Documentation should be high-level

A few days ago, our team launched a new component. A week after launch, while dealing with some ops tickets, we discovered that the detailed, extensive wiki document for that component was already out-of-date.

This is a familiar story to any dev. Documentation is hard to keep accurate. The knee-jerk reaction is to assess that the miss here was that we allowed the documentation to become inaccurate. The knee-jerk reaction is wrong. It is not feasible to maintain documentation if that documentation is too specific.

The solution is to change the philosophical approach to documentation. For software systems of any reasonable complexity, the code is the only source of truth for its behavior and its descriptive reality. Documentation ought to answer the following questions, in basic non-technical english prose:

  1. Why did we create this component? (prescriptive statement)
  2. At a high-level, how does it solve its problem? (This answer should absolutely not map anywhere near 1:1 to its implementation. It should be at an extremely high-level.)
  3. Going no deeper than a file/class level view, describe in a paragraph the function of the most critical classes/files/modules in the code. This is as specific as it should get, and this serves as a guide for an engineer to dive into the code.

Again, documentation should never map 1:1 to anything more specific than a class. Anything more specific than that, and it effectively has to change whenever the code changes. If you’re changing the function of tons of classes and files, it is reasonable to expect that the documentation would necessarily have to change in kind.

Writing documentation at a high-level helps to minimize the potential that your documentation will become out-of-date and inaccurate. It is easier to understand, too. Which is kind of the point. If someone wants to know the objective truth exactly as it exists, the documentation is absolutely the wrong place for that. That’s what the code is for.