Slack Webhook Alerter

Use this skill when a Python script needs to post a status or result to Slack and you do not want the full Slack SDK or a bot token - an incoming webhook is enough. It builds a Block Kit message with a colored attachment (green/red by status) and posts it with a stdlib request, retrying on transient failures. It mirrors telegram-alerter so the same run can fan out to both channels.

When to invoke

• User says: "send a slack alert", "notify slack", "post to a slack channel", "mirror my telegram alerts to slack".
• Code in the conversation already pushes a run summary somewhere and should also reach a Slack channel.

When NOT to invoke

• The user wants Telegram, Discord, or email instead - use the matching alerter.
• The user needs interactive Slack features (slash commands, modals, threads, reactions); a one-way incoming webhook cannot do those - reach for a bot token and the Slack API.

Concrete example

User input:

After my nightly job finishes, post a green or red Slack message with the item count and a dashboard link.

Output:

# Copy assets/slack_alert.py into your project, then:
from slack_alert import send_slack

ok = send_slack(
    title="Nightly scrape finished",
    text="Processed 42 items in 18 minutes.",
    status="ok",                                  # ok -> green, error -> red, warn -> yellow
    fields={"Items": "42", "Duration": "18m"},
    link=("Open dashboard", "https://example.com/dash"),
)
if not ok:
    print("Slack delivery failed after retries")

The helper reads SLACK_WEBHOOK_URL from the environment. The webhook URL is itself a secret (it grants posting to that channel), so it is never hardcoded.

Pattern to apply

1. Keep the incoming-webhook URL in SLACK_WEBHOOK_URL only - it is a secret, treat it like a token.
2. Map a status string to an attachment color so green/red is readable at a glance.
3. Build a header + section block for the title and body, and a fields list for key/value pairs.
4. Post the JSON payload with a short timeout and retry transient failures with exponential backoff.
5. Escape or trust the text you pass; Slack renders a limited mrkdwn subset, so keep user content plain.

Reference: assets/slack_alert.py.

Source

Distilled from production use across the author's automation projects. v1.0.0. See also: [[telegram-alerter]], [[http-retry-session]], [[pipeline-orchestrator]].

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