I haven't had much luck with skills being called appropriately. When I have a skill called "X doer", and then I write a prompt like "Open <file> and do X", it almost never loads up the skill. I have to rewrite the prompt as "Open <file> and do X using the X doer skill".

Which is basically exactly as much effort as what I was doing previously of having prewritten sub-prompts/agents in files and loading up the file each time I want to use it.

I don't think this is an issue with how I'm writing skills, because it includes skill like the Skill Creator from Anthropic.

Try adding a session hook that triggers on startup|resume|clear|compact to remind Claude about your custom skills.

Same experience here – it seems I have to specifically tell it to use the "X skill" to trigger it reliably. I guess with all the different rules set up for Claude to follow, it needs that particular word to draw its attention to the required skill.