Channels reference changedchannels-reference

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# Channels reference

> Build an MCP server that pushes webhooks, alerts, and chat messages into a Claude Code session. Reference for the channel contract: capability declaration, notification events, reply tools, sender gating, and permission relay.

<Note>
  Channels are in [research preview](/docs/en/channels#research-preview). Team and Enterprise organizations must [explicitly enable them](/docs/en/channels#enterprise-controls).
</Note>

A channel is an MCP server that pushes events into a Claude Code session so Claude can react to things happening outside the terminal.

You can build a one-way or two-way channel. One-way channels forward alerts, webhooks, or monitoring events for Claude to act on. Two-way channels like chat bridges also [expose a reply tool](#expose-a-reply-tool) so Claude can send messages back. A channel with a trusted sender path can also opt in to [relay permission prompts](#relay-permission-prompts) so you can approve or deny tool use remotely.

This page covers:

* [Overview](#overview): how channels work
* [What you need](#what-you-need): requirements and general steps
* [Example: build a webhook receiver](#example-build-a-webhook-receiver): a minimal one-way walkthrough
* [Server options](#server-options): the constructor fields
* [Notification format](#notification-format): the event payload and delivery behavior
* [Expose a reply tool](#expose-a-reply-tool): let Claude send messages back
* [Gate inbound messages](#gate-inbound-messages): sender checks to prevent prompt injection
* [Relay permission prompts](#relay-permission-prompts): forward tool approval prompts to remote channels

To use an existing channel instead of building one, see [Channels](/docs/en/channels). Telegram, Discord, iMessage, and fakechat are included in the research preview.

## Overview

A channel is an [MCP](https://modelcontextprotocol.io) server that runs on the same machine as Claude Code. Claude Code spawns it as a subprocess and communicates over stdio. Your channel server is the bridge between external systems and the Claude Code session:

* **Chat platforms** (Telegram, Discord): your plugin runs locally and polls the platform's API for new messages. When someone DMs your bot, the plugin receives the message and forwards it to Claude. No URL to expose.
* **Webhooks** (CI, monitoring): your server listens on a local HTTP port. External systems POST to that port, and your server pushes the payload to Claude.

<img src="https://mintcdn.com/claude-code/9FG0ZKj9uKYiHmbi/images/channel-architecture.svg?fit=max&auto=format&n=9FG0ZKj9uKYiHmbi&q=85&s=9a037b7da80184ae49015c0256b21a1f" className="dark:hidden" alt="Architecture diagram showing external systems connecting to your local channel server, which communicates with Claude Code over stdio" width="600" height="220" data-path="images/channel-architecture.svg" />

<img src="https://mintcdn.com/claude-code/_xqph1dUOslCOwsj/images/channel-architecture-dark.svg?fit=max&auto=format&n=_xqph1dUOslCOwsj&q=85&s=ae1e494440806a6a5d74a1279e22e162" className="hidden dark:block" alt="Architecture diagram showing external systems connecting to your local channel server, which communicates with Claude Code over stdio" width="600" height="220" data-path="images/channel-architecture-dark.svg" />

## What you need

The only hard requirement is the [`@modelcontextprotocol/sdk`](https://www.npmjs.com/package/@modelcontextprotocol/sdk) package and a Node.js-compatible runtime. [Bun](https://bun.sh), [Node](https://nodejs.org), and [Deno](https://deno.com) all work. The pre-built plugins in the research preview use Bun, but your channel doesn't have to.

Your server needs to:

1. Declare the `claude/channel` capability so Claude Code registers a notification listener
2. Emit `notifications/claude/channel` events when something happens
3. Connect over [stdio transport](https://modelcontextprotocol.io/docs/concepts/transports#standard-io)

The [Server options](#server-options) and [Notification format](#notification-format) sections cover each of these in detail. See [Example: build a webhook receiver](#example-build-a-webhook-receiver) for a full walkthrough.

During the research preview, custom channels aren't on the [approved allowlist](/docs/en/channels#supported-channels). Use `--dangerously-load-development-channels` to test locally. See [Test during the research preview](#test-during-the-research-preview) for details.

## Example: build a webhook receiver

This walkthrough builds a single-file server that listens for HTTP requests and forwards them into your Claude Code session. By the end, anything that can send an HTTP POST, like a CI pipeline, a monitoring alert, or a `curl` command, can push events to Claude.

This example uses [Bun](https://bun.sh) as the runtime for its built-in HTTP server and TypeScript support. You can use [Node](https://nodejs.org) or [Deno](https://deno.com) instead; the only requirement is the [MCP SDK](https://www.npmjs.com/package/@modelcontextprotocol/sdk).

<Steps>
  <Step title="Create the project">
    The permission relay examples later on this page import `zod` directly, so it installs alongside the MCP SDK. Create a new directory and install both:

    ```bash theme={null}
    mkdir webhook-channel && cd webhook-channel
    bun add @modelcontextprotocol/sdk zod
    ```
  </Step>

  <Step title="Write the channel server">
    Create a file called `webhook.ts`. This is your entire channel server: it connects to Claude Code over stdio, and it listens for HTTP POSTs on port 8788. When a request arrives, it pushes the body to Claude as a channel event.

    ```ts title="webhook.ts" theme={null}
    #!/usr/bin/env bun
    import { Server } from '@modelcontextprotocol/sdk/server/index.js'
    import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'

    // Create the MCP server and declare it as a channel
    const mcp = new Server(
      { name: 'webhook', version: '0.0.1' },
      {
        // this key is what makes it a channel — Claude Code registers a listener for it
        capabilities: { experimental: { 'claude/channel': {} } },
        // added to Claude's system prompt so it knows how to handle these events
        instructions: 'Events from the webhook channel arrive as <channel source="webhook" ...>. They are one-way: read them and act, no reply expected.',
      },
    )

    // Connect to Claude Code over stdio (Claude Code spawns this process)
    await mcp.connect(new StdioServerTransport())

    // Start an HTTP server that forwards every POST to Claude
    Bun.serve({
      port: 8788,  // any open port works
      // localhost-only: nothing outside this machine can POST
      hostname: '127.0.0.1',
      async fetch(req) {
        const body = await req.text()
        await mcp.notification({
          method: 'notifications/claude/channel',
          params: {
            content: body,  // becomes the body of the <channel> tag
            // each key becomes a tag attribute, e.g. <channel path="/" method="POST">
            meta: { path: new URL(req.url).pathname, method: req.method },
          },
        })
        return new Response('ok')
      },
    })
    ```

    The file does three things in order:

    * **Server configuration**: creates the MCP server with `claude/channel` in its capabilities, which is what tells Claude Code this is a channel. The [`instructions`](#server-options) string goes into Claude's system prompt: tell Claude what events to expect, whether to reply, and how to route replies if it should.
    * **Stdio connection**: connects to Claude Code over stdin/stdout. This is standard for any [MCP server](https://modelcontextprotocol.io/docs/concepts/transports#standard-io).
    * **HTTP listener**: starts a local web server on port 8788. Every POST body gets forwarded to Claude as a channel event via `mcp.notification()`. The `content` becomes the event body, and each `meta` entry becomes an attribute on the `<channel>` tag. The listener needs access to the `mcp` instance, so it runs in the same process. You could split it into separate modules for a larger project.
  </Step>

  <Step title="Register your server with Claude Code">
    Add the server to your MCP config so Claude Code knows how to start it. For a project-level `.mcp.json` in the same directory, use a relative path. For user-level config in `~/.claude.json`, use the full absolute path so the server can be found from any project:

    ```json title=".mcp.json" theme={null}
    {
      "mcpServers": {
        "webhook": { "command": "bun", "args": ["./webhook.ts"] }
      }
    }
    ```

    Claude Code reads your MCP config at startup and spawns each server as a subprocess.
  </Step>

  <Step title="Test it">
    During the research preview, custom channels aren't on the allowlist, so start Claude Code with the development flag:

    ```bash theme={null}
    claude --dangerously-load-development-channels server:webhook
    ```

    Claude Code first shows a full-screen warning dialog listing the development channels you're loading. Select **I am using this for local development** to continue, or **Exit** to quit.

    The first time you start a session in this project, Claude Code also asks for consent before using the new server from `.mcp.json`. The dialog reports "New MCP server found in this project: webhook". Select **Use this MCP server** to continue.

    After you accept, Claude Code spawns your `webhook.ts` as a subprocess, and the HTTP listener starts automatically on the port you configured, 8788 in this example. You don't need to run the server yourself.

    A dim notice below the startup banner confirms the channel is registered: `Channels (experimental) messages from server:webhook inject directly in this session · restart without --dangerously-load-development-channels to stop`.

    If you see "blocked by org policy," your organization admin needs to [enable channels](/docs/en/channels#enterprise-controls) first.

    In a separate terminal, simulate a webhook by sending an HTTP POST with a message to your server. This example sends a CI failure alert to port 8788 (or whichever port you configured):

    ```bash theme={null}
    curl -X POST localhost:8788 -d "build failed on main: https://ci.example.com/run/1234"
    ```

    The payload arrives in Claude's context as a `<channel>` tag:

    ```text theme={null}
    <channel source="webhook" path="/" method="POST">build failed on main: https://ci.example.com/run/1234</channel>
    ```

    Your terminal renders the event as a one-line summary, `← webhook: build failed on main: https://ci.example.com/run/1234`, rather than the raw tag. You'll then see Claude start responding: reading files, running commands, or whatever the message calls for. This is a one-way channel, so Claude acts in your session but doesn't send anything back through the webhook. To add replies, see [Expose a reply tool](#expose-a-reply-tool).

    If the event doesn't arrive, the diagnosis depends on what `curl` returned:

    * **`curl` succeeds but nothing reaches Claude**: run `/mcp` in your session to check the server's status. "Failed to connect" usually means a dependency or import error in your server file; check the debug log at `~/.claude/debug/<session-id>.txt` for the stderr trace.
    * **`curl` fails with "connection refused"**: the port is either not bound yet or a stale process from an earlier run is holding it. `lsof -i :<port>` shows what's listening; `kill` the stale process before restarting your session.
  </Step>
</Steps>

The [fakechat server](https://github.com/anthropics/claude-plugins-official/tree/main/external_plugins/fakechat) extends this pattern with a web UI, file attachments, and a reply tool for two-way chat.

## Test during the research preview

During the research preview, every channel must be on the [approved allowlist](/docs/en/channels#research-preview) to register. The development flag bypasses the allowlist for specific entries after a confirmation prompt. This example shows both entry types:

```bash theme={null}
# Testing a plugin you're developing
claude --dangerously-load-development-channels plugin:yourplugin@yourmarketplace

# Testing a bare .mcp.json server (no plugin wrapper yet)
claude --dangerously-load-development-channels server:webhook
```

The bypass is per-entry. Combining this flag with `--channels` doesn't extend the bypass to the `--channels` entries. During the research preview, the approved allowlist is Anthropic-curated, so your channel stays on the development flag while you build and test.

<Note>
  This flag skips the allowlist only. The `channelsEnabled` organization policy still applies. Don't use it to run channels from untrusted sources.
</Note>

## Server options

A channel sets these options in the [`Server`](https://modelcontextprotocol.io/docs/learn/server-concepts) constructor. The `instructions` and `capabilities.tools` fields are [standard MCP](https://modelcontextprotocol.io/docs/learn/server-concepts); `capabilities.experimental['claude/channel']` and `capabilities.experimental['claude/channel/permission']` are the channel-specific additions:

| Field                                                    | Type     | Description                                                                                                                                                                                                                                                             |
| :------------------------------------------------------- | :------- | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `capabilities.experimental['claude/channel']`            | `object` | Required. Always `{}`. Presence registers the notification listener.                                                                                                                                                                                                    |
| `capabilities.experimental['claude/channel/permission']` | `object` | Optional. Always `{}`. Declares that this channel can receive permission relay requests. When declared, Claude Code forwards tool approval prompts to your channel so you can approve or deny them remotely. See [Relay permission prompts](#relay-permission-prompts). |
| `capabilities.tools`                                     | `object` | Two-way only. Always `{}`. Standard MCP tool capability. See [Expose a reply tool](#expose-a-reply-tool).                                                                                                                                                               |
| `instructions`                                           | `string` | Recommended. Added to Claude's system prompt. Tell Claude what events to expect, what the `<channel>` tag attributes mean, whether to reply, and if so which tool to use and which attribute to pass back (like `chat_id`).                                             |

To create a one-way channel, omit `capabilities.tools`. This example shows a two-way setup with the channel capability, tools, and instructions set:

```ts theme={null}
import { Server } from '@modelcontextprotocol/sdk/server/index.js'

const mcp = new Server(
  { name: 'your-channel', version: '0.0.1' },
  {
    capabilities: {
      experimental: { 'claude/channel': {} },  // registers the channel listener
      tools: {},  // omit for one-way channels
    },
    // added to Claude's system prompt so it knows how to handle your events
    instructions: 'Messages arrive as <channel source="your-channel" ...>. Reply with the reply tool.',
  },
)
```

## Notification format

Your server emits `notifications/claude/channel` with two params:

| Field     | Type                     | Description                                                                                                                                                                                                                                                           |
| :-------- | :----------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `content` | `string`                 | The event body. Delivered as the body of the `<channel>` tag.                                                                                                                                                                                                         |
| `meta`    | `Record<string, string>` | Optional. Each entry becomes an attribute on the `<channel>` tag for routing context like chat ID, sender name, or alert severity. Keys must be identifiers: letters, digits, and underscores only. Keys containing hyphens or other characters are silently dropped. |

Your server pushes events by calling `mcp.notification()` on the `Server` instance. This example pushes a CI failure alert with two meta keys:

```ts theme={null}
await mcp.notification({
  method: 'notifications/claude/channel',
  params: {
    content: 'build failed on main: https://ci.example.com/run/1234',
    meta: { severity: 'high', run_id: '1234' },
  },
})
```

The event arrives in Claude's context wrapped in a `<channel>` tag. The `source` attribute is set automatically from your server's configured name:

```text theme={null}
<channel source="your-channel" severity="high" run_id="1234">
build failed on main: https://ci.example.com/run/1234
</channel>
```

Claude Code doesn't acknowledge notifications. The `await` on `mcp.notification()` resolves when the message is written to the transport, not when Claude has processed it. If the session hasn't loaded your server as a channel, or the organization policy blocks it, Claude Code drops the events silently and returns no error to your server.

If you need delivery confirmation, track event state in your server and expose a [reply tool](#expose-a-reply-tool) that Claude can call to report status back.

Events queue into the session and are processed in order. If several notifications arrive while Claude is busy, they're delivered together on the next turn and Claude handles them as a group. To process independent event streams concurrently, run separate sessions.

## Expose a reply tool

If your channel is two-way, like a chat bridge rather than an alert forwarder, expose a standard [MCP tool](https://modelcontextprotocol.io/docs/concepts/tools) that Claude can call to send messages back. Nothing about the tool registration is channel-specific. A reply tool has three components:

1. A `tools: {}` entry in your `Server` constructor capabilities so Claude Code discovers the tool
2. Tool handlers that define the tool's schema and implement the send logic
3. An `instructions` string in your `Server` constructor that tells Claude when and how to call the tool

To add these to the [webhook receiver above](#example-build-a-webhook-receiver):

<Steps>
  <Step title="Enable tool discovery">
    In your `Server` constructor in `webhook.ts`, add `tools: {}` to the capabilities so Claude Code knows your server offers tools:

    ```ts theme={null}
    capabilities: {
      experimental: { 'claude/channel': {} },
      tools: {},  // enables tool discovery
    },
    ```
  </Step>

  <Step title="Register the reply tool">
    Add the following to `webhook.ts`. The `import` goes at the top of the file with your other imports; the two handlers go between the `Server` constructor and `mcp.connect()`. This registers a `reply` tool that Claude can call with a `chat_id` and `text`:

    ```ts theme={null}
    // Add this import at the top of webhook.ts
    import { ListToolsRequestSchema, CallToolRequestSchema } from '@modelcontextprotocol/sdk/types.js'

    // Claude queries this at startup to discover what tools your server offers
    mcp.setRequestHandler(ListToolsRequestSchema, async () => ({
      tools: [{
        name: 'reply',
        description: 'Send a message back over this channel',
        // inputSchema tells Claude what arguments to pass
        inputSchema: {
          type: 'object',
          properties: {
            chat_id: { type: 'string', description: 'The conversation to reply in' },
            text: { type: 'string', description: 'The message to send' },
          },
          required: ['chat_id', 'text'],
        },
      }],
    }))

    // Claude calls this when it wants to invoke a tool
    mcp.setRequestHandler(CallToolRequestSchema, async req => {
      if (req.params.name === 'reply') {

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