Subagents are help you summon. A skill is the opposite: something Claude reaches for without being asked.
A skill is a file of instructions that Claude reads on its own — but only when the task in front of it matches what the skill is for.
You’ve already met two ways to give Claude standing knowledge back in Level 9: a CLAUDE.md file that’s always loaded, and slash commands you type. A skill is a third — and it’s the sneaky-powerful one.
Picture a cookbook on the shelf. You don’t reread the whole thing every time you walk into the kitchen. But the moment you decide to bake bread, you pull down the bread book. A skill is that: knowledge that sits quietly until the task calls for it, then gets opened.
How Claude knows to reach for it
Every skill carries a short description — essentially “use this when…”. Claude reads those descriptions, and when what you’re doing matches one, it opens that skill and follows the instructions inside.
You don’t type anything special. You describe your task the way you normally would, and the matching skill loads itself.
Here’s the aha: a skill isn’t a function you call or a command you invoke. It’s knowledge Claude pulls in on its own, when it’s relevant.
Why this beats pasting
Without skills, the only way to give Claude your team’s specific way of doing something is to paste it into the chat — every time, and only if you remember to.
A skill means you write it once. From then on, whenever that situation comes up, Claude already has it — even if you’ve forgotten the skill exists.
And because it only loads when relevant, it doesn’t clog every conversation the way a giant always-on CLAUDE.md would. The knowledge shows up exactly when it’s useful and stays out of the way the rest of the time.
What’s next
You now know three ways to give Claude standing knowledge — skills, slash commands, CLAUDE.md. They look alike and trip people up. Next, we line them up side by side.