Why is my cropped file bigger than the original photo?
Because the export is a PNG, which is lossless, while your source was almost certainly a JPEG, which is not. Even a small crop of a photograph can come out larger than the whole original JPEG. If you need a small file, crop here and then compress the PNG to JPEG or WebP with an image compressor.
How do I crop to exact pixel coordinates?
Use the X, Y, width, and height number fields rather than the drag handles. They are in the image's true pixel space, they are clamped so the box always stays inside the image, and they enforce a 16-pixel minimum on each side. If an aspect ratio is active, changing the width or height will recompute the other dimension to keep the ratio.
Does cropping lose quality?
No. The pixels inside the box are copied through a canvas at their original resolution with no scaling and no re-encoding, so what you keep is bit-identical to the source. The only losses are the pixels outside the box, which is the point, and the file's EXIF metadata, which is not carried into the export.
Is my photo uploaded anywhere?
No. The file is read into an in-memory image via an object URL, drawn onto an offscreen canvas, and exported straight back to a blob in your browser. There is no network request at any point, which is why it also works with the network off.
Why did my crop box jump when I picked an aspect ratio?
Selecting a ratio keeps your current width and recomputes the height from it. If the new height would extend past the bottom edge, the box is shrunk to fit and nudged back inside the image, which can look like it moved. Choose the ratio before you fine-tune the position rather than after.