and style you picked, the sites where the button is enabled, and your personal dictionary. These settings stay in the browser's or extension's local storage, are never synchronised, and disappear when you uninstall.
The text you correct. It is not written to disk, kept in a database or transmitted.
The initial download of the website, extension or app, and, on the website, anonymous cookie-free audience measurement (Vercel Web Analytics). Neither contains your text.
To go further, open the browser developer tools (F12), Network tab, then run a correction: no request leaves with your text.
A grammar checker sees the most private things you write: emails, contracts, medical notes. Correcting locally removes the problem instead of promising to handle it. It is also what makes no account and no limit possible: there is no server to pay for or to protect. See what Korr checks, language by language.