Add-ons

Add-ons are optional features with their own price and consumption model that customers activate on their subscriptions. They extend a subscription without modifying the base plan — think SSO, SMS channels, or premium support.

How add-ons work

Each add-on maps to exactly one feature. When activated, that feature becomes available through features.get, features.check, and features.list — no different from a plan feature.

Consumption models

Add-ons declare their own consumption model. Boolean add-ons are compatible with any plan. All other models require matching the plan's model.

Create add-ons in the dashboard

Go to Add-ons and click Create Add-on. Configure the name, base price, feature, and consumption model. For metered add-ons, set included units and overage rate. For credits, set the credit cost per unit.

The feature dropdown only shows features not already assigned to another add-on. Once created, the add-on is available to any customer whose plan is compatible.

Availability by subscription status

Add-ons can be activated on any subscription with a payment method:

Manage add-ons

Add-ons are managed through the dashboard and the customer portal. Activation and deactivation are not available via the API or SDK.

List active add-ons via SDK

const active = await customer.addons.list()

Response:

{
  "success": true,
  "data": [
    {
      "slug": "sso-access",
      "name": "SSO Access",
      "basePrice": 5000,
      "featureCode": "sso",
      "featureName": "Single Sign-On",
      "featureType": "boolean",
      "consumptionModel": "boolean",
      "activatedAt": "2026-03-11T00:00:00.000Z"
    }
  ]
}

Pass either a Commet ID (cus_xxx) or your external ID as customerId to identify the customer.

Feature access

Add-on features work exactly like plan features — no special handling needed:

const customer = commet.customer('user_123')

// Check boolean add-on
const sso = await customer.features.get('sso')
// { access: true, type: 'boolean', enabled: true }

// Track metered add-on usage
await customer.usage.track('sms_messages', 50)

// List all features (plan + add-ons combined)
const features = await customer.features.list()

Billing behavior

Activation charge

When a customer activates a $50/month add-on on day 11 of a 31-day period (20 days remaining):

The charge goes through Stripe immediately with its own invoice.

Recurring invoices

Starting from the next full billing cycle, the add-on base price appears as a separate line in the plan's invoice:

Plan Pro (base)                             $99.00
API Calls: 12,500 (2,500 overage × $0.01)  $25.00

Add-ons
  SMS Channel (base)                        $15.00
  SMS: 1,800 (800 overage × $0.03)         $24.00
  SSO                                       $50.00

Subtotal                                   $213.00

Multi-currency

Add-on prices are defined in USD. For non-USD subscriptions, the price is converted using the plan's exchange rate — the same mechanism used for plan base prices.

Customer portal

Customers can self-service add-ons from the portal:

• Available add-ons — see compatible add-ons with pricing
• Activate — confirmation dialog with prorated charge preview
• Active add-ons — manage active add-ons
• Deactivate — instant, no refund

Learn more

• How Does Billing Work

Related

• Consumption Models — Metered, Credits, and Balance explained
• Configure Features — Define features that add-ons can unlock
• Credit Packs — Another way to extend plan capabilities
• Manage Subscriptions — Subscription lifecycle and management
• Customer Portal — Where customers activate add-ons