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getlago/lago
Open Source Metering and Usage Based Billing API ⭐️ Consumption tracking, Subscription management, Pricing iterations, Payment orchestration & Revenue analytics
Lago is a self-hostable billing platform targeting companies with usage-based or hybrid pricing models — think AI API companies billing per token, or SaaS with seat + consumption pricing. It handles event ingestion, subscription management, invoicing, dunning, and revenue analytics. YC-backed, used by Mistral and Groq, so it's battle-tested at real scale.
The event processing pipeline is a proper Go service backed by Kafka with Redis caching for billing metric lookups — not an afterthought. The polyglot architecture makes sense: Go for high-throughput event ingestion, Ruby for the business logic API, React for the UI. ClickHouse integration for analytics is the right call for time-series billing data. AGPLv3 is an honest license choice that doesn't pretend to be open while protecting a cloud moat.
The self-hosted stack is genuinely heavy: Postgres, Redis, Kafka, ClickHouse, and multiple Docker services — this is not something you spin up on a $10 VPS. The 'api' and 'front' directories are git submodules pointing to separate repos, so the monorepo is a facade; you're actually coordinating across three codebases. The AGPL license will block adoption at any company with legal worried about copyleft in their billing layer, and those companies are exactly Lago's target market.