@langchain/vue

Vue SDK for building AI-powered applications with Deep Agents, LangChain and LangGraph. It provides a useStream composable that manages streaming, state, branching, and interrupts using Vue's reactivity system.

Installation

npm install @langchain/vue @langchain/core

Peer dependencies: vue (^3.0.0), @langchain/core (^1.0.1)

Quick Start

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

const { messages, submit, isLoading } = useStream({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages" :key="msg.id ?? i">
      {{ msg.content }}
    </div>

    <button
      :disabled="isLoading"
      @click="submit({ messages: [{ type: 'human', content: 'Hello!' }] })"
    >
      Send
    </button>
  </div>
</template>

useStream Options

| Option | Type | Description | |---|---|---| | assistantId | string | Required. The assistant/graph ID to stream from. | | apiUrl | string | Base URL of the LangGraph API. | | client | Client | Pre-configured Client instance (alternative to apiUrl). | | messagesKey | string | State key containing messages. Defaults to "messages". | | initialValues | StateType | Initial state values before any stream data arrives. | | fetchStateHistory | boolean \| { limit: number } | Fetch thread history on stream completion. Enables branching. | | throttle | boolean \| number | Throttle state updates for performance. | | onFinish | (state, error?) => void | Called when the stream completes. | | onError | (error, state?) => void | Called on stream errors. | | onThreadId | (threadId) => void | Called when a new thread is created. | | onUpdateEvent | (event) => void | Receive update events from the stream. | | onCustomEvent | (event) => void | Receive custom events from the stream. | | onStop | () => void | Called when the stream is stopped by the user. |

Return Values

All reactive properties are Vue computed or ref values that auto-unwrap in <template> blocks — use them directly (e.g. messages, not messages.value). The queue object is reactive, so its nested properties also auto-unwrap in templates.

| Property | Type | Description | |---|---|---| | values | ComputedRef<StateType> | Current graph state. | | messages | ComputedRef<Message[]> | Messages from the current state. | | isLoading | Ref<boolean> | Whether a stream is currently active. | | error | ComputedRef<unknown> | The most recent error, if any. | | interrupt | ComputedRef<Interrupt \| undefined> | Current interrupt requiring user input. | | branch | Ref<string> | Active branch identifier. | | submit(values, options?) | function | Submit new input to the graph. When called while a stream is active, the run is created on the server with multitaskStrategy: "enqueue" and queued automatically. | | stop() | function | Cancel the active stream. | | setBranch(branch) | function | Switch to a different conversation branch. | | getMessagesMetadata(msg, index?) | function | Get branching and checkpoint metadata for a message. | | switchThread(id) | (id: string \| null) => void | Switch to a different thread. Pass null to start a new thread on next submit. | | queue.entries | ReadonlyArray<QueueEntry> | Pending server-side runs. Each entry has id (server run ID), values, options, and createdAt. | | queue.size | number | Number of pending runs on the server. | | queue.cancel(id) | (id: string) => Promise<boolean> | Cancel a pending run on the server by its run ID. | | queue.clear() | () => Promise<void> | Cancel all pending runs on the server. |

Type Safety

Provide your state type as a generic parameter:

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

interface MyState {
  messages: BaseMessage[];
  context?: string;
}

const { messages, submit } = useStream<MyState>({
  assistantId: "my-graph",
  apiUrl: "http://localhost:2024",
});
</script>

Typed Interrupts

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

const { interrupt, submit } = useStream<
  { messages: BaseMessage[] },
  { InterruptType: { question: string } }
>({
  assistantId: "my-graph",
  apiUrl: "http://localhost:2024",
});
</script>

Handling Interrupts

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

const { messages, interrupt, submit } = useStream<
  { messages: BaseMessage[] },
  { InterruptType: { question: string } }
>({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages" :key="msg.id ?? i">
      {{ msg.content }}
    </div>

    <div v-if="interrupt">
      <p>{{ interrupt.value.question }}</p>
      <button @click="submit(null, { command: { resume: 'Approved' } })">
        Approve
      </button>
    </div>

    <button
      @click="submit({ messages: [{ type: 'human', content: 'Hello' }] })"
    >
      Send
    </button>
  </div>
</template>

Branching

Enable conversation branching with fetchStateHistory: true:

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

const { messages, submit, getMessagesMetadata, setBranch } = useStream({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
  fetchStateHistory: true,
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages" :key="msg.id ?? i">
      <p>{{ msg.content }}</p>

      <template v-if="getMessagesMetadata(msg, i)?.branchOptions">
        <button
          @click="() => {
            const meta = getMessagesMetadata(msg, i);
            const prev = meta.branchOptions[meta.branchOptions.indexOf(meta.branch) - 1];
            if (prev) setBranch(prev);
          }"
        >
          Previous
        </button>
        <button
          @click="() => {
            const meta = getMessagesMetadata(msg, i);
            const next = meta.branchOptions[meta.branchOptions.indexOf(meta.branch) + 1];
            if (next) setBranch(next);
          }"
        >
          Next
        </button>
      </template>
    </div>

    <button
      @click="submit({ messages: [{ type: 'human', content: 'Hello' }] })"
    >
      Send
    </button>
  </div>
</template>

Server-Side Queuing

When submit() is called while a stream is already active, the SDK automatically creates the run on the server with multitaskStrategy: "enqueue". The pending runs are tracked in queue and processed in order as each finishes:

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

const { messages, submit, isLoading, queue, switchThread } = useStream({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages" :key="msg.id ?? i">
      {{ msg.content }}
    </div>

    <div v-if="queue.size > 0">
      <p>{{ queue.size }} message(s) queued</p>
      <button @click="queue.clear()">Clear Queue</button>
    </div>

    <button
      :disabled="isLoading"
      @click="submit({ messages: [{ type: 'human', content: 'Hello!' }] })"
    >
      Send
    </button>
    <button @click="switchThread(null)">New Thread</button>
  </div>
</template>

Switching threads via switchThread() cancels all pending runs and clears the queue.

Custom Transport

Instead of connecting to a LangGraph API, you can provide your own streaming transport. Pass a transport object instead of assistantId to use a custom backend:

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

const {
  messages,
  submit,
  isLoading,
  branch,
  setBranch,
  getMessagesMetadata,
} = useStream<{ messages: BaseMessage[] }>({
  transport: new FetchStreamTransport({
    url: "https://my-api.example.com/stream",
  }),
  threadId: null,
  onThreadId: (id) => console.log("Thread created:", id),
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages" :key="msg.id ?? i">
      <p>{{ msg.content }}</p>
      <span v-if="getMessagesMetadata(msg, i)?.streamMetadata">
        Node: {{ getMessagesMetadata(msg, i)?.streamMetadata?.langgraph_node }}
      </span>
    </div>

    <p>Current branch: {{ branch }}</p>

    <button
      :disabled="isLoading"
      @click="submit({ messages: [{ type: 'human', content: 'Hello!' }] })"
    >
      Send
    </button>
  </div>
</template>

The custom transport interface returns the same properties as the standard useStream composable, including getMessagesMetadata, branch, setBranch, switchThread, and all message/interrupt/subagent helpers. When using a custom transport, getMessagesMetadata returns stream metadata sent alongside messages during streaming; branch and setBranch provide local branch state management. onFinish is also supported and receives a synthetic ThreadState built from the final locally streamed values; the run metadata argument is undefined.

Sharing State with provideStream

When multiple components need access to the same stream (a message list, a header, an input bar), use provideStream and useStreamContext to share a single stream instance via Vue's provide/inject:

<!-- ChatContainer.vue -->
<script setup lang="ts">
import { provideStream } from "@langchain/vue";

provideStream({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
});
</script>

<template>
  <ChatHeader />
  <MessageList />
  <MessageInput />
</template>

<!-- MessageList.vue -->
<script setup lang="ts">
import { useStreamContext } from "@langchain/vue";

const { messages } = useStreamContext();
</script>

<template>
  <div v-for="(msg, i) in messages.value" :key="msg.id ?? i">
    {{ msg.content }}
  </div>
</template>

<!-- MessageInput.vue -->
<script setup lang="ts">
import { useStreamContext } from "@langchain/vue";
import { ref } from "vue";

const { submit, isLoading } = useStreamContext();
const input = ref("");

function send() {
  submit({ messages: [{ type: "human", content: input.value }] });
  input.value = "";
}
</script>

<template>
  <form @submit.prevent="send">
    <textarea v-model="input" />
    <button :disabled="isLoading.value" type="submit">Send</button>
  </form>
</template>

App-Level Configuration with LangChainPlugin

Use the Vue plugin to set default configuration for all useStream calls:

import { createApp } from "vue";
import { LangChainPlugin } from "@langchain/vue";
import App from "./App.vue";

const app = createApp(App);
app.use(LangChainPlugin, {
  apiUrl: "http://localhost:2024",
});
app.mount("#app");

Then in any component, apiUrl is inherited automatically:

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

const stream = useStream({ assistantId: "agent" });
</script>

Multiple Agents

Nest provideStream calls for multi-agent scenarios — Vue's provide/inject scoping ensures each subtree gets its own stream:

<!-- ResearchPanel.vue -->
<script setup lang="ts">
import { provideStream } from "@langchain/vue";
provideStream({ assistantId: "researcher", apiUrl: "http://localhost:2024" });
</script>

<template>
  <MessageList />
  <MessageInput />
</template>

Playground

For complete end-to-end examples with full agentic UIs, visit the LangChain UI Playground.

License

MIT