This is a free hobby site run by one runner. There is nothing to sell you and nothing to sell about you. Here is the complete picture, no legal fog.
Anonymous visit counts. We use Ahrefs Web Analytics, a cookieless, privacy-focused counter. It tells us things like which pages get visited, roughly what country visits come from, and what kind of device was used (phone or desktop). That is how we know whether anyone finds the site useful.
No cookies. No accounts. No email capture. No advertising or ad networks. No fingerprinting profiles. No selling or sharing of data, because there is no personal data to sell. We cannot identify you and do not want to.
Plans you build in the calculator are saved in your own browser's local storage so they are still there when you come back. They are never sent to a server. Clearing your browser data erases them. Shared plan links contain only the numbers you can see in the link itself.
That is the entire list. The site's code is open source, so you can verify every word of this page yourself.
Open an issue on GitHub and ask. Being able to answer this page honestly matters more to us than any statistic we could collect.