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Lesson Content

What sub-agents are.

Sub-agents are separate Claude Code agent instances spawned by a parent agent (or the user). Each sub-agent has its own context window – its own focused conversation history and working state. A sub-agent completes a scoped task and returns results to the parent, which uses them to continue the larger workflow.

Why context management drives sub-agent use.

A Claude Code agent session's context window is finite. In a long, complex session:

• Early context gets compressed or dropped as the session grows
• The agent may have reduced recall of decisions and findings from early in the session
• Complex multi-domain tasks fill the context with information from multiple domains, diluting focus

Sub-agents address this by giving each domain or phase its own focused context:

• A sub-agent analyzing security has a context window dedicated to security findings
• A sub-agent analyzing performance has a context window dedicated to performance
• The parent aggregates findings with clean, high-level summaries – not raw detail

Tasks appropriate for sub-agents.

• Large codebase analysis: Each sub-agent analyzes a module or layer; parent aggregates
• Multi-phase projects: Each phase runs in a fresh sub-agent context; parent coordinates
• Parallel workstreams: Multiple sub-agents run independently on separate tasks; parent merges results
• Specialized analysis: Security sub-agent, performance sub-agent, documentation sub-agent – each with focused context

Tasks NOT appropriate for sub-agents.

• Simple, focused tasks that fit within a single context window
• Tasks where continuity of the full conversation history is important
• Tasks that require tight feedback loops between phases

Sub-agents add overhead: spawning, context transfer, result aggregation. Use them when the context management benefit outweighs the overhead.