Build Human-in-the-Loop AI Workflows

To add human review to an AI workflow, route the generated content through n8n's Wait node and resume it with a webhook callback. The Wait node pauses execution until a reviewer clicks Approve or Reject -- for example in a Slack message -- and the resume URL carries the decision back into the workflow, so nothing is published until a human approves it.

When should you add a human review step?

For high-stakes outputs -- legal documents, customer-facing communications, financial summaries -- always route AI-generated content through human review before publishing. n8n's Wait node combined with webhook callbacks makes this pattern straightforward.

Real-world example: A workflow generates a weekly customer newsletter using AI, then sends it to a marketing manager via Slack for approval before scheduling it in the email platform.

How do you build a human-in-the-loop approval flow in n8n?

Workflow structure:

[Schedule Trigger] → [Gather Data] → [Generate Newsletter: GPT-4o]
    → [Send to Slack for Review] → [Wait for Approval]
    → [IF: approved] →── yes ──→ [Schedule in Mailchimp]
                      └── no ──→ [Regenerate with Feedback]

Slack message with approval buttons (using Slack Block Kit):

{
  "blocks": [
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "*Weekly Newsletter Draft*\nGenerated: {{ $now.toFormat('dd MMM yyyy') }}"
      }
    },
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "{{ $json.newsletter_preview }}"
      }
    },
    {
      "type": "actions",
      "elements": [
        {
          "type": "button",
          "text": { "type": "plain_text", "text": "Approve" },
          "style": "primary",
          "action_id": "approve",
          "url": "{{ $execution.resumeUrl }}/approve"
        },
        {
          "type": "button",
          "text": { "type": "plain_text", "text": "Reject with Notes" },
          "style": "danger",
          "action_id": "reject",
          "url": "{{ $execution.resumeUrl }}/reject"
        }
      ]
    }
  ]
}

The Wait node pauses execution until the reviewer clicks a button. The resume URL carries the decision:

// Code node after Wait — process the reviewer's decision
const webhookData = $json;

if (webhookData.path === 'approve') {
  return [{ json: { approved: true, newsletter: $('Generate Newsletter').first().json.content } }];
} else {
  return [{ json: { approved: false, feedback: webhookData.body?.notes || 'No specific feedback' } }];
}

How do you keep the workflow from waiting forever?

Tip: Set a Deadline. Configure the Wait node with a Limit Wait Time of 24 hours. If no one reviews in time, route to a fallback (send a reminder, or skip that week's newsletter). Never let a workflow wait indefinitely.

Human-in-the-loop adds a few hours of latency but prevents AI hallucinations from reaching your customers.

Related: Use Manual Trigger During Development Instead of Webhook or Schedule · Flatten Deeply Nested API Responses