How the Sun Protection Advisor works

The Sun Protection Advisor uses Open-Meteo for geocoding, weather forecast and UV forecast data. City search text is sent to Open-Meteo only to resolve a location, and selected coordinates are sent to Open-Meteo only to retrieve the forecast.

The tool separates forecast data from general protection guidance. Open-Meteo values are forecasts, not live sensor measurements. General sun-safety wording is based on sources already used by the project, including the World Health Organization and the American Academy of Dermatology.

The tool starts with the selected location's local time. If you choose “Now,” it calculates from the current local time for that location. If you choose a time, the app validates that the time is still usable for today in that location's IANA timezone.

Duration options use fixed planning windows: less than 30 minutes, around 1 hour, 2–4 hours and most of the day. The app compares that planned interval with the hourly UV forecast and uses the highest usable forecast UV value that overlaps your planned time outside.

The recommendation also considers activity type, water or heavy sweating, and makeup because those factors can change the practical protection steps. They do not numerically change the forecast UV value.

Makeup affects practical reapplication guidance. The app does not assume cosmetic SPF or a light makeup-friendly top-up is the same as a fully applied sunscreen layer, and the guidance becomes stronger for prolonged exposure, water, heavy sweating or stronger UV. Negligible planned UV exposure remains proportional and does not create a stronger makeup warning by itself.

Missing, null or invalid hourly UV values are ignored. If no usable hourly value covers the planned interval, the app shows a safe error instead of generating a result. The UV 3+ protection window is calculated from the first hourly forecast period at UV 3 or above through one hour after the final qualifying period, capped at local midnight.

Shared plans do not preserve an old timestamp. A shared “Now” plan is recalculated at the time the link is opened.

The Useful Kind provides educational, practical guidance. It does not diagnose conditions, calculate exactly when an individual will burn, or replace advice from a doctor, pharmacist or other appropriate healthcare professional.

The tool cannot know how much sunscreen was applied, whether coverage is even, all medications, skin conditions or individual sensitivities. Forecast data can change, and real exposure is affected by shade, clothing, reflective surfaces, behavior and local conditions.

Shared links preserve non-sensitive planning choices such as the selected place label, optional country code, activity, duration, timing mode, makeup and water/sweat answers. They do not store coordinates, old forecast values or recommendation text in the URL.

Opening a shared plan resolves the place again through Open-Meteo, retrieves fresh forecast data and generates a new result. Device-location-only plans may not produce a restorable link because precise coordinates are intentionally not serialized.

Privacy-limited product analytics use anonymous identifiers to understand whether people start plans, complete plans or use sharing. Custom analytics properties do not intentionally include precise coordinates, searched place text, recommendation content, names or email addresses.

The analytics provider may process standard technical web metadata such as browser, page and anonymous session information. Analytics are not used for medical profiling. The About page summarizes the broader privacy approach.