How many skills should my coding agent have?

Fewer, better ones. Ten hardened skills with clear triggers beat a hundred vague ones, because skills compete for the model's attention — overlapping triggers cause misfires and dilution. A practical stack: one process skill per workflow phase (debugging, review, planning), a few domain skills for your niche, and persona files for the rules that apply always. Add a skill when you catch yourself re-explaining the same procedure a third time; retire skills that haven't fired in a month. Treat the collection like code: versioned, tested, pruned.