@chat-adapter/web

@chat-adapter/web

npm package: @chat-adapter/web

Web adapter for Chat SDK. Lets a chat-sdk bot serve a browser chat UI alongside Slack, Teams, Discord, etc. — the same bot.onDirectMessage(...) handler fires for every platform.

The adapter speaks the AI SDK UI message stream protocol by default, so React, Vue, and Svelte AI SDK clients work against the server endpoint. Set protocol: "ag-ui" to speak AG-UI instead, for TanStack AI and other AG-UI clients. The server has no runtime dependency on either client SDK.

Documentation: chat-sdk.dev/adapters/official/web · Guides: vercel.com/kb/chat-sdk

Installation

pnpm add @chat-adapter/web

Then install the client packages that match your UI:

Scaffold with the CLI

To scaffold a new browser chat bot with the Web adapter preselected:

npx create-chat-sdk@latest my-bot --adapter web memory

Visit the adapters directory to see other available official and vendor-official adapters.

Quick start

Server

// lib/bot.ts
import { Chat } from "chat";
import { createWebAdapter } from "@chat-adapter/web";
import { createMemoryState } from "@chat-adapter/state-memory";

export const bot = new Chat({
  userName: "mybot",
  adapters: {
    web: createWebAdapter({
      userName: "mybot",
      getUser: (req) => ({ id: getUserIdFromCookie(req) }),
    }),
  },
  state: createMemoryState(),
});

bot.onDirectMessage(async (thread, message) => {
  await thread.post(`You said: ${message.text}`);
});

// app/api/chat/route.ts
import { after } from "next/server";
import { bot } from "@/lib/bot";

export async function POST(request: Request): Promise<Response> {
  return bot.webhooks.web(request, {
    waitUntil: (task) => after(() => task),
  });
}

Client

React

// app/chat/page.tsx
"use client";
import { useChat } from "@chat-adapter/web/react";

export default function ChatPage() {
  const { messages, sendMessage, status, stop } = useChat();
  // Render with `ai-elements` (<Conversation>, <Message>, <PromptInput>)
  // or your own components — `messages`, `sendMessage`, `status` are the
  // standard `@ai-sdk/react` API.
}

Vue

<!-- components/Chat.vue -->
<script setup lang="ts">
import { useChat } from "@chat-adapter/web/vue";

const chat = useChat({ api: "/api/chat" });
</script>

<template>
  <div v-for="msg in chat.messages" :key="msg.id">
    <template
      v-for="(part, index) in msg.parts"
      :key="`${msg.id}-${part.type}-${index}`"
    >
      <p v-if="part.type === 'text'">{{ part.text }}</p>
    </template>
  </div>
</template>

Svelte

<!-- Chat.svelte -->
<script lang="ts">
  import { useChat } from "@chat-adapter/web/svelte";

  const chat = useChat({ api: "/api/chat" });
</script>

{#each chat.messages as msg (msg.id)}
  {#each msg.parts as part, index (`${msg.id}-${part.type}-${index}`)}
    {#if part.type === "text"}<p>{part.text}</p>{/if}
  {/each}
{/each}

TanStack AI

Set protocol: "ag-ui" on the adapter, then point TanStack AI's useChat at the route with fetchServerSentEvents:

createWebAdapter({
  userName: "mybot",
  getUser: (req) => ({ id: getUserIdFromCookie(req) }),
  protocol: "ag-ui",
});

// app/chat/page.tsx
"use client";
import { fetchServerSentEvents, useChat } from "@tanstack/ai-react";

export default function ChatPage() {
  const { messages, sendMessage, isLoading, stop } = useChat({
    connection: fetchServerSentEvents("/api/chat"),
    threadId: "support-1",
  });
  // Text parts carry their text in `part.content`.
}

threadId becomes the conversation id in the chat-sdk thread id. Each thread.post call arrives as its own assistant message, and handler errors end the run with a RUN_ERROR event.

Authentication

getUser is the security boundary for the Web adapter. Unlike Slack/Teams where the platform signs every webhook, web requests come straight from a browser — you must identify the caller yourself. Returning null causes the adapter to respond with HTTP 401 and no handler runs.

Plug in whatever your app already uses:

// NextAuth
createWebAdapter({
  userName: "mybot",
  getUser: async (req) => {
    const session = await getServerSession(authOptions);
    if (!session?.user) return null;
    return { id: session.user.id, name: session.user.name };
  },
});

// Clerk
createWebAdapter({
  userName: "mybot",
  getUser: async (req) => {
    const { userId, sessionClaims } = await auth();
    if (!userId) return null;
    return { id: userId, name: sessionClaims?.name as string | undefined };
  },
});

// Custom session cookie
createWebAdapter({
  userName: "mybot",
  getUser: async (req) => {
    const sessionId = req.headers.get("cookie")?.match(/session=([^;]+)/)?.[1];
    if (!sessionId) return null;
    const user = await db.users.findBySession(sessionId);
    return user ? { id: user.id, name: user.name } : null;
  },
});

If getUser throws, the adapter returns 401 and logs the error. Don't include sensitive data in the error message — it's not surfaced to the client, but it is logged.

The resolved user.id is embedded in the chat-sdk thread id (see Threading below). User ids containing : are rejected with HTTP 400 because they would corrupt the round-trip through decodeThreadId. If your auth provider emits ids with colons (e.g. provider:sub claims), normalize them inside getUser — for example by base64-encoding.

Threading

By default, each useChat conversation maps to one chat-sdk thread:

web:{user.id}:{conversationId}

conversationId is the id field AI SDK's useChat sends in its request body, or the threadId field with protocol: "ag-ui". If your client supplies one (useChat({ id: "support-chat" })), it's reused across reloads; otherwise a fresh id is generated per request. A conversation id that isn't a string, or that contains :, is rejected with HTTP 400.

channel.messages and thread.messages are equivalent on web — the channel id is the thread id. This avoids cross-conversation bleed when persistMessageHistory is enabled and the same user has multiple useChat conversations open.

To override (for example, one thread per user regardless of conversation):

createWebAdapter({
  userName: "mybot",
  getUser: (req) => /* ... */,
  threadIdFor: ({ user }) => `web:${user.id}:default`,
});

The encode/decode helpers are exposed on the adapter:

adapter.encodeThreadId({ userId: "u1", conversationId: "abc" });
// → "web:u1:abc"
adapter.decodeThreadId("web:u1:abc");
// → { userId: "u1", conversationId: "abc" }

Streaming

thread.post accepts an AsyncIterable<string | StreamChunk> and pumps deltas straight onto the SSE response body — no edit loop, no rate limiting. Handlers can use any model library. For example, with the AI SDK's streamText:

import { streamText } from "ai";
// Bring your own model from any AI SDK provider
// (@ai-sdk/openai, @ai-sdk/anthropic, @ai-sdk/google, ...).

bot.onDirectMessage(async (thread, message) => {
  const result = streamText({
    model: myModel,
    prompt: message.text,
  });
  await thread.post(result.textStream);
});

The adapter honors request.signal, so calling stop() from the client short-circuits the iterator on the server. task_update and plan_update StreamChunks have no native v1 representation on the wire and are dropped silently.

Message persistence

persistMessageHistory defaults to true. Web has no platform-side history API, so the only way for chat-sdk handlers to see prior turns via thread.messages / channel.messages is through the configured state adapter's message history cache. Set it to false only if your handler doesn't need prior turns:

createWebAdapter({
  userName: "mybot",
  getUser: (req) => /* ... */,
  persistMessageHistory: false,
});

The client resends the whole conversation on every request, but the adapter doesn't read history from it. A browser controls the request body's messages[] array, so the adapter consumes only the latest user message and strips tool parts from it. The last entry must be a user message; a body ending in an assistant or tool message, such as a client-side tool result, is rejected with HTTP 400. Sending the same user message again (regenerate() or a reload) runs the handler again rather than being dropped as a duplicate, and history keeps the earlier reply and stores the repeated message a second time.

message.raw is typed WebMessage. Part fields other than type are unknown. With "ai-sdk" the shape matches the AI SDK UIMessage, so you can cast it with message.raw as UIMessage.

Framework helpers

@chat-adapter/web/react exports a thin wrapper around @ai-sdk/react's useChat preconfigured with DefaultChatTransport:

import { useChat } from "@chat-adapter/web/react";

const { messages, sendMessage, status, stop, regenerate } = useChat({
  api: "/api/chat",        // default
  threadId: "support-1",   // becomes useChat's `id` and the request body's `id`
});

For advanced configuration (custom transport, response interceptors, etc.) use @ai-sdk/react's useChat directly — there's nothing magical in the wrapper.

@chat-adapter/web/vue exports a useChat factory that returns a Vue-reactive Chat instance from @ai-sdk/vue:

<script setup lang="ts">
import { useChat } from "@chat-adapter/web/vue";

const chat = useChat({ api: "/api/chat", threadId: "support-1" });
</script>

<template>
  <div v-for="msg in chat.messages" :key="msg.id">
    <template
      v-for="(part, index) in msg.parts"
      :key="`${msg.id}-${part.type}-${index}`"
    >
      <p v-if="part.type === 'text'">{{ part.text }}</p>
    </template>
  </div>
</template>

@chat-adapter/web/svelte exports a useChat factory that returns a Svelte-reactive Chat instance from @ai-sdk/svelte:

<script lang="ts">
  import { useChat } from "@chat-adapter/web/svelte";

  const chat = useChat({ api: "/api/chat", threadId: "support-1" });
</script>

{#each chat.messages as msg (msg.id)}
  {#each msg.parts as part, index (`${msg.id}-${part.type}-${index}`)}
    {#if part.type === "text"}<p>{part.text}</p>{/if}
  {/each}
{/each}

Unlike the React helper, Vue and Svelte return the Chat instance directly. Access chat.messages, chat.sendMessage(), chat.status, and chat.stop() on that object instead of destructuring.

Configuration

Features

Messaging

Rich content

Conversations

Message history

v1 scope

In: text + markdown, native streaming, DM-style routing, persisted message history, abort propagation via request.signal.

Out (deferred to v2): cards/JSX rendering, reactions, modals, file uploads, edit/delete, multi-tab proactive push.

Troubleshooting

Every request returns 401

• getUser is returning null or throwing. Add a log inside it to confirm the request actually carries the session you expect.
• Cookies aren't being forwarded — check that useChat is mounted on the same origin as /api/chat (or that your transport passes credentials).

Every request returns 400 "Invalid user id"

• The id returned by getUser contains a : character, which would corrupt the thread-id round-trip. Normalize the id inside getUser (for example, id.replace(/:/g, "_") or base64-encode it).

useChat recreates state on every render

• Don't pass id: undefined to useChat. The wrapper guards against this internally — but if you're calling @ai-sdk/react's useChat directly, omit id rather than passing undefined.

thread.messages is empty

• persistMessageHistory is false and there is no platform-side history to fall back on. Set it to true (the default). The adapter never passes the request body's messages[] to handlers, so the state adapter is the only source of prior turns.

Requests return 400 "The last entry in messages must be a user message"

• The adapter only handles new user turns. Client-side tool results and automatic resubmits (for example, useChat's sendAutomaticallyWhen) send a body ending in an assistant or tool message, which isn't supported.

AI Coding Agents

If you use an AI coding agent such as OpenAI Codex, Claude Code, or Cursor, install the Chat SDK skill so it knows the SDK APIs, adapter patterns, and project conventions before writing code.

npx skills add vercel/chat

The skill references bundled documentation in node_modules/chat/docs, plus adapter guides and starter templates in the published package.

You can also install the Vercel Plugin for a broader agent toolkit — it includes the Chat SDK skill alongside specialist agents, agent slash commands, and more:

npx plugins add vercel/vercel-plugin

The plugin is optional; the skill alone is enough to build with Chat SDK.

For agent-readable documentation, see chat-sdk.dev/llms.txt (page index) or chat-sdk.dev/llms-full.txt (full text).

License

MIT