Arca does not collect, store, or transmit any data to the developer or to any third party. The developer operates no server and has no access to any user's data.

When the optional auto-save feature is enabled, Arca reads image URLs and the post permalink from posts you explicitly like, bookmark, or save on x.com and pinterest.com. It downloads those images and uploads them, with their source URL, to a backend server whose address you configure yourself — by default a service running on your own computer at localhost. Nothing is sent anywhere else. Auto-save is disabled by default and is enabled per-site in the extension's popup.

Arca stores locally, in your browser: your backend URL, an optional API key, a cached list of your board names, a record of which images have already been saved, and a queue of pending uploads. The API key and backend URL use browser.storage.sync so they follow your Firefox account across your own devices; everything else is device-local. Arca contains no analytics, no telemetry, no advertising, no third-party SDKs, and no remotely-loaded code.