Lossless. The GPS coordinates, camera serial number, owner name and timestamps come out. The pixels are never recompressed, and your ICC colour profile and photo rotation are kept exactly as they were.
Every file is read in your browser and rewritten byte by byte. Your photos are never uploaded. The page itself loads one ZIP library from a public CDN, records an anonymous page view, and when you press the button it sends an anonymous count of how many photos were cleaned. No filename and no part of any photo is ever sent.
You get back a ZIP holding every cleaned photo, plus metadata-report.csv if you left that box ticked. Each cleaned file is read back after it is written and is rejected if anything private survived, or if anything was left sitting after the end of the image, so a file only reaches the ZIP once it has come out clean on a second read. The report is not safe to pass on: it lists the coordinates and serial numbers themselves, so delete it before you send the photos anywhere, or untick the box above.
A photo taken on a phone usually carries the exact latitude and longitude of the spot it was taken, to about a metre. Post a picture of a finished landscaping job, a real estate interior, a contractor site visit or a product shot taken at home, and the file quietly carries the address with it. Camera bodies also stamp a serial number, and editing software stamps your name, your software licence and the date and time you worked. None of that is visible in the picture, so nobody thinks to check it.
Most online EXIF removers redraw your photo onto a canvas and save it again. That does remove the metadata, but it also re-encodes the image, which softens detail, adds JPEG artefacts, throws away the colour profile and usually loses the rotation tag so portrait photos come out on their side. This page does not touch a single pixel. It walks the JPEG marker stream, drops the metadata segments and copies the compressed image data through untouched, so the photo you get back is bit for bit the same picture with the private parts cut out. For PNG it removes the text, XMP, EXIF and timestamp chunks the same way.
It removes GPS coordinates and altitude, camera make, model and serial number, lens details, owner and artist names, copyright strings, capture timestamps, editing software names, maker notes, IPTC and Photoshop blocks, XMP packets, embedded comments and content credential blocks. It does not change anything you can see in the picture, so a street sign, a house number, a reflection or a screen full of text stays exactly where it is. It is also not tamper protection or a way to defeat image forensics. It removes the labels on the file, nothing more. JPEG and PNG are supported. HEIC, WebP, TIFF and RAW are refused with a reason rather than handed back looking clean when they are not.