Right - I have a ton of coworkers who obsess over "skills" and different ways to run agents and whatnot but I just... spend some time to give very thorough, detailed instructions and it just Does The Thing. I rarely fight with Claude Code these days.
We probably need something like the WET principle for skills. If you need to explain the same thing to an agent more than twice, turn it into a skill (or add it to AGENTS.md, or CLAUDE.md, or to you docs folder, or your guides folder, or whatever method you use). If you haven't needed to explain it more than twice, it's probably fine. The context pollution from the skill would likely be worse than not having the skill
Of course exceptions apply. Some basic information that will reliably be discovered is still worth adding to your AGENTS.md to cut down on token use. But after a couple obvious things you quickly get into the realm of premature optimization (unless you actually measure the effects)
Same here. For me, this means a spec doc split into features/UX, technical requirements, and language-specific requirements, iterated before the model touches code.