Is it will do or we'll do?

It is my understanding that this expression should be used accordingly, as it relates to the number of people involved in performing the task at hand.

"Will Do." For example: If I am texting with my friend Jacob, and he asks me, "Will you run by the store and grab me an ice cold Cherry Limeade on the way out to my house?" I would respond by using the expression "will do." I would respond this way, because I am the only person performing an action in this situation. In this situation, "Will do" is equal to, and/or short for, "I will do that."

"We'll Do." For example: If my friend Luis sends me a text and says to me, "Hey, let's go downtown and eat at that new restaurant." I would respond to this request by texting the Words, "We'll do!" I would respond this way, because both of us are performing the action of eating at the restaurant. In this situation, "We'll do" is equal to, and/or short for, "We will do that."