Why these exist
Most people arrive at a file tool mid-problem: a form has just rejected something, and they want it fixed. The tools handle that. These guides are for the questions that follow — why the limit is what it is, which format to pick, and how to avoid the same problem next time.
Each one is written to be read on its own rather than as marketing for the tools, though where a tool genuinely solves the problem being discussed, it is linked.
More to come
Topics get added when a question comes up often enough to be worth answering properly. If there is something you looked for and could not find, say so — that is generally how these get chosen.