> ## Documentation Index
> Fetch the complete documentation index at: https://docs.flexprice.io/llms.txt
> Use this file to discover all available pages before exploring further.

# COUNT UNIQUE

> Counts the number of distinct values for a specified property.

Step-by-Step Setup when creating a COUNT UNIQUE-based metered feature:

1. **Navigate to Features**
   * Go to Product Catalog → Features
   * Click "Add Feature"

2. **Basic Information**
   * **Name**: "Active Users" (or descriptive name)
   * **Type**: Select "Metered"

3. **Event Configuration**
   * **Event Name**: `user.activity` (must match your event data)
   * **Aggregation Function**: Count Unique
   * **Aggregation Field**: `user_id` (the property to count unique values for)

4. **Usage Settings**
   * **Usage Reset**: Periodic (for monthly limits) or Cumulative
   * **Unit Name**: `user / users`

5. **Save Feature**

## Calculation Example

### Event Data

```json theme={null}
[
  {
    "event_id": "evt_001",
    "event_name": "user.activity",
    "external_customer_id": "customer_123",
    "timestamp": "2024-01-15T10:00:00Z",
    "properties": {
      "user_id": "user_alice"
    }
  },
  {
    "event_id": "evt_002", 
    "event_name": "user.activity",
    "external_customer_id": "customer_123",
    "timestamp": "2024-01-15T10:05:00Z",
    "properties": {
      "user_id": "user_bob"
    }
  },
  {
    "event_id": "evt_003",
    "event_name": "user.activity",
    "external_customer_id": "customer_123", 
    "timestamp": "2024-01-15T10:10:00Z",
    "properties": {
      "user_id": "user_alice"
    }
  },
  {
    "event_id": "evt_004",
    "event_name": "user.activity",
    "external_customer_id": "customer_123", 
    "timestamp": "2024-01-15T10:15:00Z",
    "properties": {
      "user_id": "user_charlie"
    }
  }
]
```

### Calculation Process

1. **Event Matching**: All events with `event_name = "user.activity"`
2. **Property Extraction**: Extract `user_id` values from each event
   * `evt_001` → `"user_alice"`
   * `evt_002` → `"user_bob"`
   * `evt_003` → `"user_alice"` (duplicate)
   * `evt_004` → `"user_charlie"`
3. **Count Unique Result**: `3` distinct users (`user_alice`, `user_bob`, `user_charlie`)

**Result**: `3 users`

## Use Cases

### Active Users Tracking

**Perfect for**: Monthly active users, daily active users, unique visitors

```json theme={null}
{
  "event_name": "user.activity",
  "external_customer_id": "acme_corp",
  "properties": {
    "user_id": "user_12345"
  }
}
```

### Unique Sessions

**Perfect for**: Session tracking, device identification, unique connections

```json theme={null}
{
  "event_name": "session.activity",
  "external_customer_id": "user_456",
  "properties": {
    "session_id": "sess_abc123"
  }
}
```

### Feature Usage

**Perfect for**: Unique feature users, distinct tool usage, unique resource access

```json theme={null}
{
  "event_name": "feature.usage",
  "external_customer_id": "merchant_789",
  "properties": {
    "feature_name": "advanced_analytics"
  }
}
```

### IP Address Tracking

**Perfect for**: Unique IP addresses, geographic distribution, security monitoring

```json theme={null}
{
  "event_name": "api.request",
  "external_customer_id": "customer_101",
  "properties": {
    "ip_address": "192.168.1.100"
  }
}
```

### Device Tracking

**Perfect for**: Unique devices, platform analytics, hardware usage

```json theme={null}
{
  "event_name": "app.usage",
  "external_customer_id": "mobile_user",
  "properties": {
    "device_id": "device_xyz789"
  }
}
```

### When to Use COUNT UNIQUE

✅ **Use COUNT UNIQUE when:**

* Tracking distinct users, sessions, or resources
* Need to count unique values, not occurrences
* Measuring reach or adoption metrics
* Eliminating duplicates for billing purposes

## Next Steps

* **[Creating a Metered Feature](/docs/event-ingestion/creating-a-metered-feature)** - Complete setup guide
* **[Sending Events](/docs/event-ingestion/sending-events)** - How to transmit COUNT UNIQUE events