How to Post a Slack Notification from GitHub Actions

Send build results to Slack with the official Slack action or a plain incoming-webhook curl.

Store a Slack webhook URL (or bot token) as a secret, then post with slackapi/slack-github-action. Gate it on if: failure() to alert only on red builds.

Notify Slack on failure

This step runs only when an earlier step failed, posting to the configured webhook.

steps:
  - run: npm test
  - name: Notify Slack on failure
    if: failure()
    uses: slackapi/slack-github-action@v2
    with:
      webhook: ${{ secrets.SLACK_WEBHOOK_URL }}
      webhook-type: incoming-webhook
      payload: |
        text: "Build failed on ${{ github.ref_name }} (${{ github.sha }})"

Gotchas

• Without if: failure() (or if: always()), the notify step is skipped when a prior step fails.
• Store the webhook URL as a repo/org secret - it grants posting access to your channel.
• Incoming-webhook payloads use Slack message JSON/blocks; a bot token (chat.postMessage) gives richer formatting.

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