Use subgraphs

This guide explains the mechanics of using subgraphs. A common application of subgraphs is to build multi-agent systems. When adding subgraphs, you need to define how the parent graph and the subgraph communicate:

Shared state schemas — parent and subgraph have shared state keys in their state schemas
Different state schemas — no shared state keys in parent and subgraph schemas

Setup

npm install @langchain/langgraph

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Shared state schemas

A common case is for the parent graph and subgraph to communicate over a shared state key (channel) in the schema. For example, in multi-agent systems, the agents often communicate over a shared messages key. If your subgraph shares state keys with the parent graph, you can follow these steps to add it to your graph:

Define the subgraph workflow (subgraphBuilder in the example below) and compile it
Pass compiled subgraph to the .addNode method when defining the parent graph workflow

import { StateGraph, START } from "@langchain/langgraph";
import { z } from "zod";

const State = z.object({
  foo: z.string(),
});

// Subgraph
const subgraphBuilder = new StateGraph(State)
  .addNode("subgraphNode1", (state) => {
    return { foo: "hi! " + state.foo };
  })
  .addEdge(START, "subgraphNode1");

const subgraph = subgraphBuilder.compile();

// Parent graph
const builder = new StateGraph(State)
  .addNode("node1", subgraph)
  .addEdge(START, "node1");

const graph = builder.compile();

Full example: shared state schemas

import { StateGraph, START } from "@langchain/langgraph";
import { z } from "zod";

// Define subgraph
const SubgraphState = z.object({
  foo: z.string(),  // (1)! 
  bar: z.string(),  // (2)!
});

const subgraphBuilder = new StateGraph(SubgraphState)
  .addNode("subgraphNode1", (state) => {
    return { bar: "bar" };
  })
  .addNode("subgraphNode2", (state) => {
    // note that this node is using a state key ('bar') that is only available in the subgraph
    // and is sending update on the shared state key ('foo')
    return { foo: state.foo + state.bar };
  })
  .addEdge(START, "subgraphNode1")
  .addEdge("subgraphNode1", "subgraphNode2");

const subgraph = subgraphBuilder.compile();

// Define parent graph
const ParentState = z.object({
  foo: z.string(),
});

const builder = new StateGraph(ParentState)
  .addNode("node1", (state) => {
    return { foo: "hi! " + state.foo };
  })
  .addNode("node2", subgraph)
  .addEdge(START, "node1")
  .addEdge("node1", "node2");

const graph = builder.compile();

for await (const chunk of await graph.stream({ foo: "foo" })) {
  console.log(chunk);
}

This key is shared with the parent graph state
This key is private to the SubgraphState and is not visible to the parent graph

{ node1: { foo: 'hi! foo' } }
{ node2: { foo: 'hi! foobar' } }

Different state schemas

For more complex systems you might want to define subgraphs that have a completely different schema from the parent graph (no shared keys). For example, you might want to keep a private message history for each of the agents in a multi-agent system. If that’s the case for your application, you need to define a node function that invokes the subgraph. This function needs to transform the input (parent) state to the subgraph state before invoking the subgraph, and transform the results back to the parent state before returning the state update from the node.

import { StateGraph, START } from "@langchain/langgraph";
import { z } from "zod";

const SubgraphState = z.object({
  bar: z.string(),
});

// Subgraph
const subgraphBuilder = new StateGraph(SubgraphState)
  .addNode("subgraphNode1", (state) => {
    return { bar: "hi! " + state.bar };
  })
  .addEdge(START, "subgraphNode1");

const subgraph = subgraphBuilder.compile();

// Parent graph
const State = z.object({
  foo: z.string(),
});

const builder = new StateGraph(State)
  .addNode("node1", async (state) => {
    const subgraphOutput = await subgraph.invoke({ bar: state.foo }); // (1)!
    return { foo: subgraphOutput.bar }; // (2)!
  })
  .addEdge(START, "node1");

const graph = builder.compile();

Transform the state to the subgraph state
Transform response back to the parent state

Full example: different state schemas

import { StateGraph, START } from "@langchain/langgraph";
import { z } from "zod";

// Define subgraph
const SubgraphState = z.object({
  // note that none of these keys are shared with the parent graph state
  bar: z.string(),
  baz: z.string(),
});

const subgraphBuilder = new StateGraph(SubgraphState)
  .addNode("subgraphNode1", (state) => {
    return { baz: "baz" };
  })
  .addNode("subgraphNode2", (state) => {
    return { bar: state.bar + state.baz };
  })
  .addEdge(START, "subgraphNode1")
  .addEdge("subgraphNode1", "subgraphNode2");

const subgraph = subgraphBuilder.compile();

// Define parent graph
const ParentState = z.object({
  foo: z.string(),
});

const builder = new StateGraph(ParentState)
  .addNode("node1", (state) => {
    return { foo: "hi! " + state.foo };
  })
  .addNode("node2", async (state) => {
    const response = await subgraph.invoke({ bar: state.foo }); // (1)!
    return { foo: response.bar }; // (2)!
  })
  .addEdge(START, "node1")
  .addEdge("node1", "node2");

const graph = builder.compile();

for await (const chunk of await graph.stream(
  { foo: "foo" }, 
  { subgraphs: true }
)) {
  console.log(chunk);
}

Transform the state to the subgraph state
Transform response back to the parent state

[[], { node1: { foo: 'hi! foo' } }]
[['node2:9c36dd0f-151a-cb42-cbad-fa2f851f9ab7'], { subgraphNode1: { baz: 'baz' } }]
[['node2:9c36dd0f-151a-cb42-cbad-fa2f851f9ab7'], { subgraphNode2: { bar: 'hi! foobaz' } }]
[[], { node2: { foo: 'hi! foobaz' } }]

Full example: different state schemas (two levels of subgraphs)

This is an example with two levels of subgraphs: parent -> child -> grandchild.

import { StateGraph, START, END } from "@langchain/langgraph";
import { z } from "zod";

// Grandchild graph
const GrandChildState = z.object({
  myGrandchildKey: z.string(),
});

const grandchild = new StateGraph(GrandChildState)
  .addNode("grandchild1", (state) => {
    // NOTE: child or parent keys will not be accessible here
    return { myGrandchildKey: state.myGrandchildKey + ", how are you" };
  })
  .addEdge(START, "grandchild1")
  .addEdge("grandchild1", END);

const grandchildGraph = grandchild.compile();

// Child graph
const ChildState = z.object({
  myChildKey: z.string(),
});

const child = new StateGraph(ChildState)
  .addNode("child1", async (state) => {
    // NOTE: parent or grandchild keys won't be accessible here
    const grandchildGraphInput = { myGrandchildKey: state.myChildKey }; // (1)!
    const grandchildGraphOutput = await grandchildGraph.invoke(grandchildGraphInput);
    return { myChildKey: grandchildGraphOutput.myGrandchildKey + " today?" }; // (2)!
  }) // (3)!
  .addEdge(START, "child1")
  .addEdge("child1", END);

const childGraph = child.compile();

// Parent graph
const ParentState = z.object({
  myKey: z.string(),
});

const parent = new StateGraph(ParentState)
  .addNode("parent1", (state) => {
    // NOTE: child or grandchild keys won't be accessible here
    return { myKey: "hi " + state.myKey };
  })
  .addNode("child", async (state) => {
    const childGraphInput = { myChildKey: state.myKey }; // (4)!
    const childGraphOutput = await childGraph.invoke(childGraphInput);
    return { myKey: childGraphOutput.myChildKey }; // (5)!
  }) // (6)!
  .addNode("parent2", (state) => {
    return { myKey: state.myKey + " bye!" };
  })
  .addEdge(START, "parent1")
  .addEdge("parent1", "child")
  .addEdge("child", "parent2")
  .addEdge("parent2", END);

const parentGraph = parent.compile();

for await (const chunk of await parentGraph.stream(
  { myKey: "Bob" }, 
  { subgraphs: true }
)) {
  console.log(chunk);
}

We’re transforming the state from the child state channels (myChildKey) to the grandchild state channels (myGrandchildKey)
We’re transforming the state from the grandchild state channels (myGrandchildKey) back to the child state channels (myChildKey)
We’re passing a function here instead of just compiled graph (grandchildGraph)
We’re transforming the state from the parent state channels (myKey) to the child state channels (myChildKey)
We’re transforming the state from the child state channels (myChildKey) back to the parent state channels (myKey)
We’re passing a function here instead of just a compiled graph (childGraph)

[[], { parent1: { myKey: 'hi Bob' } }]
[['child:2e26e9ce-602f-862c-aa66-1ea5a4655e3b', 'child1:781bb3b1-3971-84ce-810b-acf819a03f9c'], { grandchild1: { myGrandchildKey: 'hi Bob, how are you' } }]
[['child:2e26e9ce-602f-862c-aa66-1ea5a4655e3b'], { child1: { myChildKey: 'hi Bob, how are you today?' } }]
[[], { child: { myKey: 'hi Bob, how are you today?' } }]
[[], { parent2: { myKey: 'hi Bob, how are you today? bye!' } }]

Add persistence

You only need to provide the checkpointer when compiling the parent graph. LangGraph will automatically propagate the checkpointer to the child subgraphs.

import { StateGraph, START, MemorySaver } from "@langchain/langgraph";
import { z } from "zod";

const State = z.object({
  foo: z.string(),
});

// Subgraph
const subgraphBuilder = new StateGraph(State)
  .addNode("subgraphNode1", (state) => {
    return { foo: state.foo + "bar" };
  })
  .addEdge(START, "subgraphNode1");

const subgraph = subgraphBuilder.compile();

// Parent graph
const builder = new StateGraph(State)
  .addNode("node1", subgraph)
  .addEdge(START, "node1");

const checkpointer = new MemorySaver();
const graph = builder.compile({ checkpointer });

If you want the subgraph to have its own memory, you can compile it with the appropriate checkpointer option. This is useful in multi-agent systems, if you want agents to keep track of their internal message histories:

const subgraphBuilder = new StateGraph(...)
const subgraph = subgraphBuilder.compile({ checkpointer: true });

View subgraph state

When you enable persistence, you can inspect the graph state (checkpoint) via the appropriate method. To view the subgraph state, you can use the subgraphs option. You can inspect the graph state via graph.getState(config). To view the subgraph state, you can use graph.getState(config, { subgraphs: true }).

Available only when interrupted Subgraph state can only be viewed when the subgraph is interrupted. Once you resume the graph, you won’t be able to access the subgraph state.

View interrupted subgraph state

import { StateGraph, START, MemorySaver, interrupt, Command } from "@langchain/langgraph";
import { z } from "zod";

const State = z.object({
  foo: z.string(),
});

// Subgraph
const subgraphBuilder = new StateGraph(State)
  .addNode("subgraphNode1", (state) => {
    const value = interrupt("Provide value:");
    return { foo: state.foo + value };
  })
  .addEdge(START, "subgraphNode1");

const subgraph = subgraphBuilder.compile();

// Parent graph
const builder = new StateGraph(State)
  .addNode("node1", subgraph)
  .addEdge(START, "node1");

const checkpointer = new MemorySaver();
const graph = builder.compile({ checkpointer });

const config = { configurable: { thread_id: "1" } };

await graph.invoke({ foo: "" }, config);
const parentState = await graph.getState(config);
const subgraphState = (await graph.getState(config, { subgraphs: true })).tasks[0].state; // (1)!

// resume the subgraph
await graph.invoke(new Command({ resume: "bar" }), config);

This will be available only when the subgraph is interrupted. Once you resume the graph, you won’t be able to access the subgraph state.

Stream subgraph outputs

To include outputs from subgraphs in the streamed outputs, you can set the subgraphs option in the stream method of the parent graph. This will stream outputs from both the parent graph and any subgraphs.

for await (const chunk of await graph.stream(
  { foo: "foo" },
  {
    subgraphs: true, // (1)!
    streamMode: "updates",
  }
)) {
  console.log(chunk);
}

Set subgraphs: true to stream outputs from subgraphs.

Stream from subgraphs

import { StateGraph, START } from "@langchain/langgraph";
import { z } from "zod";

// Define subgraph
const SubgraphState = z.object({
  foo: z.string(),
  bar: z.string(),
});

const subgraphBuilder = new StateGraph(SubgraphState)
  .addNode("subgraphNode1", (state) => {
    return { bar: "bar" };
  })
  .addNode("subgraphNode2", (state) => {
    // note that this node is using a state key ('bar') that is only available in the subgraph
    // and is sending update on the shared state key ('foo')
    return { foo: state.foo + state.bar };
  })
  .addEdge(START, "subgraphNode1")
  .addEdge("subgraphNode1", "subgraphNode2");

const subgraph = subgraphBuilder.compile();

// Define parent graph
const ParentState = z.object({
  foo: z.string(),
});

const builder = new StateGraph(ParentState)
  .addNode("node1", (state) => {
    return { foo: "hi! " + state.foo };
  })
  .addNode("node2", subgraph)
  .addEdge(START, "node1")
  .addEdge("node1", "node2");

const graph = builder.compile();

for await (const chunk of await graph.stream(
  { foo: "foo" },
  {
    streamMode: "updates",
    subgraphs: true, // (1)!
  }
)) {
  console.log(chunk);
}

Set subgraphs: true to stream outputs from subgraphs.

[[], { node1: { foo: 'hi! foo' } }]
[['node2:e58e5673-a661-ebb0-70d4-e298a7fc28b7'], { subgraphNode1: { bar: 'bar' } }]
[['node2:e58e5673-a661-ebb0-70d4-e298a7fc28b7'], { subgraphNode2: { foo: 'hi! foobar' } }]
[[], { node2: { foo: 'hi! foobar' } }]

Capabilities

Run and debug

LangGraph APIs

Setup

Shared state schemas

Different state schemas

Add persistence

View subgraph state

Stream subgraph outputs

Capabilities

Run and debug

LangGraph APIs

​Setup

​Shared state schemas

​Different state schemas

​Add persistence

​View subgraph state

​Stream subgraph outputs

Setup

Shared state schemas

Different state schemas

Add persistence

View subgraph state

Stream subgraph outputs