Some browser tools can keep processing after the page loads, but that does not mean every tool is fully offline or that all input stays private. The page, scripts, fonts, and data may need a network request on reload; live rates, news, and server-side processing certainly need connectivity.
To test a specific tool, load it, disconnect, use a harmless sample, then reload while still offline. Inspect any clear error and cached-page behavior. For privacy, review the tool's data path separately; offline success alone does not prove that it never sends data while connected. MDN explains how caching can support offline pages.
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