I want to check quickly format of calc cells.
I think not all but if you have activated the formatting toolbar, you can see some of the options, and if you are using styles to format cells, you can see the style of the selected cell in formatting toolbar (activating apply style icon) and in the Styles & Formatting window [F11].
Thank you for the answer. I thought about checking if cell has [HH]:MM not HH:MM. If I could see format of all cells or if I could check format after marking the cell it would be great for me.
Then use styles, they are easy to create and apply and when you need change something, you only need to change in the style.
Since LO4.1 there is an experimentel Sidebar which has under Properties also the Number Format displayed. Unfortunately not real format only Time, Date and some other options. You might file an enhancement Bug here to include your feature.