Are planks good for climbing?

Doing planks help strengthen your abs, back, and shoulders, among the other muscles it works.

These muscles are crucial for climbing, so if performing planks helps strengthen these muscles, then yes, doing planks should contribute to your climbing. The amount at which it contributes though is another matter, but generally speaking, doing planks and other exercises that improve core strength can help climbing.

Climbing relies very heavily on core, shoulder, and of course back strength. Training these muscles is important and can help climbers progress and climb better and harder.