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Socket Mode

Slack Socket Mode


$ npm install @slack/socket-mode

Initialize the client

This package is designed to support Socket Mode, which allows your app to receive events from Slack over a WebSocket connection.

The package exports a SocketModeClient class. Your app will create an instance of the class for each workspace it communicates with. Creating an instance requires an app-level token from Slack. Apps connect to the Socket Mode API using an app-level token, which starts with xapp.

Note: Socket Mode requires the connections:write scope. Navigate to your app configuration and go to the OAuth and Permissions section to add the scope.

const { SocketModeClient } = require('@slack/socket-mode');

// Read a token from the environment variables
const appToken = process.env.SLACK_APP_TOKEN;

// Initialize
const client = new SocketModeClient({appToken});

Connect to Slack

After your client establishes a connection, your app can send data to and receive data from Slack. Connecting is as easy as calling the .start() method.

const { SocketModeClient } = require('@slack/socket-mode');
const appToken = process.env.SLACK_APP_TOKEN;

const socketModeClient = new SocketModeClient(appToken);

(async () => {
  // Connect to Slack
  await socketModeClient.start();

Listen for an event

Bolt apps register listener functions, which are triggered when a specific event type is received by the client.

If you’ve used Node’s EventEmitter pattern before, then you’re already familiar with how this works, since the client is an EventEmitter.

The event argument passed to the listener is an object. Its content corresponds to the type of event it’s registered for.

const { SocketModeClient } = require('@slack/socket-mode');
const appToken = process.env.SLACK_APP_TOKEN;

const socketModeClient = new SocketModeClient(appToken);

// Attach listeners to events by type. See:
socketModeClient.on('message', (event) => {

(async () => {
  await socketModeClient.start();

Send a message

To respond to events and send messages back into Slack, we recommend using the @slack/web-api package with a bot token.

const { SocketModeClient } = require('@slack/socket-mode');
const { WebClient } = require('@slack/web-api');

const socketModeClient = new SocketModeClient(process.env.SLACK_APP_TOKEN);
const webClient = new WebClient(process.env.BOT_TOKEN);

// Attach listeners to events by type. See:
socketModeClient.on('member_joined_channel', async ({event, body, ack}) => {
    try {
      // send acknowledgement back to slack over the socketMode websocket connection
      // this is so slack knows you have received the event and are processing it
      await ack();
          blocks: [
            type: 'section',
            text: {
              type: 'mrkdwn',
              text: `Welcome to the channel, <@${event.user}>. We're here to help. Let us know if you have an issue.`,
            accessory: {
              type: 'button',
              text: {
                type: 'plain_text',
                text: 'Get Help',
              value: 'get_help',
    } catch (error) {
      console.log('An error occurred', error);

Lifecycle events

The client’s connection to Slack has a lifecycle. This means the client can be seen as a state machine which transitions through a few states as it connects, disconnects, reconnects, and synchronizes with Slack. The client emits an event for each state it transitions to throughout its lifecycle. If your app simply needs to know whether the client is connected or not, the .connected boolean property can be checked.

In the table below, the client’s states are listed, which are also the names of the events you can use to observe the transition to that state. The table also includes descriptions for the states and arguments that a listener would receive.

Event Name Arguments Description
connecting   The client is in the process of connecting to the platform.
authenticated (connectData) - the response from The client has authenticated with the platform. This is a sub-state of connecting.
connected   The client is connected to the platform and incoming events will start being emitted.
ready   The client is ready to send outgoing messages. This is a sub-state of connected
disconnecting   The client is no longer connected to the platform and cleaning up its resources. It will soon transition to disconnected.
reconnecting   The client is no longer connected to the platform and cleaning up its resources. It will soon transition to connecting.
disconnected (error) The client is not connected to the platform. This is a steady state - no attempt to connect is occurring. The error argument will be undefined when the client initiated the disconnect (normal).

The client also emits events that are part of its lifecycle, but aren’t states. Instead, they represent specific moments that might be helpful to your app. The following table lists these events, their description, and includes the arguments that a listener would receive.

Event Name Arguments Description
error (error) An error has occurred. See error handling for details.
slack_event (eventType, event) An incoming Slack event has been received.
unable_to_socket_mode_start (error) A problem occurred while connecting, a reconnect may or may not occur.


The SocketModeClient will log interesting information to the console by default. You can use the logLevel to decide how much or what kind of information should be output. There are a few possible log levels, which you can find in the LogLevel export. By default, the value is set to LogLevel.INFO. While you’re in development, it’s sometimes helpful to set this to the most verbose: LogLevel.DEBUG.

// Import LogLevel from the package
const { SocketModeClient, LogLevel } = require('@slack/socket-mode');
const appToken = process.env.SLACK_APP_TOKEN;

// Log level is one of the options you can set in the constructor
const socketModeClient = new SocketModeClient({
  logLevel: LogLevel.DEBUG,

(async () => {
  await socketModeClient.start();

All the log levels, in order of most to least information are: DEBUG, INFO, WARN, and ERROR.

Sending log output somewhere besides the console

You can also choose to have logs sent to a custom logger using the logger option. A custom logger needs to implement specific methods (known as the Logger interface):

Method Parameters Return type
setLevel() level: LogLevel void
setName() name: string void
debug() ...msgs: any[] void
info() ...msgs: any[] void
warn() ...msgs: any[] void
error() ...msgs: any[] void

A very simple custom logger might ignore the name and level, and write all messages to a file.

const { createWriteStream } = require('fs');
const logWritable = createWriteStream('/var/my_log_file'); // Not shown: close this stream

const socketModeClient = new SocketModeClient(appToken, {
  // Creating a logger as a literal object. It's more likely that you'd create a class.
  logger: {
    debug(...msgs): { logWritable.write('debug: ' + JSON.stringify(msgs)); },
    info(...msgs): { logWritable.write('info: ' + JSON.stringify(msgs)); },
    warn(...msgs): { logWritable.write('warn: ' + JSON.stringify(msgs)); },
    error(...msgs): { logWritable.write('error: ' + JSON.stringify(msgs)); },
    setLevel(): { },
    setName(): { },

(async () => {
  await socketModeClient.start();


This package supports Node v12 LTS and higher. It’s highly recommended to use the latest LTS version of node, and the documentation is written using syntax and features from that version.

Getting Help

If you get stuck, we’re here to help. The following are the best ways to get assistance working through your issue:

  • Issue Tracker for questions, feature requests, bug reports and general discussion related to these packages. Try searching before you create a new issue.