Can you avoid sending data to the internet entirely by having Claude build a tool that runs locally?

Yes, you can ask Claude to build a tool that lives locally as a desktop program you click to open, so no data goes to the internet. However, this only works if the tool doesn't need live AI reasoning — for example, if you feed it a fixed rule set like GAAP standards to use as its 'only brain,' it can run offline. But if you want the tool to use ongoing AI reasoning to make judgment calls on transactions, it needs to connect back to the AI service, which is inherently less secure because data is going out to the AI.