LangGraph/Core Model
Intermediate10 min

Nodes

Nodes as functions, async nodes, tool nodes, and the Command API for routing from inside a node.

Quick Reference

  • →Function nodes: any (state) -> partial_state function added via graph.add_node()
  • →Async nodes: use async def for I/O-bound work — LangGraph runs them with asyncio
  • →ToolNode: a pre-built node that executes tool calls from the model's response
  • →Command API: return Command(goto='node_name') to route from inside a node
  • →Nodes return partial state — only the keys that changed, merged via reducers

Function Nodes

STARTAgentLLM decides?conditionalneeds tooldoneENDToolsExecute & returnloop

START → Agent → Tools → Agent (loop) → END

The basic node signature
A node is any function that takes state and returns a partial state update. LangGraph merges the returned dict into the full state using reducers.
Partial updates only
Return only the keys you changed. The rest of the state is preserved automatically.