Cropping is not resizing, and the difference matters
A crop selects part of the picture and throws the rest away. Every pixel that survives is bit-for-bit the pixel that was there before — no interpolation, no softening, no quality loss beyond whatever the output format costs you.
A resize changes how many pixels there are, which always means inventing or discarding detail. Plenty of "crop" tools quietly resize as well, usually to fit a preset, and the result is a slightly soft picture that nobody can quite explain.
This tool copies the rectangle at 1:1 by default. If you pick a platform preset and ask for the exact output size, it will scale afterwards — and it says so, rather than doing it silently.
Typed numbers beat dragging when it matters
Drag handles are right for composition — you can see what you are keeping. They are wrong for anything that has to be exact, because a handle is a few pixels of pointer precision against however many pixels of source.
So the four fields are authoritative: type Left, Top, Width and Height and that is the rectangle you get. The one you just typed always wins — if the rectangle no longer fits, the tool gives way in the other dimension rather than quietly changing the number you entered.
The two views stay in sync. Drag a handle and the numbers follow; type a number and the handles move.
Ratios, and where the thirds guide helps
A locked ratio is what you want for anything that will be displayed in a fixed frame — a 1:1 avatar, a 16:9 header, a 4:5 portrait post. Without the lock you will end up a few pixels out and the platform will crop again, usually badly.
The rule-of-thirds overlay is a composition aid, not a rule. Putting a horizon or a subject near a third-line tends to read better than dead centre, which is why it is worth having on screen — but a centred subject is a legitimate choice and plenty of good photographs are centred.
What the overlay is genuinely useful for is spotting a horizon that is not level, because the grid gives your eye a reference the picture does not.
Nothing is uploaded
The image is decoded, cropped and re-encoded entirely in your browser. This site makes no external requests at all — you can confirm that in your browser's network tab, which is a better assurance than any privacy policy.
That matters more for photographs than for most files. A picture can carry GPS coordinates, a camera serial number and a timestamp in its metadata, and it can carry faces regardless.
If you want to see what a photo of yours is carrying, the metadata tool reads it without uploading it either.