Slack

Creating a Slack App

To send messages to Slack channels or users, you first need to create a Slack App and configure an Incoming Webhook.

Create a new app

Go to the Slack API Apps page and click Create New App → From scratch.

Name and workspace

Choose a name for the app and select the Slack workspace where it will be installed.

Enable Incoming Webhooks

In the app settings, navigate to Incoming Webhooks and enable them.

Add a webhook to a channel

Click Add New Webhook to Workspace and choose the channel you want the app to post to.

Copy the webhook URL

Copy the Webhook URL — you’ll use this to send messages.

For more information, refer to the official Slack Webhook documentation.

Caution

Keep the webhook URL secret — it authenticates requests to your workspace.

Example Webhook URL

https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX

Notification Implementation

Store the webhook URL as SLACK_WEBHOOK_URL in the secrets store; it reaches the build as an environment variable. Then post messages with a simple HTTP POST request. The webhook always posts to the channel it was created for.

import os

import polars as pl
import requests

SLACK_WEBHOOK_URL = os.environ["SLACK_WEBHOOK_URL"]


def send_slack_message(message):
    response = requests.post(SLACK_WEBHOOK_URL, json={"text": message}, timeout=10)
    # Slack answers with the plain text "ok", or an error status with the reason
    response.raise_for_status()


def transform():
    send_slack_message("⚠️ *New Alert!*")
    return pl.LazyFrame({"sent": [True]})

Example Message Formatting

Formatting and examples

Slack supports basic formatting using Markdown-like syntax:

• *bold* → bold
• _italic_ → italic
• `code` → code
• <https://example.com|Custom Link> → Custom Link

You can also include emojis and attachments for richer notifications.