Why do I need to convert HEIC to JPG?
HEIC is the default photo format on iPhone since iOS 11 — it compresses better than JPG at the same quality, but plenty of Windows software, older devices, and websites still can't open it directly. Converting to JPG turns it into a format that opens everywhere without a second thought.
Does this only work in Safari?
No. HEIC decoding is usually only built into Safari/macOS, which is why most browser-based tools quietly fail or ask you to convert first on other browsers. This tool decodes HEIC itself using libheif compiled to WebAssembly, so it works the same way in Chrome, Firefox, or Edge.
Will the converted JPG look different from the original HEIC?
Visually, no — HEIC and JPG are both lossy formats aiming for the same visual result, just with different compression. The JPG file will usually be somewhat larger than the source HEIC at an equivalent quality setting, since HEIC's codec (HEVC) compresses more efficiently than JPG's — that's a property of the format, not a sign anything went wrong.