What does Agile documentation look like?
Reading through Dusty Phillips' second edition of "Python 3 Object-oriented Programming," this quote caught my attention:
Further, the most important person you will ever have to communicate with is yourself. We all think we can remember the design decisions we've made, but there will always be the Why did I do that? moments hiding in our future. If we keep the scraps of papers we did our initial diagramming on when we started a design, we'll eventually find them a useful reference.
That strikes me as a good benchmark for acceptable documentation in Agile. Whether coder, UI/UX designer, data architect, or whatever, if you are keeping a good record of what you decided and why, you'll probably be able to recreate the rationale for why things got to be the way they are for anybody who needs to know. Especially if that anybody is you. And there is a good chance that someone following in your footsteps will be able to pick up the same rationale even in your absence. All this without putting an unnecessary burden on project progress for the sake of detailed documentation.
Of course, what qualifies as "good" is the tricky part. A suggested threshold would be to specify only as much information as makes sense or for what is known given the current situation. Documentation should be subject to iterative practices just as much as code.