I've heard from a number of folks that they're seeing Claude Code just...not use skills they have installed.
The way Claude knows about skills is that it builds a big list of skill names and descriptions and injects it into in the system prompt.
The problems start when you've got too many skills or their description fields are too long. Then, the system prompt doesn't tell Claude about them. And if it doesn't know about them...it can't use them.
To add insult to injury, the system prompt tells Claude never to use skills that aren't listed.
As of Claude Code 2.0.70, the limit for skill and command descriptions defaults to 15,000 characters (or around 4000 tokens). If you're not making heavy use of skills, that ought to be fine. But, since there's no warning when you go over, you might find yourself with unusable skills.
For now, the best workaround is to set an environment variable:
SLASH_COMMAND_TOOL_CHAR_BUDGET=30000 claude will give you double the headroom for skill descriptions.
I've been working on making Superpowers a little bit more system-prompt token efficient. Superpowers 4.0, which should ship "soon", combines a number of infrequently used skills and rewrites a number of skill descriptions to be a bit shorter. But more on that soon.