Lago

Lago is an open-source metering and usage-based billing platform built for modern software companies, especially those with complex or consumption-based pricing. As more SaaS and AI products move away from simple flat subscriptions toward usage-based, hybrid and tiered models, billing becomes genuinely hard to build and maintain. Lago tackles this head-on, providing a flexible billing engine that handles metering events, applying pricing logic, and generating invoices — all available as open source you can self-host or use in the cloud.

The platform's core is its event-based metering and pricing system. Lago ingests usage events from your product, aggregates them, and applies whatever pricing structure you need — per-seat, per-usage, tiered, volume, packages, prepaid credits, add-ons and combinations thereof. This flexibility is exactly what teams struggle to build in-house, where billing code becomes a sprawling, error-prone mess. Lago centralizes that logic in a dedicated, battle-tested system, then handles invoicing, coupons, taxes and integrations with payment providers and your finance stack.

Being open source is a major differentiator. Companies that care about data control, customization or avoiding the high fees and lock-in of closed billing platforms can self-host Lago and shape it to their needs, while still benefiting from an active community and ongoing development. It's particularly popular with developer-led and API-first companies, including many in the AI space, where usage-based pricing is the norm and accurate metering is critical to revenue. For engineering and finance teams who find building billing in-house painful and proprietary platforms expensive or inflexible, Lago offers a powerful, transparent and adaptable foundation. It represents a modern, open approach to one of software's least glamorous but most important problems: getting paid accurately for what customers actually use.