Is it ok just to add your coffee grounds straight on the garden or do they need composting first?

When I've used them I've put them straight in the garden. Both mixed in the soil and on top as mulch.

Straight into the garden is fine.
I often pick them up from our local cafe and sprinkle them over the lawn.
You can over do it so don't use cafe quantities regularly but every so often is fine.

I rinse out my coffee plunger with the grounds straight into the kitchen bucket of compostables, so that all my compost has coffee grounds mixed fairly evenly through it. It's the easiest way of disposing of the grounds, with no waste. When I've tried mulching with coffee grounds from a local cafe, the grounds have gone mouldy.

I do the same, Karena.