What this online image converter is for
The single-format pages on this site exist because people search for the exact pair they need. This one exists for the other case: a folder with a bit of everything in it, and one target format you want them all in.
Drop the whole mix in, pick the output once, and every file follows the same
setting. Detection is per file and does not trust the extension blindly, which
matters because Windows reports PNG as image/x-png and some Android builds
report AVIF with no MIME type at all.
Choosing the output format
Three options, and the right one follows from what the image is rather than from preference.
PNG when the picture has hard edges, text, flat colour areas or transparency. Screenshots, logos, UI captures, diagrams and icons all belong here. PNG is lossless, so it is also the correct choice for anything you will edit again.
JPG for photographs that will not be edited further, and for any system that accepts nothing else. It has no transparency at all, so a cut-out subject gets flattened onto the background colour you choose.
WebP for anything going onto a web page. It keeps transparency like PNG and compresses like JPEG, which is the combination neither of the older formats offers, and every browser in current use reads it.
Why the read list is longer than the write list
This is the one thing worth understanding about any browser-based converter. Decoding and encoding are separate capabilities, and browsers ship far more decoders than encoders. Your browser can display AVIF, GIF, BMP and SVG, but its canvas can only write PNG, JPEG and WebP.
That asymmetry is why you will not find "convert to AVIF" here. A canvas asked
for an unsupported type does not fail; it quietly returns PNG data instead. A
file named .avif full of PNG bytes is worse than an honest refusal, so this
tool checks what the encoder actually produced and reports a mismatch rather than
handing you a broken file.
Everything is local
Files are decoded, redrawn and re-encoded inside this browser tab. There is no upload step, no queue and no server-side size limit, and no copy of your images exists anywhere afterwards.