Monitor Empty n8n Workflows & Send Slack Alerts via API

Catch “successful but empty” n8n workflows—and get Slack alerts fast

This n8n automation runs hourly to monitor your selected workflows via the n8n API, records health checks in an n8n Data Table, and posts Slack alerts when a workflow succeeds but produces zero items—or when it becomes stale.

What this workflow does

• Runs every hour on a schedule to perform a fresh health sweep.
• Loads watchdog thresholds (including grace period, alert cooldown, escalation, and your n8n instance URL) and pulls the list of watched workflow IDs from the workflow_output_watchdog Data Table.
• Checks each watched workflow by calling the n8n API to fetch the most recent successful execution and then retrieving the execution’s run data.
• Detects “successful but empty” runs by counting how many items the final executed node produced—and also totaling items across the run.
• Classifies health status as HEALTHY, EMPTY, STALE, DARK, or UNREADABLE, based on item counts and how long it’s been since the last successful success.
• Upserts results back to the Data Table, updating verdicts, counters, timestamps, and the last execution ID.
• Sends formatted Slack messages only when alert rules are met.
• Posts an additional Slack message if any watched workflows were not checked during the sweep.

Use cases

• Monitor reporting/ETL workflows to ensure they don’t “run successfully” but output zero items.
• Detect stalled automations by alerting when a workflow becomes STALE (no recent success).
• Catch configuration or API issues when a workflow is UNREADABLE or appears DARK.

Technical details

• Integrations: n8n API (to fetch executions and run data), Slack (to send alerts).
• Nodes/logic used: if, n8n, set, code, no op, limit.
• Data storage: n8n Data Table workflow_output_watchdog (tracks workflow_id, label, thresholds, verdict state, timestamps, and last_execution_id).

Result: you get reliable n8n workflow health monitoring with Slack alerts for empty and stale executions—using only what your workflows already produce.