Skill vs Subagent
Adding knowledge to the current agent, versus dispatching a whole separate one
Skill
Changes what the current agent knows, in the current session, in the current context window. No new process, no separate context, the same agent simply gains instructions it did not have loaded a moment ago.
Subagent
A separate agent run with its own context window, dispatched to handle a piece of work independently and report back a result. It isolates noisy, exploratory work away from the main conversation entirely.
Which one do you actually need
Reach for a Skill when the current agent just needs to know how to do something it's about to do itself. Reach for a subagent when a task would flood the main context with noise, many files read, many attempts tried, and only the final answer actually matters to the conversation. A Skill keeps everything in one window, a subagent deliberately keeps most of the work out of it.