Subagent Context Isolation - Claude Code

Context isolation is the defining feature of subagents. Work done inside a subagent stays there - only the summary comes back.

What it does

When you delegate to a subagent, its reads, tool output, and intermediate reasoning don't count against the main session's context. The main agent gets a condensed return value. This means a thousand-line exploration can resolve to a short answer without eating your window.

When to use it

• Any investigation that would otherwise clutter context.
• Large codebases where reading enough to answer a question costs a lot.
• Parallel fan-out with many independent branches.
• Keeping the main session focused on coding rather than scanning.

Gotchas

• Anything you need later has to make it into the subagent's return. If you lose it, you lose it.
• Subagent isolation isn't a security boundary - it's a context boundary.
• Over-delegating can fragment work. Some tasks want the main agent in-context.

Official docs: https://code.claude.com/docs/en/sub-agents.md