Design Considerations for Your Billing API

Exposing a billing API for usage-based SaaS companies is essential for providing customers with access to their cost data, but it presents numerous challenges and considerations. Each cloud service provider, such as AWS, Azure, and Google Cloud, offers varying methods for accessing billing data, each with its own level of complexity and data freshness. Billing data is unique, not quite fitting into traditional financial or engineering metrics, and is often overwritten rather than append-only. Key considerations in developing a billing API include managing data cardinality, handling upfront commitments, credits, and discounts, and ensuring proper authentication and data transfer capabilities. The implementation must also account for data size and how customers will access this information, with examples from MongoDB, Snowflake, and AWS illustrating different approaches. Despite the complexities, providing transparent access to billing data is beneficial for customers and aligns with the trend of integrating finance and engineering in cloud environments.