How these tools actually work
Short version: everything runs inside your browser. The server is not involved.
These tools use capabilities the browser already has — JavaScript for arithmetic, Canvas for QR codes and image processing, the built-in Intl interfaces for currency and date formatting. None of them send your input to a server and wait for a response. That has two consequences: speed depends on your device rather than your connection, and whatever you type never leaves the machine you typed it on.
In several of these cases that matters more than the feature list itself. You do not want a generated password passing through somebody else's server. You do not want the text of a contract or a draft thesis stored as a row in a database you have never seen. You do not want work images uploaded to an object store in an unknown region. Local processing is not a marketing angle here; it is the only sensible design for this category of tool.
Why it is free
Because the cost structure allows it. These are static pages — no backend process, no database, no per-call API bill — so hosting costs approach zero and there is no honest reason to charge. The advertising on the page covers the domain and the bandwidth. There is no membership tier, no export restriction and no three-free-uses-per-day limit.
Does it work on a phone
Yes. Every tool page uses a responsive layout with touch-sized controls, and none of them require horizontal scrolling in portrait. Tools like the calculator, unit converter and QR code generator are arguably more convenient on a phone than on a desktop.
Do I need to install anything
No. There is no installer, no browser extension, no account, and no permission prompt. Open the page and use it; close the page and nothing remains.