> ## Documentation Index
> Fetch the complete documentation index at: https://sunpeak.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# MCP Apps sendMessage - Send Chat Messages

> Send a message from an MCP App View to the host's chat interface. Inject user-role messages with text, images, or other content blocks into the conversation.

<Badge color="green">MCP Apps SDK</Badge>

```ts theme={null}
import { App } from "@modelcontextprotocol/ext-apps";
```

## Overview

`sendMessage` sends a message from the View into the host's chat interface, appearing as if the user typed it. This enables the app to drive the conversation -- for example, submitting a user selection, asking a follow-up question, or triggering the model to act on data displayed in the UI.

The message is always sent with `role: "user"`. The host may reject the message (for example, if sending is rate-limited or disabled), in which case `isError` will be `true` in the response.

## Signature

```ts theme={null}
async sendMessage(
  params: { role: "user"; content: ContentBlock[] },
  options?: RequestOptions,
): Promise<{ isError?: boolean }>
```

## Parameters

<ResponseField name="params" type="object" required>
  The message parameters.

  <ResponseField name="role" type="&#x22;user&#x22;" required>
    The message role. Currently only `"user"` is supported.
  </ResponseField>

  <ResponseField name="content" type="ContentBlock[]" required>
    Array of content blocks to include in the message. Supports text, images, and other standard MCP content block types.
  </ResponseField>
</ResponseField>

<ResponseField name="options" type="RequestOptions">
  Optional request configuration.

  <ResponseField name="signal" type="AbortSignal">
    An `AbortSignal` to cancel the request.
  </ResponseField>
</ResponseField>

## Returns

<ResponseField name="result" type="object">
  <ResponseField name="isError" type="boolean">
    `true` if the host rejected the message. When absent or `false`, the message was accepted.
  </ResponseField>
</ResponseField>

## Usage

### Send a text message

```ts theme={null}
const result = await app.sendMessage({
  role: "user",
  content: [{ type: "text", text: "Show me details for item #42" }],
});

if (result.isError) {
  console.error("Host rejected the message");
}
```

### Send a message based on user interaction

```ts theme={null}
function onItemSelected(itemId: string) {
  app.sendMessage({
    role: "user",
    content: [{
      type: "text",
      text: `Tell me more about ${itemId}`,
    }],
  });
}
```

### Combine with updateModelContext for large payloads

When you need to send a large amount of data along with a message, offload the data to model context first, then send a brief trigger message:

```ts theme={null}
await app.updateModelContext({
  content: [{ type: "text", text: fullTranscript }],
});
await app.sendMessage({
  role: "user",
  content: [{ type: "text", text: "Summarize the key points" }],
});
```

## Related

* [Requests overview](/mcp-apps/app/requests) -- all available View-to-host request methods
* [`useSendMessage`](/app-framework/hooks/use-send-message) -- sunpeak React convenience hook
* [updateModelContext](/mcp-apps/app/requests/update-model-context) -- set model context without triggering a response