Building your first webhook system with Hook0

This tutorial walks through integrating Hook0 into a SaaS platform so your customers can receive webhooks. It uses curl commands throughout, so you can follow along in any language.

What you'll build

A webhook delivery system that:

• Sends events from your SaaS to Hook0
• Lets customers subscribe to specific events
• Handles delivery, retries, and monitoring automatically
• Filters events per tenant using labels

Prerequisites

• Hook0 cloud account or self-hosted instance running
• API token
• Application ID from Hook0
• Basic understanding of REST APIs and webhooks

Set up environment variables

# Set your service token (from dashboard)
export HOOK0_TOKEN="YOUR_TOKEN_HERE"
export HOOK0_API="https://app.hook0.com/api/v1" # Replace by your domain (or http://localhost:8081 locally)

# Set your application ID (shown in dashboard URL or application details)
export APP_ID="YOUR_APPLICATION_ID_HERE"

Save these values:

# Save to .env file for later use
cat > .env <<EOF
HOOK0_TOKEN=$HOOK0_TOKEN
HOOK0_API=$HOOK0_API
APP_ID=$APP_ID
EOF

Architecture overview

Your SaaS sends events to Hook0, which handles delivery, retries, signature verification, and monitoring.

Understanding the API flow

The integration has four steps:

1. Create event types - define what events your SaaS emits
2. Create subscriptions - let customers receive webhooks
3. Send events - push events to Hook0 when actions occur
4. Monitor delivery - track webhook success and failures

Step 1: Define your event types

Hook0 uses a three-part structure for event types: service.resource_type.verb. This gives clear semantics and makes filtering straightforward.

Why define event types first?

Event types act as a contract between your SaaS and customer webhooks. They must be created before you can send events or create subscriptions.

Create a "user created" event type

curl -X POST "$HOOK0_API/event_types" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "service": "user",
    "resource_type": "account",
    "verb": "created"
  }'

Response:

{
  "service_name": "user",
  "resource_type_name": "account",
  "verb_name": "created",
  "event_type_name": "user.account.created"
}

Create an "order completed" event type

curl -X POST "$HOOK0_API/event_types" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "service": "order",
    "resource_type": "purchase",
    "verb": "completed"
  }'

Response:

{
  "service_name":"order",
  "resource_type_name":"purchase",
  "verb_name":"completed",
  "event_type_name":"order.purchase.completed"
}

Step 2: Send events to Hook0

Once event types are defined, your SaaS can start sending events. The /api/v1/event endpoint (singular) accepts individual events.

Why this order?

You must create event types before sending events. Hook0 validates that the event type exists before accepting the event.

Send a user created event

When a user signs up in your SaaS:

curl -X POST "$HOOK0_API/event" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "event_type": "user.account.created",
    "payload": "{\"user_id\": \"usr_789\", \"email\": \"[email protected]\", \"plan\": \"premium\"}",
    "payload_content_type": "application/json",
    "occurred_at": "2024-01-15T10:30:00Z",
    "labels": {
      "tenant_id": "customer_123",
      "environment": "production",
      "region": "us-east-1"
    }
  }'

Response:

{
  "application_id": "{APP_ID}",
  "event_id": "{EVENT_ID}",
  "received_at": "2025-12-12T09:25:28.084734Z"
}

Key points:

• event_id: must be a valid UUID (e.g., 69f69ecf-0d9e-4c92-a6e0-3b2676343940)
• payload: must be a JSON-encoded string, not an object (see warning below)
• labels: required for multi-tenant filtering, must have at least one key-value pair

Payload Format

The payload field must be a JSON-encoded string, not a JSON object:

✅ Correct: "payload": "{\"user_id\": \"usr_789\"}"

❌ Incorrect: "payload": {"user_id": "usr_789"}

This allows Hook0 to forward the exact payload to webhooks without re-serialization.

The tenant_id label ensures events only go to the right customer.

Send an order completed event

When an order is fulfilled:

curl -X POST "$HOOK0_API/event" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "event_type": "order.purchase.completed",
    "payload": "{\"order_id\": \"ord_456\", \"amount\": 299.99, \"items\": 3}",
    "payload_content_type": "application/json",
    "occurred_at": "2024-01-15T11:00:00Z",
    "labels": {
      "tenant_id": "customer_123",
      "environment": "production"
    }
  }'

Response:

{
  "application_id": "{APP_ID}",
  "event_id": "{EVENT_ID}",
  "received_at": "2025-12-12T09:27:27.045191Z"
}

Step 3: Create customer subscriptions

Subscriptions define where and how webhooks get delivered. Each subscription filters events by labels, so customers only receive their own events.

Why labels matter for multi-tenancy

The labels object creates a filter. Only events with matching labels are delivered to that subscription. This is how Hook0 supports multi-tenant SaaS platforms.

Create a subscription for a customer

To follow along, you need a working endpoint URL. Go to play.hook0.com to generate one instantly, then replace the url field in the subscription below with your Play URL.

curl -X POST "$HOOK0_API/subscriptions" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "is_enabled": true,
    "event_types": [
      "user.account.created",
      "order.purchase.completed"
    ],
    "description": "Webhook for Customer ABC Corp",
    "labels": {
      "tenant_id": "customer_123"
    },
    "target": {
      "type": "http",
      "method": "POST",
      "url": "https://customer-abc.com/webhooks/hook0",
      "headers": {
        "X-Customer-Id": "customer_123"
      }
    },
    "metadata": {
      "customer_name": "ABC Corp",
      "created_by": "api",
      "plan": "enterprise"
    }
  }'

Response:

{
  "application_id": "{APP_ID}",
  "subscription_id": "{SUBSCRIPTION_ID}",
  "is_enabled": true,
  "event_types": [
    "user.account.created",
    "order.purchase.completed"
  ],
  "description": "Webhook for Customer ABC Corp",
  "secret": "d48488f1-cddc...",
  "metadata": {
    "customer_name": "ABC Corp",
    "plan": "enterprise",
    "created_by": "api"
  },
  "labels": {
    "tenant_id": "customer_123"
  },
  "target": {
    "type": "http",
    "method": "POST",
    "url": "https://customer-abc.com/webhooks/hook0",
    "headers": {
      "x-customer-id": "customer_123"
    }
  },
  "created_at": "2025-12-12T09:30:13.822397Z",
  "dedicated_workers": []
}

Important: Save the secret - customers need it to verify webhook signatures.

How multi-tenant filtering works

Event labels                 Subscription filter              Result
------------------------     -------------------------        ------------
tenant_id: "customer_123" -> tenant_id = "customer_123"   ->  ✅ Delivered
tenant_id: "customer_456" -> tenant_id = "customer_123"   ->  ❌ Skipped

Step 4: Monitor webhook deliveries

List recent events

See what events have been sent:

curl -X GET "$HOOK0_API/events?application_id=$APP_ID" \
  -H "Authorization: Bearer $HOOK0_TOKEN"

Response:

[
  {
    "event_id": "{EVENT_ID}",
    "event_type_name": "order.purchase.completed",
    "payload_content_type": "application/json",
    "ip": "192.168.97.1",
    "metadata": {},
    "occurred_at": "2024-01-15T11:00:00Z",
    "received_at": "2025-12-12T09:27:27.045191Z",
    "labels": {
      "environment": "production",
      "tenant_id": "customer_123"
    }
  },
  {
    "event_id": "{EVENT_ID}",
    "event_type_name": "user.account.created",
    "payload_content_type": "application/json",
    "ip": "192.168.97.1",
    "metadata": {},
    "occurred_at": "2024-01-15T10:30:00Z",
    "received_at": "2025-12-12T09:25:28.084734Z",
    "labels": {
      "environment": "production",
      "region": "us-east-1",
      "tenant_id": "customer_123"
    }
  },
  {
    "event_id": "{EVENT_ID}",
    "event_type_name": "user.account.created",
    "payload_content_type": "application/json",
    "ip": "192.168.97.1",
    "metadata": {},
    "occurred_at": "2025-12-12T08:39:19Z",
    "received_at": "2025-12-12T08:39:19.407621Z",
    "labels": {
      "environment": "tutorial"
    }
  }
]

Check delivery attempts

Look at webhook delivery attempts (request attempts) and their status:

curl -X GET "$HOOK0_API/request_attempts/?application_id=$APP_ID" \
  -H "Authorization: Bearer $HOOK0_TOKEN"

Response:

[
  {
    "request_attempt_id": "{REQUEST_ATTEMPT_ID}",
    "event_id": "{EVENT_ID}",
    "subscription": {
      "subscription_id": "{SUBSCRIPTION_ID}",
      "description": "Customer webhook"
    },
    "created_at": "2024-01-15T10:30:01Z",
    "picked_at": "2024-01-15T10:30:02Z",
    "succeeded_at": "2024-01-15T10:30:03Z",
    "failed_at": null,
    "retry_count": 0,
    "response_id": "{RESPONSE_ID}",
    "status": {
      "type": "succeeded",
      "at": "2024-01-15T10:30:03Z"
    }
  }
]

Replay events

You can manually replay an event when needed for business purposes (e.g., re-triggering a workflow). Note that failed deliveries are automatically retried by Hook0:

curl -X POST "$HOOK0_API/events/{EVENT_ID}/replay" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'"
  }'

Advanced patterns

Bulk event processing

When you need to send multiple events (e.g., batch import), send them individually but with correlation:

# Event 1 of batch
curl -X POST "$HOOK0_API/event" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "event_type": "user.account.created",
    "payload": "{\"user_id\": \"usr_789\", \"email\": \"[email protected]\", \"plan\": \"premium\"}",
    "labels": {
      "tenant_id": "customer_123",
      "batch_id": "batch-001",
      "batch_size": "100"
    }
  }'

# Event 2 of batch
curl -X POST "$HOOK0_API/event" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "event_type": "user.account.created",
    "payload": "{\"user_id\": \"usr_7892\", \"email\": \"[email protected]\", \"plan\": \"premium\"}",
    "labels": {
      "tenant_id": "customer_123",
      "batch_id": "batch-001",
      "batch_size": "100"
    }
  }'

Environment-based filtering

Use labels to separate environments:

# Production event
curl -X POST "$HOOK0_API/event" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "event_type": "user.account.created",
    "payload": "{\"user_id\": \"usr_123\"}",
    "payload_content_type": "application/json",
    "occurred_at": "'$(date -u +"%Y-%m-%dT%H:%M:%SZ")'",
    "labels": {
      "tenant_id": "customer_123",
      "environment": "production"
    }
  }'

Response:

{
  "application_id": "{APP_ID}",
  "event_id": "{EVENT_ID}",
  "received_at": "2025-12-12T09:41:39.757315Z"
}

# Staging subscription (will not receive production events)
curl -X POST "$HOOK0_API/subscriptions" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "is_enabled": true,
    "event_types": ["user.account.created"],
    "description": "Staging webhook",
    "labels": {
      "environment": "staging"
    },
    "target": {
      "type": "http",
      "method": "POST",
      "url": "https://staging.example.com/webhook",
      "headers": {
        "X-Environment": "staging"
      }
    }
  }'

Response:

{
  "application_id": "{APP_ID}",
  "subscription_id": "{SUBSCRIPTION_ID}",
  "is_enabled": true,
  "event_types": ["user.account.created"],
  "description": "Staging webhook",
  "secret": "{SECRET}",
  "labels": {
    "environment": "staging"
  },
  "target": {
    "type": "http",
    "method": "POST",
    "url": "https://staging.example.com/webhook",
    "headers": {"x-environment": "staging"}
  },
  "created_at": "2025-12-12T09:41:41.304925Z"
}

Since this subscription filters on environment: "staging", it will not receive the production event above.

Complete integration example

Full flow from event creation to webhook delivery:

Step 1: Create Event Type (one-time setup)

curl -X POST "$HOOK0_API/event_types" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "service": "billing",
    "resource_type": "invoice",
    "verb": "paid"
  }'

Response:

{
  "service_name": "billing",
  "resource_type_name": "invoice",
  "verb_name": "paid",
  "event_type_name": "billing.invoice.paid"
}

Step 2: Create Subscription (customer setup)

curl -X POST "$HOOK0_API/subscriptions" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "is_enabled": true,
    "event_types": ["billing.invoice.paid"],
    "description": "Customer billing webhook",
    "labels": {
      "tenant_id": "customer_789"
    },
    "target": {
      "type": "http",
      "method": "POST",
      "url": "https://customer.example.com/webhooks",
      "headers": {
        "X-Tenant-Id": "customer_789"
      }
    }
  }'

Response:

{
  "application_id": "{APP_ID}",
  "subscription_id": "{SUBSCRIPTION_ID}",
  "is_enabled": true,
  "event_types": ["billing.invoice.paid"],
  "description": "Customer billing webhook",
  "secret": "{SECRET}",
  "labels": {
    "tenant_id": "customer_789"
  },
  "target": {
    "type": "http",
    "method": "POST",
    "url": "https://customer.example.com/webhooks",
    "headers": {"x-tenant-id": "customer_789"}
  },
  "created_at": "2025-12-12T09:43:22.425687Z"
}

⚠️ Save the secret - customers need it to verify webhook signatures.

Step 3: Send Event (when invoice is paid)

curl -X POST "$HOOK0_API/event" \
  -H "Authorization: Bearer $HOOK0_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "application_id": "'"$APP_ID"'",
    "event_type": "billing.invoice.paid",
    "payload": "{\"invoice_id\": \"inv_456\", \"amount\": 1500.00}",
    "payload_content_type": "application/json",
    "occurred_at": "'$(date -u +"%Y-%m-%dT%H:%M:%SZ")'",
    "labels": {
      "tenant_id": "customer_789"
    }
  }'

Response:

{
  "application_id": "{APP_ID}",
  "event_id": "{EVENT_ID}",
  "received_at": "2025-12-12T09:43:24.351417Z"
}

Step 4: Automatic delivery

Hook0 delivers the webhook to https://customer.example.com/webhooks with:

• X-Hook0-Signature header for verification
• The event payload
• Automatic retries on failure

See Implementing Webhook Authentication for signature verification code in Node.js, Python, and Go.

Implementation in other languages

This tutorial uses curl, but here is the same thing in a few languages:

Python

import requests
import uuid
import json
from datetime import datetime, timezone

# Send event
event = {
    "application_id": "{APP_ID}",
    "event_type": "user.account.created",
    "payload": json.dumps({"user_id": "usr_123"}),
    "payload_content_type": "application/json",
    "occurred_at": datetime.now(timezone.utc).isoformat(),
    "labels": {"tenant_id": "customer_123"}
}

response = requests.post(
    "https://app.hook0.com/api/v1/event",
    headers={"Authorization": "Bearer {YOUR_TOKEN}"},
    json=event
)

Go

import (
    "bytes"
    "encoding/json"
    "net/http"
    "time"

    "github.com/google/uuid"
)

// Send event
event := map[string]interface{}{
    "application_id":       "{APP_ID}",
    "event_type":           "user.account.created",
    "payload":              `{"user_id": "usr_123"}`,
    "payload_content_type": "application/json",
    "occurred_at":          time.Now().UTC().Format(time.RFC3339),
    "labels": map[string]string{
        "tenant_id": "customer_123",
    },
}

jsonData, _ := json.Marshal(event)
req, _ := http.NewRequest("POST",
    "https://app.hook0.com/api/v1/event",
    bytes.NewBuffer(jsonData))
req.Header.Set("Authorization", "Bearer {YOUR_TOKEN}")
req.Header.Set("Content-Type", "application/json")

client := &http.Client{}
resp, _ := client.Do(req)
defer resp.Body.Close()

Ruby

require 'net/http'
require 'json'
require 'securerandom'
require 'time'

# Send event
event = {
  application_id: "{APP_ID}",
  event_id: SecureRandom.uuid,
  event_type: "user.account.created",
  payload: {user_id: "usr_123"}.to_json,
  payload_content_type: "application/json",
  occurred_at: Time.now.utc.iso8601,
  labels: {tenant_id: "customer_123"}
}

uri = URI('https://app.hook0.com/api/v1/event')
http = Net::HTTP.new(uri.host, uri.port)

request = Net::HTTP::Post.new(uri)
request['Authorization'] = 'Bearer {YOUR_TOKEN}'
request['Content-Type'] = 'application/json'
request.body = event.to_json

response = http.request(request)

Best practices

1. Event design

• Use semantic naming: service.resource.verb
• Include enough context for consumers to act without extra API calls
• Keep the structure consistent across all events
• Plan for schema evolution from the start

2. Label strategy

• tenant_id: always include for multi-tenancy
• environment: separate prod/staging/dev
• region: geographic filtering when needed

3. Error handling

• Use unique event_id values to prevent duplicates
• Implement retry logic with backoff on your side
• Fail fast when Hook0 is unreachable (circuit breaker)
• Buffer events locally during outages

4. Security

• Never log tokens
• Customers should verify webhook signatures
• Do not send PII in plaintext
• Rate-limit your event sending

Troubleshooting

Event not delivered

# Check if event was received
curl -X GET "$HOOK0_API/events?application_id=$APP_ID" \
  -H "Authorization: Bearer $HOOK0_TOKEN"

# Check subscription filters
curl -X GET "$HOOK0_API/subscriptions?application_id=$APP_ID" \
  -H "Authorization: Bearer $HOOK0_TOKEN"
# Verify labels match your events

401 Unauthorized

# Verify token is included
curl -H "Authorization: Bearer $HOOK0_TOKEN"  # ✅ Correct
curl -H "Authorization: $HOOK0_TOKEN"         # ❌ Wrong - missing Bearer

Event type not found

# List existing event types
curl -X GET "$HOOK0_API/event_types?application_id=$APP_ID" \
  -H "Authorization: Bearer $HOOK0_TOKEN"

# Create missing event type before sending events

Summary

You now know how to:

1. Create event types using the three-part structure
2. Send events with labels for multi-tenancy
3. Create subscriptions with label-based filtering
4. Monitor deliveries and handle failures
5. Process events in bulk

The label system is what makes multi-tenant delivery work without extra complexity. Define types, send events, create subscriptions, check results.

Next steps

• Event Types and Subscriptions Deep Dive
• Webhook Authentication and Security
• Debugging Failed Webhooks
• Multi-Tenant Architecture