Human in the Loop

The Human in the Loop block pauses workflow execution and waits for human intervention before continuing. Use it to add approval gates, collect feedback, or gather additional input at critical decision points.

When execution reaches this block, the workflow pauses indefinitely until a human provides input through the approval portal, API, or webhook.

Configuration Options

Display Data

Defines what data is displayed to the approver. This is the context shown in the approval portal to help them make an informed decision.

Use the visual builder or JSON editor to structure the data. Reference workflow variables using <blockName.output> syntax.

{
  "customerName": "<agent1.content.name>",
  "proposedAction": "<router1.selectedPath>",
  "confidenceScore": "<evaluator1.score>",
  "generatedEmail": "<agent2.content>"
}

Notification

Configures how approvers are alerted when approval is needed. Supported channels include:

Slack - Messages to channels or DMs
Gmail - Email with approval link
Microsoft Teams - Team channel notifications
SMS - Text alerts via Twilio
Webhooks - Custom notification systems

Include the approval URL (<blockId.url>) in your notification messages so approvers can access the portal.

Resume Form

Defines the fields approvers fill in when responding. This data becomes available to downstream blocks after the workflow resumes.

{
  "approved": {
    "type": "boolean",
    "description": "Approve or reject this request"
  },
  "comments": {
    "type": "string",
    "description": "Optional feedback or explanation"
  }
}

Access resume data in downstream blocks using <blockId.fieldName>.

Approval Methods

Approval Portal

Every block generates a unique portal URL (<blockId.url>) with a visual interface showing all paused output data and form fields for resume input. Mobile-responsive and secure.

Share this URL in notifications for approvers to review and respond.

REST API

Programmatically resume workflows using the resume endpoint. The contextId is available from the block's resumeEndpoint output or from the _resume object in the paused execution response.

POST /api/resume/{workflowId}/{executionId}/{contextId}
Content-Type: application/json
X-API-Key: your-api-key

{
  "input": {
    "approved": true,
    "comments": "Looks good to proceed"
  }
}

The resume endpoint automatically respects the execution mode used in the original execute call:

Sync mode (default) — The response waits for the remaining workflow to complete and returns the full result:

{
  "success": true,
  "status": "completed",
  "executionId": "<resumeExecutionId>",
  "output": { ... },
  "metadata": { "duration": 1234, "startTime": "...", "endTime": "..." }
}

If the resumed workflow hits another HITL block, the response returns "status": "paused" with new _resume URLs in the output.

Stream mode (stream: true on the original execute call) — The resume response streams SSE events with selectedOutputs chunks, just like the initial execution.
Async mode (X-Execution-Mode: async on the original execute call) — The resume dispatches execution to a background worker and returns immediately with 202:

{
  "status": "started",
  "executionId": "<resumeExecutionId>",
  "message": "Resume execution started asynchronously."
}

Polling execution status

To check on a paused execution or poll for completion after an async resume:

GET /api/resume/{workflowId}/{executionId}
X-API-Key: your-api-key

Returns the full paused execution detail with all pause points, their statuses, and resume links. Returns 404 when the execution has completed and is no longer paused.

Webhook

Add a webhook tool to the Notification section to send approval requests to external systems. Integrate with ticketing systems like Jira or ServiceNow.

API Execute Behavior

When triggering a workflow via the execute API (POST /api/workflows/{id}/execute), HITL blocks cause the execution to pause and return the _resume data in the response:

The response includes the full pause data with resume URLs:

{
  "success": true,
  "executionId": "<executionId>",
  "output": {
    "data": {
      "operation": "human",
      "_resume": {
        "apiUrl": "/api/resume/{workflowId}/{executionId}/{contextId}",
        "uiUrl": "/resume/{workflowId}/{executionId}",
        "contextId": "<contextId>",
        "executionId": "<executionId>",
        "workflowId": "<workflowId>"
      }
    }
  }
}

Blocks before the HITL stream their selectedOutputs normally. When execution pauses, the final SSE event includes status: "paused" and the _resume data:

data: {"blockId":"agent1","chunk":"streamed content..."}
data: {"event":"final","data":{"success":true,"output":{...,"_resume":{...}},"status":"paused"}}
data: "[DONE]"

On resume, blocks after the HITL stream their selectedOutputs the same way.

HITL blocks are automatically excluded from the selectedOutputs dropdown since their data is always included in the pause response.

Returns 202 immediately. Use the polling endpoint to check when the execution pauses.

Common Use Cases

Content Approval - Review AI-generated content before publishing

Agent → Human in the Loop → API (Publish)

Multi-Stage Approvals - Chain multiple approval steps for high-stakes decisions

Agent → Human in the Loop (Manager) → Human in the Loop (Director) → Execute

Data Validation - Verify extracted data before processing

Agent (Extract) → Human in the Loop (Validate) → Function (Process)

Quality Control - Review AI outputs before sending to customers

Agent (Generate) → Human in the Loop (QA) → Gmail (Send)

Block Outputs

url - Unique URL for the approval portal resumeEndpoint - Resume API endpoint URL response - Display data shown to the approver (json) submission - Form submission data from the approver (json) submittedAt - ISO timestamp when the workflow was resumed <fieldName> - All fields defined in Resume Form become available at the top level after the workflow resumes

Access using <blockId.fieldName>.

Example

Paused Output:

{
  "title": "<agent1.content.title>",
  "body": "<agent1.content.body>",
  "qualityScore": "<evaluator1.score>"
}

Resume Input:

{
  "approved": { "type": "boolean" },
  "feedback": { "type": "string" }
}

Downstream Usage:

// Condition block
<approval1.approved> === true

The example below shows an approval portal as seen by an approver after the workflow is paused. Approvers can review the data and provide inputs as a part of the workflow resumption. The approval portal can be accessed directly via the unique URL, <blockId.url>.

Condition - Branch based on approval decisions
Variables - Store approval history and metadata
Response - Return workflow results to API callers

Common Questions

The workflow pauses indefinitely until a human provides input through the approval portal, the REST API, or a webhook. There is no automatic timeout — it will wait until someone responds.

You can configure notifications through Slack, Gmail, Microsoft Teams, SMS (via Twilio), or custom webhooks. Include the approval URL in your notification message so approvers can access the portal directly.

Use the syntax <blockId.fieldName> to reference specific fields from the resume form. For example, if your block name is 'approval1' and the form has an 'approved' field, use <approval1.approved>.

Yes. You can place multiple Human in the Loop blocks in sequence to create multi-stage approval workflows. Each block pauses independently and can have its own notification configuration and resume form fields.

Yes. Each block exposes a resume API endpoint that you can call with a POST request containing the form data as JSON. This lets you build custom approval UIs or integrate with existing systems like Jira or ServiceNow.

The block outputs include the approval portal URL, the resume API endpoint URL, the display data shown to the approver, the form submission data, the raw resume input, and an ISO timestamp of when the workflow was resumed.

Human in the Loop

Common Questions

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