Conditional edges: choosing a path

A conditional edge lets the graph look at the state and choose which node runs next: add_conditional_edges(source, router, targets) calls your router function and goes where it returns.

Last updated: 27 Sep, 2026 · LangGraph 1.2

So far every run goes the same way. But a billing complaint and a crash report should not get the same reply, and junk mail should get none at all. That is three outcomes from one starting point.

The add_conditional_edges call

def router(state):
    return "node_name"   # a node name to go there, or END to stop

builder.add_conditional_edges(source, router, ["node_a", "node_b", END])

The state

Start with the imports and the state. The state holds the incoming ticket and the reply a node will write back.

from typing_extensions import TypedDict
from langgraph.graph import StateGraph, START, END

class State(TypedDict):
    ticket: str   # the incoming message
    reply: str    # the answer a node writes

The handler nodes

Add two handler nodes, one per team. Each returns a fixed reply for now.

def billing(state):
    return {"reply": "We will refund the double charge."}

def technical(state):
    return {"reply": "Try logging out and back in."}

The router function

Here is the new idea. pick_team reads the ticket and returns where to go next: a node name, or END to stop. It is a plain function, not a node, so it is never added with add_node.

def pick_team(state):
    if "win a prize" in state["ticket"]:   # junk mail
        return END                         # stop, no reply
    # a charge goes to billing, anything else to technical
    return "billing" if "charge" in state["ticket"] else "technical"

Wiring the router

Wire the two nodes, then attach the router to START with add_conditional_edges. The list at the end names every place the router might send the run.

builder = StateGraph(State)
builder.add_node("billing", billing)
builder.add_node("technical", technical)
builder.add_conditional_edges(START, pick_team, ["billing", "technical", END])  # router picks the path
graph = builder.compile()

Running three tickets

Run three tickets through the same graph and print each reply.

for ticket in ["charged twice", "app will not open", "win a prize now"]:
    print(repr(graph.invoke({"ticket": ticket, "reply": ""})["reply"]))

Three tickets, three paths

The same pieces in one file, ready to run.

from typing_extensions import TypedDict
from langgraph.graph import StateGraph, START, END

class State(TypedDict):
    ticket: str
    reply: str

def billing(state):
    return {"reply": "We will refund the double charge."}

def technical(state):
    return {"reply": "Try logging out and back in."}

def pick_team(state):
    if "win a prize" in state["ticket"]:
        return END
    return "billing" if "charge" in state["ticket"] else "technical"

builder = StateGraph(State)
builder.add_node("billing", billing)
builder.add_node("technical", technical)
builder.add_conditional_edges(START, pick_team, ["billing", "technical", END])
graph = builder.compile()

for ticket in ["charged twice", "app will not open", "win a prize now"]:
    print(repr(graph.invoke({"ticket": ticket, "reply": ""})["reply"]))

Why each ticket went where it did

• pick_team is a function but not a node: it is never added with add_node, and it returns a destination, not a state update.
• Returning a string sends the run to the node with that name; returning END stops it.
• The third ticket gets an empty reply because pick_team sent it straight to END and neither reply node ran.

What the router may return

When to branch on the state

• Routing a request by its intent (billing vs technical vs spam).
• Skipping steps that do not apply, or ending a run early.

Related

• Previous: draw_mermaid: seeing your graph
• Next: Reducers: combining values in the state
• Reference: Graph API: conditional edges