Q.Cherry tomatoes
Tomatoes are growing fine but they are black at the stem and top of tomato. What could be the problem?
Without an image, I can't really determine if there is an issue or you have normally growing tomatoes.
The coloration could very well be related to the variety that you are growing.
Here are some links that have information on some of the most common diseases in tomatoes.
https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-diseases.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-bacterial-speck.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/early-blight-alternaria-tomato-leaf-spots-yellow-leaves.htm