Local processing
Local tools use browser capabilities such as Web Crypto, Canvas, FileReader and text parsers. After the page loads, the transformation happens on the device. This reduces exposure and often allows the tool to keep working offline.
Local processing does not remove every risk: browser extensions, a compromised device or malicious page code can still access data. Use trusted software and keep the browser updated.
When an external API is necessary
Current exchange rates, DNS records, geocoding and public IP data require information that is not stored in the browser. In these cases, the query is sent to an identified provider. Avoid including unrelated personal data in the request.
A quick privacy check
Look for a clear local or external API label. Check whether the tool works after disconnecting the network. Avoid services that demand an account for a simple conversion, and remove secrets from example payloads before sharing results.