Drop HEIC photos above, download standard JPGs. Batches are fine. Every file converts on your own device.
Why the file won't open: iPhones have shot HEIC by default since iOS 11. It stores photos in roughly half the space of JPG. Good for the phone, useless when a website, form or older Windows PC refuses the format. JPG opens on everything.
Quality and size: conversion runs at 90% quality. Visually identical in normal use. Expect the JPG to be larger than the HEIC, often by 20–40%, because JPEG's compression is decades older than the codec inside a HEIC and the same picture needs more room once it is written the old way. Originals are never modified.
Burst photos: a HEIC container can hold several frames, and the primary image is the one converted.
Stopping the problem at source: Settings, then Camera, then Formats, then Most Compatible makes the iPhone shoot JPG directly. Many people keep HEIC for the space saving and convert only when a form complains. iPhones already convert automatically when emailing and in most share flows. This page covers what slips through: USB transfers, cloud downloads, other people's files.
Each file shows its own progress and sizes, and downloads individually or as a ZIP. Sceptical about the no-upload claim? Watch the network tab while converting, or use the page with wifi off.