Adding context: fork to a skill runs it in an isolated subagent instead of inline. The skill body becomes the subagent's task, the noisy work stays contained, and your main conversation gets back only the useful result.
Background subagents run concurrently, but they can't stop to ask you questions or negotiate permissions mid-run. Here is when concurrency saves time and when it just fails more quietly.
The description field is how Claude decides whether to delegate a task to a subagent. If it is vague, delegation misses or misfires. Here is how to write descriptions that work.
Skills are the right first abstraction in Claude Code. But once your tasks become large, noisy, or isolated, a plain skill stops being enough. Here is when subagents become the better tool — and how to combine both.