Sub-Agent
A specialist agent invoked by an orchestrator with a narrow tool set and focused prompt.
Last updated: April 26, 2026
Definition
A sub-agent is a domain-focused worker. Examples: a "calendar" sub-agent that only has Google Calendar tools, a "research" sub-agent that only has web search and reading tools. Sub-agents have shorter prompts (specialization = fewer instructions), smaller tool catalogs (faster decisions), and clearer eval criteria. The orchestrator treats each sub-agent like a function: pass in inputs, get back outputs. The internal reasoning of a sub-agent does not leak to the orchestrator unless explicitly returned.
When To Use
Spin up a sub-agent when one agent's prompt has more than ~500 lines of instructions or when one capability has a fundamentally different tool set.
Building with Sub-Agent?
I've shipped this pattern in real production systems. If you want a second pair of eyes on your architecture, that's what I do.