How do conditional edges work in LangGraph, and when do you use them?

What you need to know

1from typing import Literal, TypedDict2from langgraph.graph import StateGraph, START, END34class State(TypedDict):5    amount_inr: int6    fraud_score: float7    route: str89def route_refund(state: State) -> Literal["auto_refund", "human_review", "reject"]:10    if state["fraud_score"] > 0.8:11        return "reject"12    if state["amount_inr"] > 5000 or state["fraud_score"] > 0.4:13        return "human_review"14    return "auto_refund"1516builder.add_conditional_edges(17    "score",18    route_refund,19    {"auto_refund": "auto_refund", "human_review": "human_review", "reject": "reject"},20)

Parts of a conditional edge

• Source node — "score": the edge is checked after this node runs.
• Routing function — takes state (and optionally config or runtime), returns where to go.
• Path map — optional dict or list of targets. Without it, LangGraph cannot draw the possible branches, and the diagram shows edges to every node.

What the function may return

Prebuilt routing

tools_condition from langgraph.prebuilt returns "tools" if the last AI message has tool calls, otherwise END. It is the standard edge in a hand-built tool loop.

A real-life example

A marketplace's refund graph scores each request, then routes. In the first month, 72% of requests went to auto_refund, 25% to human_review and 3% to reject. When the fraud team wanted to lower the approval threshold from Rs 5,000 to Rs 3,000 during a festival sale, it was a one-line change in route_refund, covered by a unit test that passes three small state dicts and checks the three routes. No prompt was touched.

Follow-up questions to expect

• "Conditional edge or Command?" — Conditional edge when routing is a separate rule from the node's work; Command when the node itself already computed where to go.
• "Can the routing function be async?" — Yes, but keep it cheap. If it needs a model call, make that a node that writes a field.
• "What if it returns a name that is not in the path map?" — The run fails with an error. Use Literal return types and a default branch to avoid it.