Slack Channel Welcome Message: A Tested Bot and the Free-Plan Catch

To post a welcome message when someone joins a Slack channel, you need a workflow or a small bot, because Slack has no channel setting for it. On a paid plan, Workflow Builder can start a workflow when someone joins a channel. On a Free plan it cannot, and a bot that listens for the member_joined_channel event works on any plan. On 9 November 2026 we ran such a bot in a Free test workspace: a Bolt for Python app over Socket Mode that sends the new member a private note and posts a public welcome. The welcome landed 1.2 s after the join.

In the screenshot, each join is followed by the public welcome, and the new member also sees a note marked "Only visible to you". That note is an ephemeral message. Nobody else sees it, and it is gone after a reload.

Workflow Builder on the Free plan

Workflow Builder used to be the no-code answer. In our Free workspace, the Workflows page said "Free teams do not have access to use workflows" and the New Workflow button carried a Pro label:

On a paid plan, start a new workflow from the "When someone joins a channel" event and add a "Send a message" step. We could not test that path on Free. The bot below has no plan limit.

The bot

Create an app, turn on Socket Mode, and give it these bot scopes: channels:read (for the event in public channels), groups:read (private channels), chat:write. Subscribe to the bot event member_joined_channel, install the app, and invite the bot to each channel that should greet people. The Socket Mode guide shows where the xapp- token comes from, and the bot token guide covers the xoxb- one.

import json, logging, os, time
logging.basicConfig(level=logging.INFO)
from slack_bolt import App
from slack_bolt.adapter.socket_mode import SocketModeHandler

app = App(token=os.environ["SLACK_BOT_TOKEN"])
WELCOME_CHANNELS = {os.environ["WELCOME_CHANNEL"]}
BOT_USER = app.client.auth_test()["user_id"]

@app.event("member_joined_channel")
def welcome(event, client, logger):
    print("EVENT", json.dumps(event), flush=True)
    if event["channel"] not in WELCOME_CHANNELS or event["user"] == BOT_USER:
        return
    t0 = time.time()
    client.chat_postEphemeral(
        channel=event["channel"], user=event["user"],
        text=f"Welcome <@{event['user']}>! Pinned: the team handbook and the on-call rota.",
    )
    t1 = time.time()
    client.chat_postMessage(
        channel=event["channel"],
        text=f":wave: Please welcome <@{event['user']}> to <#{event['channel']}>!",
    )
    print("POSTED ephemeral %.2f s, message %.2f s" % (t1 - t0, time.time() - t1), flush=True)

if __name__ == "__main__":
    SocketModeHandler(app, os.environ["SLACK_APP_TOKEN"]).start()

Run it with the two tokens and the channel ID:

pip install slack_bolt
SLACK_BOT_TOKEN=xoxb-... SLACK_APP_TOKEN=xapp-... WELCOME_CHANNEL=C0123456789 python welcome.py

Socket Mode means the app opens the connection to Slack, so it runs on a laptop or a small server with no public URL. To serve it over HTTP instead, see running a Slack bot behind a tunnel.

What the event looks like

When our test member left the channel and joined again, Bolt got:

{"type": "member_joined_channel", "user": "U0CDVBA6TMZ", "channel": "C0CGUSWDK08", "channel_type": "C", "team": "T0B7JBCDKC1", "event_ts": "1794204061.000700"}

When the bot invited the member instead, the event also had "inviter": "U0CG27WHFC1". Use that field if you want a different message for people who were added by someone else.

Our log after three joins:

POSTED ephemeral 0.32 s, message 0.33 s
POSTED ephemeral 0.32 s, message 0.33 s
POSTED ephemeral 0.32 s, message 0.33 s

Each Web API call took about a third of a second, and the public welcome appeared 1.24 s after the join's event_ts.

Two details that tripped us

The bot's own join fires the same event. When you invite the bot to a channel, member_joined_channel arrives with the bot's user ID, so the code compares event["user"] with the bot's ID from auth.test and skips it. Without that check, the bot welcomes itself.

Bolt also logged an "Unhandled request" warning for every join, with a 404 result. Our app was subscribed to message.channels too, and every join creates a channel_join message, which no listener handled. Either drop that subscription or add an empty @app.event("message") listener. The welcome itself worked either way.

Public welcome, private note or DM

A public welcome on every join gets noisy in big channels. For those, the ephemeral note or a DM is kinder, and our ephemeral message guide covers its limits. If you also want to hide Slack's own "has joined the channel" lines, see how to turn off join messages.

FAQ

Can I welcome people to the whole workspace instead of one channel?

Yes. Listen for team_join (scope users:read) and send a DM. People join a workspace once, so that event fires once per person.

Does this work in private channels?

Yes, with the groups:read scope and the bot invited to the private channel. We tested a public channel only.

Can I post the welcome in a thread?

Pass thread_ts of a pinned intro message to chat.postMessage. The welcomes then stack under one message instead of filling the channel.