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Help customers understand the financial impact of their actions before they commit to taking them. The preview events endpoint allows you to simulate how events would affect a customer’s invoice without actually processing or billing for them.

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Why preview costs?

Cost transparency builds trust and empowers customers to make informed decisions. Common scenarios include:
  • Resource-intensive operation cost previews: Show users how much a compute job or data processing task will cost before confirming execution
  • Budget planning: Help customers forecast costs for planned usage patterns with interactive cost calculators
  • What-if analysis: Let customers explore different usage scenarios to optimize their spending

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How cost preview works

The preview events endpoint evaluates events against a customer’s actual contract configuration, including all pricing complexity:
  • Tiered pricing: Correctly applies volume discounts and tier transitions
  • Commits and credits: Shows what usage is covered by commit and credit balances and what spills into overage
  • Free allotments: Accounts for included usage in the contract
  • Multiple products: Calculates costs across all products in the contract

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Preview modes

There are two different ways you can choose to evaluate preview events:

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Merge mode

Combines preview events with the customer’s existing usage for the billing period. Use this to show incremental cost impact. Example: A customer has used 99 API calls this month (with 100 free). Previewing 5 calls in merge mode shows 1 free and 4 billable.

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Replace mode

Evaluates only the preview events, ignoring existing usage. Use this for hypothetical “clean slate” scenarios. Example: Show the total monthly cost if a customer only performed the specific actions in the preview.

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Set up a cost preview

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Basic example

Preview how 100 compute hours would affect a customer’s invoice: 
curl --request POST \
  --url https://api.metronome.com/v1/customers/{customer_id}/previewEvents \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
    "events": [
      {
        "event_type": "compute_usage",
        "timestamp": "2025-11-15T10:00:00Z",
        "properties": {
          "compute_hours": "100",
          "instance_type": "gpu-large"
        }
      }
    ],
    "mode": "merge"
  }'

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Response structure

The endpoint returns draft invoices showing the calculated costs: 
{
  "data": [
    {
      "id": "68e0bc1c-a8ec-5765-856b-f896285b4cdb",
      "issued_at": "2025-12-02T12:00:00+00:00",
      "start_timestamp": "2025-11-01T00:00:00+00:00",
      "end_timestamp": "2025-12-01T00:00:00+00:00",
      "customer_id": "46b2c479-6202-4db6-b392-5a156a9dd5c8",
      "customer_custom_fields": {
        "bill_customer_id": "0du01JDIRIUDQKDS6wm2"
      },
      "type": "USAGE",
      "credit_type": {
        "id": "2714e483-4ff1-48e4-9e25-ac732e8f24f2",
        "name": "USD (cents)"
      },
      "status": "DRAFT",
      "total": 49000,
      "external_invoice": null,
      "contract_id": "688d9619-bd2c-42db-8dcb-288f02f741df",
      "contract_custom_fields": {},
      "line_items": [
        {
          "product_id": "c2ab408b-d212-4dca-a99b-f2b450abad45",
          "product_type": "UsageProductListItem",
          "product_custom_fields": {
            "org_id": "prod_NbZryAoW6ugALt"
          },
          "product_tags": [
            "compute"
          ],
          "name": "GPU Compute Hours",
          "type": "usage",
          "total": 0,
          "credit_type": {
            "id": "2714e483-4ff1-48e4-9e25-ac732e8f24f2",
            "name": "USD (cents)"
          },
          "starting_at": "2025-11-01T00:00:00+00:00",
          "ending_before": "2025-12-01T00:00:00+00:00",
          "netsuite_item_id": "f2b4-50ab-ad45",
          "unit_price": 4900,
          "quantity": 10
        }
      ],
      "custom_fields": {},
      "billable_status": "billable"
    }
  ]
}
For customers with multiple active contracts, the endpoint returns separate invoices for each: 
{
  "data": [
    {
      "contract_id": "contract-1-id",
      "total": 50000,
      // ... invoice details for contract 1
    },
    {
      "contract_id": "contract-2-id",
      "total": 25000,
      // ... invoice details for contract 2
    }
  ]
}

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Event deduplication

The preview endpoint follows the same deduplication logic as the ingest endpoint:
  • Events with identical transaction_id values passed in the same request payload are deduplicated against each other
  • Events with identical transaction_id values to those passed to /ingest in the prior 34 days are deduplicated as well

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Best practices & limitations

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Performance considerations

The endpoint has an 8 RPS rate limit per client and is not suitable for real-time validation of every event. Consider these strategies:
  • Cache preview results: When showing repeated calculations for similar usage patterns, cache the results
  • Batch multiple events: Preview multiple events in a single request rather than making separate calls

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Accuracy tips

  • Include all relevant event properties that affect pricing
  • Test both merge and replace modes during development

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Limitations

  • Customers using SQL-based billable metrics cannot use this endpoint. If SQL BMs are present on the customer invoice being evaluated when passing in events to preview, the endpoint will return a 400 error.