Graph execution - Docs by LangChain

LangGraph agents aren’t black boxes. Every graph is composed of named nodes that execute in sequence or in parallel: classify, research, analyze, synthesize. Graph execution cards make this pipeline visible by rendering a card for each node, showing its status, streaming its content in real time, and tracking completion across the entire workflow. Users see exactly what the agent is doing, which step it’s on, and what each step produced. This pattern is especially useful for production agents because it turns graph structure into product UX. Instead of treating the run as a single assistant response, you can expose the same checkpoints, node names, state keys, and stream metadata that LangGraph uses internally.

How graph nodes map to UI cards

A LangGraph graph defines a series of nodes, each responsible for a specific task. For example, a research pipeline might have:

Classify: categorize the user’s query
Research: gather relevant information
Analyze: draw conclusions from the research
Synthesize: produce a final, polished response

Each node writes its output to a specific key in the graph’s state. On the frontend, you don’t need to hardcode that mapping as useStream discovers each node as it runs via stream.subgraphs and exposes a SubgraphDiscoverySnapshot for every observed step:

// Nodes are discovered automatically — no hardcoded list needed
const graphNodes = [...stream.subgraphs.values()];

// Each snapshot carries the node name and current status
graphNodes.forEach((node) => {
  console.log(node.nodeName, node.status); // "classify", "running"
});

Use node.nodeName for labels in the progress bar and card headers. Pass each snapshot to useMessages(stream, node) to render node-scoped streaming content without coupling the UI to graph state key names. This mapping becomes the contract between your graph and your UI. Backend authors can add, rename, or reorder nodes intentionally, while frontend authors decide how each state key should be visualized: a status badge, markdown panel, table, chart, trace view, or approval card.

Setting up `useStream`

Wire up useStream as usual. The key properties you’ll use are messages (for the conversation) and subgraphs (for the graph nodes discovered in the current run). Pass each discovered subgraph snapshot to a selector to read the messages scoped to that node.

The code examples use useStream<typeof myAgent> for type-safe stream state. See Type inference for Python or JavaScript backends.

import { useStream } from "@langchain/react";

const AGENT_URL = "http://localhost:2024";

export function PipelineChat() {
  const stream = useStream<typeof myAgent>({
    apiUrl: AGENT_URL,
    assistantId: "graph_execution_cards",
  });
  const graphNodes = [...stream.subgraphs.values()];

  return (
    <div>
      <PipelineProgress nodes={graphNodes} isLoading={stream.isLoading} />
      <NodeCardList nodes={graphNodes} stream={stream} isLoading={stream.isLoading} />
    </div>
  );
}

<script setup lang="ts">
import { useStream } from "@langchain/vue";

const AGENT_URL = "http://localhost:2024";

const stream = useStream<typeof myAgent>({
  apiUrl: AGENT_URL,
  assistantId: "graph_execution_cards",
});
</script>

<template>
  <div>
    <PipelineProgress
      :nodes="[...stream.subgraphs.value.values()]"
      :is-loading="stream.isLoading.value"
    />
    <NodeCardList
      :nodes="[...stream.subgraphs.value.values()]"
      :stream="stream"
      :is-loading="stream.isLoading.value"
    />
  </div>
</template>

<script lang="ts">
  import { useStream } from "@langchain/svelte";

  const AGENT_URL = "http://localhost:2024";

  const stream = useStream<typeof myAgent>({
    apiUrl: AGENT_URL,
    assistantId: "graph_execution_cards",
  });
</script>

<div>
  <PipelineProgress nodes={[...stream.subgraphs.values()]} isLoading={stream.isLoading} />
  <NodeCardList
    nodes={[...stream.subgraphs.values()]}
    {stream}
    isLoading={stream.isLoading}
  />
</div>

import { Component, computed } from "@angular/core";
import { injectStream } from "@langchain/angular";

const AGENT_URL = "http://localhost:2024";

@Component({
  selector: "app-pipeline-chat",
  template: `
    <div>
      <app-pipeline-progress
        [nodes]="graphNodes()"
        [isLoading]="stream.isLoading()"
      />
      <app-node-card-list
        [nodes]="graphNodes()"
        [stream]="stream"
        [isLoading]="stream.isLoading()"
      />
    </div>
  `,
})
export class PipelineChatComponent {
  stream = injectStream<typeof myAgent>({
    apiUrl: AGENT_URL,
    assistantId: "graph_execution_cards",
  });

  graphNodes = computed(() => [...this.stream.subgraphs().values()]);
}

Routing streaming tokens to nodes

As the graph streams, each discovered subgraph snapshot identifies the node it belongs to. Pass that snapshot to a selector hook or composable to read the messages scoped to that node:

import { AIMessage } from "langchain";
import { useMessages, type AnyStream, type SubgraphDiscoverySnapshot } from "@langchain/react";

function NodeCard({
  node,
  stream,
}: {
  node: SubgraphDiscoverySnapshot;
  stream: AnyStream;
}) {
  const messages = useMessages(stream, node);
  const lastAIMessage = messages.find(AIMessage.isInstance);
  const streamingContent = lastAIMessage?.text ?? "";

  return <NodeCardBody node={node} content={streamingContent} />;
}

The first mounted selector opens a scoped subscription for that node namespace. When the node card unmounts, the subscription is released automatically.

Determining node status

Each discovered node carries its current status. Use node.status directly; the discovery snapshot reports "pending", "running", "complete", or "error":

type NodeStatus = SubgraphDiscoverySnapshot["status"];

const status: NodeStatus = node.status;

Building the pipeline progress bar

A horizontal progress bar at the top gives users a bird’s-eye view of the entire pipeline. Each step is a labeled segment that fills in as nodes complete:

function PipelineProgress({
  nodes,
  isLoading,
}: {
  nodes: SubgraphDiscoverySnapshot[];
  isLoading: boolean;
}) {
  const firstIncompleteIdx = nodes.findIndex((node) => node.status !== "complete");

  return (
    <div className="flex items-center gap-1">
      {nodes.map((node, i) => {
        const isRunning =
          isLoading && node.status !== "complete" && firstIncompleteIdx === i;
        const colors = {
          pending: "bg-gray-200 text-gray-500",
          running: "bg-blue-400 text-white animate-pulse",
          complete: "bg-green-500 text-white",
          error: "bg-red-500 text-white",
        };
        const status = isRunning ? "running" : node.status;

        return (
          <div key={node.id} className="flex items-center">
            <div
              className={`rounded-full px-3 py-1 text-xs font-medium ${colors[status]}`}
            >
              {node.nodeName}
            </div>
            {i < nodes.length - 1 && (
              <div
                className={`mx-1 h-0.5 w-6 ${
                  status === "complete" ? "bg-green-500" : "bg-gray-200"
                }`}
              />
            )}
          </div>
        );
      })}
    </div>
  );
}

Building collapsible NodeCard components

Each node gets its own card that shows the status badge, content (streaming or final), and a collapsible body for long outputs:

function NodeCard({
  node,
  stream,
}: {
  node: SubgraphDiscoverySnapshot;
  stream: AnyStream;
}) {
  const [open, setOpen] = useState(node.status === "running");
  const messages = useMessages(stream, node);
  const lastAIMessage = messages.find(AIMessage.isInstance);

  useEffect(() => {
    if (node.status === "running") setOpen(true);
    if (node.status === "complete") setOpen(false);
  }, [node.status]);

  return (
    <div className="rounded-lg border bg-white shadow-sm">
      <button
        onClick={() => setOpen(!open)}
        className="flex w-full items-center justify-between p-4"
      >
        <div className="flex items-center gap-3">
          <h3 className="font-semibold">{node.nodeName}</h3>
          <StatusBadge status={node.status} />
        </div>
        <span className={open ? "rotate-90" : ""}>▶</span>
      </button>

      {open && (
        <div className="border-t px-4 py-3">
          <div className="prose prose-sm max-w-none">
            {lastAIMessage?.text?.trim()
              ? <Markdown>{lastAIMessage.text}</Markdown>
              : <p className="italic text-gray-500">Processing...</p>}
          </div>
        </div>
      )}
    </div>
  );
}

Streaming vs. completed content

The node card reads scoped messages for both streaming and final content. This avoids assuming that a graph node name matches the state key it writes to (for example, do_research writes to research in the playground graph):

Source	When to use
`useMessages(stream, node)`	Render node-scoped streaming and final messages
`stream.values`	Read whole-graph state such as the final `synthesis` field, using the actual state key

The pattern is: show the most recent scoped AI message in the node card, and use stream.values only when you intentionally need a graph state field. Because scoped messages are tied to the producing node, the UI can support parallel graph paths without guessing from message order. Each card updates from the stream events that belong to its node, and completed values remain available through stream.values.

function NodeContent({ stream, node }: { stream: AnyStream; node: SubgraphDiscoverySnapshot }) {
  const messages = useMessages(stream, node);
  const content = messages.find(AIMessage.isInstance)?.text ?? "";

  return <Markdown>{content}</Markdown>;
}

Streaming content may include partial tokens or markdown that hasn’t been fully formed yet. If you render markdown, make sure your renderer handles incomplete syntax gracefully (e.g., an unclosed bold marker **).

Putting it all together

Here’s the full card list that combines routing, status detection, and card rendering:

function NodeCardList({
  nodes,
  stream,
  isLoading,
}: {
  nodes: SubgraphDiscoverySnapshot[];
  stream: AnyStream;
  isLoading: boolean;
}) {
  const firstIncompleteIdx = nodes.findIndex((node) => node.status !== "complete");

  return (
    <div className="space-y-3">
      {nodes.map((node, i) => {
        const isComplete = node.status === "complete";
        const isRunning = isLoading && !isComplete && firstIncompleteIdx === i;
        if (!isComplete && !isRunning) return null;

        return <NodeCard key={node.id} node={node} stream={stream} />;
      })}
    </div>
  );
}

Use cases

Graph execution cards work well for any multi-step pipeline where visibility matters:

Research pipelines: classify → gather sources → analyze → synthesize a report
Content generation: outline → draft → fact-check → edit → publish
Data processing: ingest → validate → transform → aggregate → export
Code generation: understand requirements → plan architecture → write code → review → test
Decision workflows: gather context → evaluate options → score alternatives → recommend

Handling dynamic pipelines

Not all graphs have a fixed set of nodes. Some pipelines add or skip nodes based on the input. The discovery map contains only nodes observed for the current thread:

const activeNodes = [...stream.subgraphs.values()];

This ensures your UI only shows cards for nodes that are relevant to the current execution, avoiding empty placeholder cards.

If your graph has conditional branching (e.g., skip “Research” for simple factual queries), skipped nodes will not appear in stream.subgraphs. Your pipeline progress bar can render discovered nodes only or dim expected nodes that have no matching snapshot.

Best practices

Discover nodes from the stream. Render cards from stream.subgraphs rather than hardcoding expected nodes; conditional or skipped steps won’t appear until they run.
Treat state keys as UI contracts. Decide which graph outputs should be stable enough for the frontend to render, and keep those keys documented next to the graph definition.
Use scoped messages for node cards. They work while a node is streaming and after it completes, without coupling UI cards to state key names.
Auto-collapse completed nodes. In long pipelines, auto-collapse finished cards so users can focus on the currently active step.
Show estimated timing. If you have historical data on how long each node takes, display a time estimate to set user expectations.
Add a global progress indicator. Complement per-node cards with an overall progress bar (e.g., “Step 2 of 4”) at the top of the pipeline view.
Handle errors per node. If a node fails, show the error in its card without collapsing the entire pipeline. Other nodes may still complete successfully.

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​How graph nodes map to UI cards

​Setting up useStream

​Routing streaming tokens to nodes

​Determining node status

​Building the pipeline progress bar

​Building collapsible NodeCard components

​Streaming vs. completed content

​Putting it all together

​Use cases

​Handling dynamic pipelines

​Best practices

How graph nodes map to UI cards

Setting up `useStream`

Routing streaming tokens to nodes

Determining node status

Building the pipeline progress bar

Building collapsible NodeCard components

Streaming vs. completed content

Putting it all together

Use cases

Handling dynamic pipelines

Best practices