Todo List

Not every agent interaction is a chat. Sometimes the agent is executing a multi-step plan — and the best way to show progress is a todo list that updates in real time. The deep agent todo list pattern reads a todos array directly from the agent’s state, rendering each item with its current status as the agent works through its plan. It’s a progress dashboard built on the same useStream hook you use for chat — demonstrating that agent state can power any UI, not just message bubbles.

How it works

In a LangGraph agent, state isn’t limited to messages. You can define custom state keys that hold arbitrary data — in this case, a todos array. As the agent executes its plan, it updates each todo’s status from "pending" to "in_progress" to "completed". The useStream hook exposes these custom state values via stream.values, and your UI renders them reactively. The flow looks like this:

User submits a request
Agent creates a plan and populates todos in its state
Agent begins executing — each todo transitions through pending → in_progress → completed
stream.values.todos updates in real time as the agent progresses
Your UI re-renders the todo list with current statuses

Setting up useStream

No special configuration is needed — just point useStream at your agent and read the todos from stream.values. Define a TypeScript interface matching your agent’s state schema and pass it as a type parameter to useStream for type-safe access to state values, including custom state keys like todos. In the examples below, replace typeof myAgent with your interface name:

import type { BaseMessage } from "@langchain/core/messages";

interface TodoItem {
  title: string;
  status: "pending" | "in_progress" | "completed";
  description?: string;
}

interface AgentState {
  messages: BaseMessage[];
  todos: TodoItem[];
}

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

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

export function TodoAgent() {
  const stream = useStream<typeof myAgent>({
    apiUrl: AGENT_URL,
    assistantId: "deep_agent_todo_list",
  });

  const todos = stream.values?.todos ?? [];

  return (
    <div>
      <TodoList todos={todos} />
      {stream.messages.map((msg) => (
        <Message key={msg.id} message={msg} />
      ))}
    </div>
  );
}

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

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

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

const todos = computed(() => stream.values.value?.todos ?? []);
</script>

<template>
  <div>
    <TodoList :todos="todos" />
    <Message
      v-for="msg in stream.messages.value"
      :key="msg.id"
      :message="msg"
    />
  </div>
</template>

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

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

  const { messages, values, submit } = useStream<typeof myAgent>({
    apiUrl: AGENT_URL,
    assistantId: "deep_agent_todo_list",
  });

  $: todos = $values?.todos ?? [];
</script>

<div>
  <TodoList {todos} />
  {#each $messages as msg (msg.id)}
    <Message message={msg} />
  {/each}
</div>

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

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

@Component({
  selector: "app-todo-agent",
  template: `
    <div>
      <app-todo-list [todos]="todos()" />
      @for (msg of stream.messages(); track msg.id) {
        <app-message [message]="msg" />
      }
    </div>
  `,
})
export class TodoAgentComponent {
  stream = useStream<typeof myAgent>({
    apiUrl: AGENT_URL,
    assistantId: "deep_agent_todo_list",
  });

  todos = computed(() => this.stream.values()?.todos ?? []);
}

The Todo interface

Each todo in the array has a simple structure:

interface Todo {
  status: "pending" | "in_progress" | "completed";
  content: string;
}

Property	Description
`status`	The current state of this task — `pending` (not started), `in_progress` (agent is working on it), `completed` (done)
`content`	A human-readable description of what the task involves

The agent populates this array when it creates its plan, then updates individual items as it executes each step.

Building the TodoList component

The todo list renders each item with a status icon, color coding, and visual styling that reflects the current state:

function TodoList({ todos }: { todos: Todo[] }) {
  const completed = todos.filter((t) => t.status === "completed").length;
  const percentage = todos.length
    ? Math.round((completed / todos.length) * 100)
    : 0;

  return (
    <div className="rounded-lg border bg-white p-4 shadow-sm">
      <div className="mb-4 flex items-center justify-between">
        <h2 className="text-lg font-semibold">Agent Progress</h2>
        <span className="text-sm text-gray-500">
          {completed}/{todos.length} tasks
        </span>
      </div>

      <ProgressBar percentage={percentage} />

      <ul className="mt-4 space-y-2">
        {todos.map((todo, i) => (
          <TodoItem key={i} todo={todo} />
        ))}
      </ul>
    </div>
  );
}

Progress bar

A visual progress bar gives users an at-a-glance summary of overall completion:

function ProgressBar({ percentage }: { percentage: number }) {
  return (
    <div className="space-y-1">
      <div className="flex items-center justify-between text-xs text-gray-500">
        <span>Progress</span>
        <span>{percentage}%</span>
      </div>
      <div className="h-2 overflow-hidden rounded-full bg-gray-200">
        <div
          className="h-full rounded-full bg-green-500 transition-all duration-500"
          style={{ width: `${percentage}%` }}
        />
      </div>
    </div>
  );
}

Individual todo items

Each item gets a status icon, color-coded text, and strikethrough styling for completed tasks:

function TodoItem({ todo }: { todo: Todo }) {
  const config = {
    pending: {
      icon: "○",
      textClass: "text-gray-600",
      bgClass: "bg-gray-50",
      iconClass: "text-gray-400",
    },
    in_progress: {
      icon: "◉",
      textClass: "text-amber-800",
      bgClass: "bg-amber-50 border-amber-200",
      iconClass: "text-amber-500 animate-pulse",
    },
    completed: {
      icon: "✓",
      textClass: "text-green-800 line-through",
      bgClass: "bg-green-50 border-green-200",
      iconClass: "text-green-500",
    },
  };

  const style = config[todo.status];

  return (
    <li
      className={`flex items-start gap-3 rounded-md border px-3 py-2 ${style.bgClass}`}
    >
      <span className={`mt-0.5 text-lg leading-none ${style.iconClass}`}>
        {style.icon}
      </span>
      <span className={`text-sm ${style.textClass}`}>{todo.content}</span>
    </li>
  );
}

The in_progress icon uses animate-pulse to draw attention to the currently active task.

Calculating progress

Derive progress metrics directly from the todos array:

const todos = stream.values?.todos ?? [];

const completed = todos.filter((t) => t.status === "completed").length;
const inProgress = todos.filter((t) => t.status === "in_progress").length;
const pending = todos.filter((t) => t.status === "pending").length;
const percentage = todos.length
  ? Math.round((completed / todos.length) * 100)
  : 0;

These values update reactively as the agent modifies its state, keeping the progress bar and counters in sync.

Combining with chat messages

The todo list works alongside the regular chat interface. A practical layout shows the todo list as a persistent sidebar or header panel, with chat messages below:

function TodoAgentLayout() {
  const stream = useStream<typeof myAgent>({
    apiUrl: AGENT_URL,
    assistantId: "deep_agent_todo_list",
  });

  const todos = stream.values?.todos ?? [];

  return (
    <div className="flex h-screen flex-col">
      {todos.length > 0 && (
        <div className="border-b bg-gray-50 p-4">
          <TodoList todos={todos} />
        </div>
      )}

      <main className="flex-1 overflow-y-auto p-6">
        <div className="mx-auto max-w-2xl space-y-4">
          {stream.messages.map((msg) => (
            <Message key={msg.id} message={msg} />
          ))}
        </div>
      </main>

      <ChatInput
        onSubmit={(text) =>
          stream.submit({ messages: [{ type: "human", content: text }] })
        }
        isLoading={stream.isLoading}
      />
    </div>
  );
}

Show the todo list only when todos.length > 0. Before the agent creates its plan, there’s nothing to display — and showing an empty component wastes space.

Custom state beyond todos

This pattern demonstrates a powerful principle: stream.values can expose any custom state your agent defines, not just messages. The todos array is just one example. You could use the same approach for:

Progress metrics — stream.values.progress with numeric completion data
Generated artifacts — stream.values.document with a structured document the agent is building
Decision logs — stream.values.decisions tracking every choice the agent made
Resource lists — stream.values.sources with links and references the agent found

// Any custom state key your agent defines is accessible
const document = stream.values?.document;
const sources = stream.values?.sources ?? [];
const confidence = stream.values?.confidence_score;

Custom state keys are defined in your LangGraph graph’s state schema. The useStream hook automatically includes them in stream.values — no additional client-side configuration is needed.

Animating transitions

Todo status transitions happen in real time, and smooth animations make these changes feel polished rather than jarring:

function TodoItem({ todo }: { todo: Todo }) {
  return (
    <li
      className={`
        flex items-start gap-3 rounded-md border px-3 py-2
        transition-all duration-300 ease-in-out
        ${getStatusStyles(todo.status)}
      `}
    >
      <span
        className={`
          mt-0.5 text-lg leading-none transition-colors duration-300
          ${getIconStyles(todo.status)}
        `}
      >
        {getStatusIcon(todo.status)}
      </span>
      <span
        className={`
          text-sm transition-all duration-300
          ${todo.status === "completed" ? "line-through opacity-60" : ""}
        `}
      >
        {todo.content}
      </span>
    </li>
  );
}

The transition-all duration-300 classes ensure that color changes, strikethrough, and opacity shifts all animate smoothly.

Use cases

The todo list pattern fits any scenario where an agent executes a structured plan:

Project planning — agent breaks a project into tasks and works through them sequentially
Research workflows — each research question becomes a todo that the agent investigates and completes
Data processing — steps like ingestion, validation, transformation, and export each get their own todo
Onboarding flows — agent walks through setup steps, checking off each one as it configures services
Report generation — sections of a report become todos: gather data, analyze trends, write summary, format output

Handling empty and loading states

Handle the initial state before the agent has created its plan:

function TodoList({ todos, isLoading }: { todos: Todo[]; isLoading: boolean }) {
  if (todos.length === 0 && !isLoading) {
    return null;
  }

  if (todos.length === 0 && isLoading) {
    return (
      <div className="rounded-lg border bg-white p-4 shadow-sm">
        <div className="flex items-center gap-2 text-sm text-gray-500">
          <span className="animate-spin">⟳</span>
          Agent is creating a plan...
        </div>
      </div>
    );
  }

  return (
    <div className="rounded-lg border bg-white p-4 shadow-sm">
      {/* ... full todo list rendering */}
    </div>
  );
}

Best practices

Show the todo list prominently — it’s the primary progress indicator for plan-based agents. Don’t bury it below the fold.
Animate status transitions — smooth transitions make the agent feel more responsive. Use CSS transitions on background color, text decoration, and opacity.
Only highlight one in_progress item — agents typically work on one task at a time. If multiple items show as in_progress, the UI gets noisy. Consider only pulsing the first one.
Collapse or dim completed items — as the list grows, completed items become less relevant. Reduce their visual weight so users focus on what’s still happening.
Show the progress percentage — a single number like “67% complete” is immediately understandable, even from across the room.
Keep the todo list in sync — because stream.values updates reactively, the todo list stays current automatically. Don’t add manual polling or refresh logic.

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Get started

Core capabilities

Frontend

Protocols

Command line interface

How it works

Setting up useStream

The Todo interface

Building the TodoList component

Progress bar

Individual todo items

Calculating progress

Combining with chat messages

Custom state beyond todos

Animating transitions

Use cases

Handling empty and loading states

Best practices

​How it works

​Setting up useStream

​The Todo interface

​Building the TodoList component

​Progress bar

​Individual todo items

​Calculating progress

​Combining with chat messages

​Custom state beyond todos

​Animating transitions

​Use cases

​Handling empty and loading states

​Best practices

How it works

Setting up useStream

The Todo interface

Building the TodoList component

Progress bar

Individual todo items

Calculating progress

Combining with chat messages

Custom state beyond todos

Animating transitions

Use cases

Handling empty and loading states

Best practices