Why photos come out sideways
Phones store most photos the way the sensor captured them and add an orientation tag telling viewers how to turn them. Some websites, older programs and printers ignore that tag, so the picture appears on its side. This tool reads the tag first, shows the photo the way your phone does, then saves the pixels the right way up, so the result looks the same everywhere.
Rotate versus flip
Rotating turns the whole picture around its centre, like turning a printed photo on a table, and any text in it stays readable. Flipping mirrors it: a horizontal flip swaps left and right, which fixes the reversed text in some front-camera selfies and scans, and a vertical flip swaps top and bottom. A horizontal and a vertical flip together give the same result as a 180 degree turn.
Quality and file format
PNG images are saved losslessly, so every pixel is kept. JPG and WebP are re-encoded at high quality (92%), because a canvas cannot rotate the compressed data directly; the difference is very hard to see, but the file size may change a little. If your browser cannot write WebP, the image is saved as PNG instead and the file name shows it. Other formats such as GIF or BMP are also saved as PNG.
What happens to photo details
Redrawing the image on a canvas does not copy the camera model, date or GPS location stored inside the original file, so the downloaded copy carries none of them. That is often welcome when you share pictures, but if you need the original date, keep the original file as well. The orientation tag goes too, since the pixels themselves are now the right way up.
Free, private and its limits
There is no account, watermark or daily cap. Images are processed in your browser and never uploaded. You can add up to about 200 MB of images in one go; very large photos of more than about 50 megapixels may fail on some phones because of browser memory limits, in which case do them one at a time or on a computer. To change the size or framing as well: