The Critical Path

For the last ten years, if you had asked, I would have told you with some conviction that a “critical path” is a kind of test script that tests the essential functionality of a system. If the app passes it’s critical path test, I would have said, it may not delight users, but it’s unlikely that they’ll storm your basement with torches and pitchforks.

It came up at work during a discussion about interview questions. My colleague was both proud and surprised to have been the only person interviewed for his position that had known what it really means.

A critical path is a project management term that refers to the chain of dependant tasks that will take the longest amount of time in a project plan. For example, if I were to make a project plan for my breakfast on Sunday morning, it would look like this:

The plan for my sunday morning breakfast.

In this plan, making pancakes is the critical path. With an unlimited amount of people, and an unlimited amount of kitchen space, and all the resources and tools we would need, the fastest that we could produce my Sunday morning breakfast is the time it takes to make pancakes.

I can steam milk, flip pancakes, and toss a couple eggs in the pan all at the same time, but grinding coffee beans and mixing the pancake batter has to be done one at a time. This breakfast takes me just a few minutes longer than the critical path, so it’s not worth hiring a sous chef.

The time of a software projects is usually shaped more by the number of developers. We usually have a lot of features to deliver, and most of them are not directly dependant on each other. What you can see is a part at the beginning and end of a project where it’s hard to keep multiple people working, but that’s a whole other thing.

A generic project plan showing a chain of blocking tasks at the beginning and end of a project.

When a critical path is defining the time line for your project, it’s important to identify it; any step that gets delayed affects the entire chain. You should start these tasks as soon as possible, and do what you can to stop them from getting blocked.