Transparency should not turn black
This is the most common complaint about format converters, and it is not a bug so much as a shrug: JPG has no alpha channel, so something has to go behind the transparent pixels. Many tools leave the canvas at its default — which is black — and hand you a logo on a black square. Pick the fill colour here before you convert. It defaults to white.
If the file gets bigger, that is expected
Converting a JPG or WebP into PNG almost always produces a larger file. The original threw away detail to get small; PNG is lossless and cannot throw anything away, so it faithfully stores every JPEG artefact. The results table shows the before and after size for each file so you find out here rather than at the upload box. Convert to PNG when you need transparency or exact pixels, not when you want a smaller file.
Animation gets flattened, and you will be told first
An animated GIF or animated WebP holds many frames. JPG and PNG hold one. Most converters silently keep frame one and say nothing. This page counts the frames when you drop the file and warns you before you convert anything.
What this browser can actually write
The output buttons above are not a fixed list — the page tests your browser when it loads and
only offers formats it genuinely produces. This matters more than it sounds. Asked for AVIF, Chrome
quietly returns a PNG instead, with no error. A converter that trusts its own dropdown will
hand you a file called photo.avif that is really a PNG, and it will fail to open
wherever you send it.
Your camera data is left behind
Photos carry EXIF metadata — camera model, timestamp, and often GPS coordinates. Because the picture is redrawn onto a canvas before it is saved, none of that survives into the converted file. The rotation flag is read and applied first, so the image still comes out the right way up. And nothing is uploaded to find that out: the conversion is done by about 12 KB of JavaScript in your own browser. Here is how that is enforced.
All HermitFile tools
Every one of them runs in your browser. Nothing you open is uploaded.