Who is behind this
Vitamin D Explorer is built and maintained by Javier Aguilar. There is no company behind it and no content team: there is one person who decided the question "how much sun do I need today?" deserved a calculated answer rather than a rule of thumb.
Why it exists
The usual answer — "ten or fifteen minutes a day" — is the same in Oslo in December as in Nairobi in June, and in one of those places it is impossible. Vitamin D synthesis depends on solar elevation, ozone, phototype and the area of skin exposed. All of that can be computed, and that is what this tool does.
Contact and code
The model, its sources and its limits are published. If you find an error in a calculation, I want to hear about it.