Skip to main content
Kestrel’s built-in integrations cover the most common tools in the cloud operations stack. For everything else — internal APIs, niche SaaS products, or any service with an HTTP API or webhooks — you can build custom action blocks and webhook trigger blocks. Custom blocks are created from the workflow builder sidebar by clicking Create Custom Workflow Block.

​
Custom Action Blocks (HTTP)

A custom HTTP action block lets you call any API endpoint as a workflow step. Define the request template once, then reuse it across workflows with dynamic parameters.

​
Quickest Method: Paste a cURL Command

The fastest way to create a custom action block is to paste a cURL command. Kestrel automatically extracts the method, URL, headers, body, and authentication. Credentials are detected and stored securely.
1

Open the block builder

In the workflow builder sidebar, click Create Custom Workflow Block and select Action Block.
2

Paste a cURL command

Paste a cURL command from the API you want to call. Kestrel’s AI agent automatically extracts:
  • HTTP method and URL
  • Headers (including authentication headers)
  • Request body
  • Authentication type (API key, bearer token, or basic auth)
  • Response mapping suggestions
  • Parameter definitions for dynamic values
3

Review and adjust

Review the auto-detected configuration. The AI agent chooses the right authentication method and suggests which values should be parameterized. Adjust names, descriptions, and defaults as needed.
4

Save

Click Create to save the custom action block. It appears in the workflow sidebar under your custom integration group and can be used in any workflow.
You can also click Skip — build from scratch to manually configure every field if you prefer full control.

​
Manual Configuration (Build from Scratch)

If you prefer to configure everything manually: Request Configuration:
FieldDescriptionExample
MethodHTTP methodPOST, GET, PUT, PATCH, DELETE
URLEndpoint URL (supports template variables)https://api.example.com/v1/alerts/{{trigger.alert_id}}
HeadersRequest headers as key-value pairsContent-Type: application/json
BodyRequest body (JSON){"message": "{{rca_result.root_cause}}"}
Authentication:
Send an API key as a header.
  • Header Name: The header to set (e.g., X-API-Key)
  • API Key: The key value (stored encrypted)
Credentials are stored encrypted and never exposed in workflow logs or execution history.
Response Mapping: Define output variables by mapping JSON paths from the API response:
Output Variable NameJSON PathDescription
status$.statusResponse status field
result_id$.data.idID from nested response
message$.messageResponse message
Mapped variables become available as {{step_outputs.<action-id>.<variable>}} in downstream steps. Parameters: Define named parameters that appear as configurable fields when the custom action is added to a workflow canvas.
FieldTypeDescription
NamestringParameter identifier used in URL/body templates
LabelstringDisplay label in the UI
DescriptionstringHelp text shown to the user
DefaultanyDefault value (optional)

​
Custom Trigger Blocks (Webhooks)

A custom webhook trigger lets you start a workflow from any external service that can send HTTP POST requests.

​
Quickest Method: Paste an Example Payload

The fastest way to create a webhook trigger is to paste a sample JSON payload from the external service. Kestrel automatically detects the event type field and extracts useful fields for your workflow.
1

Open the block builder

In the workflow builder sidebar, click Create Custom Workflow Block and select Trigger Block.
2

Paste an example webhook payload

Paste a sample JSON payload from the external service. Kestrel automatically:
  • Detects the event type field (e.g., type, event, event_type)
  • Extracts useful fields as template variables
  • Generates a payload mapping with sensible variable names
  • Suggests a name and description for the trigger block
3

Review field mapping

Review the auto-detected field mapping. Rename variables, adjust which fields are extracted, and configure event type filtering if needed.
4

Configure security (optional)

Enable HMAC signature verification and enter the signing secret from the external service.
5

Save and copy webhook URL

Click Create to save the trigger block. Copy the generated webhook URL and configure it in the external service as the webhook destination.
You can also click Skip — build from scratch to manually define every field mapping and configuration option.

​
Webhook URL

Each custom webhook trigger gets a unique URL: 
https://platform.usekestrel.ai/api/webhooks/custom/<webhook-path>
Configure this URL in the external service as the webhook destination.

​
HMAC Signature Verification

Enable HMAC verification to ensure webhook payloads are authentic:
  1. Enter the Signing Secret provided by the external service
  2. Specify the Signature Header name (e.g., X-Hub-Signature-256, Stripe-Signature)
Kestrel validates the HMAC signature on every incoming request and rejects payloads that don’t match.
Without HMAC verification, any HTTP client that knows the webhook URL can trigger the workflow. Enable verification for production workflows.

​
Event Type Filtering

If the external service sends different event types to the same webhook, configure the trigger to only fire for specific event types. The event type path is auto-detected when you paste a sample payload, or you can configure it manually.

​
Payload Field Mapping

When you paste an example payload, Kestrel parses the JSON and generates a field map: 
{
  "type": "email.delivered",
  "data": {
    "email_id": "em_abc123",
    "to": "user@example.com",
    "subject": "Your invoice"
  }
}
Auto-detected variables become available as {{signal.<field_name>}} in the workflow:
VariableMapped FromDescription
{{signal.event_type}}typeThe webhook event type
{{signal.email_id}}data.email_idExtracted email ID
{{signal.to}}data.toRecipient email address
{{signal.subject}}data.subjectEmail subject line

​
Examples

​
Resend Email Events

Workflow Agent prompt: “When a Resend email bounces, send a notification to #email-ops in Slack with the bounce details and create a Jira ticket for the email team to investigate.” Trigger: Custom webhook trigger with Resend’s email.bounced event type. Example payload: 
{
  "type": "email.bounced",
  "data": {
    "email_id": "em_abc123",
    "to": "user@example.com",
    "subject": "Your invoice",
    "bounce_type": "hard"
  }
}
Workflow: On bounce → Slack notification to #email-ops with bounce details → Jira ticket for investigation.

​
Stripe Payment Webhooks

Workflow Agent prompt: “When a Stripe payment fails, investigate the customer’s recent activity, send an alert to #payments in Slack with the failure details, and create a PagerDuty alert if the amount is over $1000.” Trigger: Custom webhook filtered to payment_intent.payment_failed. HMAC enabled with Stripe’s webhook signing secret, header Stripe-Signature. Workflow: On failed payment → Kestrel Investigation with customer context → Slack alert to #payments → conditional PagerDuty alert.

​
Internal Service Events

Workflow Agent prompt: “When our deployment service sends a deploy event, generate the K8s manifests based on the deployment spec, create a GitOps PR in acme/k8s-manifests, and trigger an ArgoCD sync after the PR is merged.” Trigger: Custom webhook with your application’s deployment event schema. Workflow: On deployment event → Generate K8s manifests → Create GitOps PR → Wait for PR merge → ArgoCD sync.

​
Next Steps