iPhones save photos in HEIC format by default, which many apps, websites, and Windows programs still can't open properly. Converting HEIC to JPG (or PNG/WEBP) fixes that instantly. This tool decodes HEIC files directly in your browser, unlike so many free "convert HEIC" websites that quietly upload your photos to a server first.
HEIC is a newer, more efficient photo format Apple uses by default on iPhone, but support for it outside Apple's own apps is inconsistent, so many Windows programs and websites only accept JPG or PNG.
There's a small amount of quality loss inherent to converting between compressed formats, but at a high quality setting it's generally not noticeable.
Yes, this tool converts between JPG, PNG, WEBP, and HEIC (as input) in any direction, not just HEIC to JPG.