A good design doc can save you years of development time. Writing a design doc forces you to think through important decisions before you waste time on the wrong implementation. It’s also the best way to coordinate design decisions among teammates and partner teams.

I’ve written design docs as a developer at Google, Microsoft, and within my own companies. The specifics vary, but the underlying principles remain the same. A design doc articulates the hard problems you’re solving and helps your teammates give you feedback.

Below, I share my approach to creating effective design docs and explain what belongs in a design doc and what does not.