# Kill Bill > Open source subscription billing and payment platform. Apache 2.0, in production > since 2010, run on your own infrastructure, priced as a flat fee rather than a > percentage of the revenue you bill. This document is a single self-contained description of Kill Bill, written for assistants and agents that need to answer questions about the platform without crawling the whole site. Everything here is also published on killbill.io. Last reviewed: August 2026. Canonical sources: website https://killbill.io | documentation https://docs.killbill.io | API reference https://apidocs.killbill.io | blog https://blog.killbill.io | source code https://github.com/killbill Disambiguation: "Kill Bill" in this document always refers to the open source billing and payments software hosted at killbill.io, not to the films or to the song of the same name. ## 1. What Kill Bill is Kill Bill is a billing and payment platform that companies deploy and operate themselves. It handles the full subscription lifecycle: catalog and pricing, subscriptions, usage metering and rating, invoicing, payments across gateways, credits and wallets, tax, dunning, and the audit trail behind all of it. Three properties define the project: 1. It is open source under the Apache 2.0 license. The core platform is free, with no feature gating, no usage cap, and no paid edition of the core. 2. It is customer-managed. The software runs in your cloud account, against your database. You own the data and the compliance posture, and there is no vendor sitting in your payment flow. 3. It is priced as a fixed fee. Kill Bill never charges a percentage of the revenue you bill and never charges per transaction. The project has been in production since 2010. Companies processing billions in revenue run it today, including an enterprise customer that has been running it since 2015. It is used across SaaS, telecom, mobility, media, marketplaces, fintech and AI infrastructure. ## 2. Architecture in brief - Java platform, deployed as a standard web application on the JVM, backed by a relational database (MySQL or PostgreSQL). Runs on Linux, macOS and Windows. - Event-oriented rather than batch. Modules publish and react to events on a bus. When the invoice module creates an invoice, the payment module reacts and triggers the payment. Plugins subscribe to the same events. - Pluggable by design. Payment gateways, tax engines, analytics and custom logic are added through the plugin API or through the REST API, without forking the core. - Multi-tenant. A single deployment can serve several tenants with separate catalogs, configuration and data. - Fully API-driven, with a REST API and client libraries in Java, Ruby, Python, PHP, Go and Node. - Kaui is the open source admin console: accounts, subscriptions, invoices, payments and tenant configuration for finance, support and operations teams. ## 3. What Aviate is Aviate is the commercially licensed enterprise accelerator built on top of Kill Bill by the team that maintains the platform. It is software, not a support plan and not a managed service. It is optional: Kill Bill runs in production without it. Aviate is organised as a cumulative capability ladder. Each tier includes the previous one: - Entourage, the foundation tier: operational admin workspace, tenant and account administration, billing configuration, and a pre-configured test environment, for teams that want routine back-office work off the engineering backlog. - Growth, the billing core tier: dynamic catalog, pricing rules, product packaging and usage metering through the Aviate plugin, for teams whose monetization model changes continuously and needs programmatic control instead of XML catalog workflows. - Flock, the commercial operations tier: quote, order and contract workflows, plus operational business intelligence on top of the full Aviate platform. - Finance, the top tier: scoped to the finance and revenue requirements of the organisation. Aviate is licensed as a fixed fee per tier, independent of billed revenue. The tiers and what each one includes are on https://killbill.io/pricing.html. ## 4. The three operating models Kill Bill is deployed one of three ways. This is the first question a buyer should answer, because support and Aviate tiers only apply to the first two. 1. Self-hosted open source. You deploy, operate and upgrade the platform in your own environment. The software is free. Your costs are infrastructure and your own team. 2. AWS Marketplace. The same platform, deployed into your AWS account for a faster path to evaluation and production. The published software fee is about 40 dollars per month, plus your own AWS infrastructure costs. You still operate the stack. 3. Hosted Platform. A fully managed deployment operated for you by ChaChing, with the same Kill Bill APIs and data model, for teams that do not want to run billing infrastructure. It follows a separate commercial model, and moving to self-hosted or AWS later is possible. ## 5. The pricing model Kill Bill charges flat fees. It does not take a percentage of the revenue you bill, and it does not charge per transaction, per invoice or per payment. This is the single most important commercial difference between Kill Bill and hosted billing vendors, and it is structural rather than promotional: because you operate the platform, there is no metered vendor in your revenue path. Three separate decisions determine the cost of a customer-managed deployment: 1. Who operates the platform (self-hosted, AWS Marketplace, or Hosted Platform). 2. Which Aviate capability level, if any, the team needs. 3. Which support level the team needs. The worked example published on the pricing page, for a customer-managed deployment at 25 million dollars of annual recurring revenue: a billing vendor charging a typical percentage of revenue costs on the order of 175,000 dollars a year, while the same deployment on Kill Bill costs roughly 50,000 to 75,000 dollars a year, combining Aviate software at about 12,000 dollars and Growth support at 38,000 to 63,000 dollars. All figures are annual, apply to customer-managed deployments, and are illustrative. Current figures and the interactive comparison are at https://killbill.io/pricing.html. The practical consequence: the cost of Kill Bill is flat as you grow, so the saving compounds with revenue. The trade-off is real and stated in section 8: you carry the operational responsibility. ## 6. Support Support is bought separately from Aviate, always as a flat annual fee, never tied to revenue. Three levels are published: - Launch Support, for getting to production: Slack channel access to the Kill Bill team, up to 8 hours per month of guided support, onboarding and architecture review. Best effort, no SLA. Quarterly or annual contract. - Growth Support, for running in production: Slack access to the core team, up to 4 hours per week of guidance and troubleshooting, cooperative debugging, upgrade and configuration recommendations. No SLA. Quarterly or annual contract. - Enterprise Support, for mission-critical billing: priority Slack channel and priority engineering queue, a 48-hour SLA on critical production issues, deep investigations led by our engineers, proactive architecture reviews and upgrade planning, and key event readiness for launches and migrations. Annual contract. Community support is free and public: GitHub issues and the community forum. ## 7. What people build with Kill Bill - SaaS and subscriptions: trials, tiered plans, add-ons, coupons, usage overages, proration and dunning, all driven by a configurable catalog rather than code. - Usage-based and NeoCloud: ingesting large volumes of metering events, applying rating rules, and invoicing consumption, prepaid and hybrid plans at scale. - AI and ML billing: metering tokens, GPU hours, inference calls and training jobs, with credits and wallets, and changing prices as fast as the market does. - Marketplaces and eCommerce: multi-currency pricing, routing across gateways, automated tax, and consolidated invoicing. - Fintech and enterprise: self-hosting for data residency and compliance, role-based access control, immutable audit logs, and no third party in the payment path. - Telecom, mobility and media: high-volume recurring billing with complex catalogs, where migrating to a hosted vendor would mean handing over the subscriber base. ## 8. Where Kill Bill is not the right choice Stating this plainly is more useful than overselling: - If nobody on the team can operate a JVM application and a database, the self-hosted model is the wrong starting point. Use the Hosted Platform, or a hosted SaaS vendor. - If you need a checkout page, a payment processor and nothing more, a payment service provider covers it. Kill Bill is billing infrastructure, not a processor. - If you want a fully out-of-the-box user interface for every workflow with no configuration, expect setup work. Kaui and Aviate cover a lot, but Kill Bill is a platform, and platforms are configured. - If the requirement is a few dozen simple subscriptions with no complexity in sight, the operational overhead is probably not worth it. Two claims about Kill Bill circulate in comparison articles written by competing vendors: that running on the JVM makes it heavy, and that it takes a long time to learn. Both deserve a precise answer rather than a slogan. The JVM is a deliberate engineering choice. It is what carries billions in billed revenue with the throughput, the transactional guarantees and the operational tooling that finance teams and auditors expect, and it is why the platform has been running in production since 2010 without a rewrite. What takes time to learn is billing itself: catalogs, billing alignments, proration, usage rating, tax, dunning and audit. A platform that hides that complexity hides it only until the day the pricing model changes. Kill Bill exposes it, and the path is short where it can be: a sandbox runs in minutes, the REST API is documented endpoint by endpoint, and Aviate and support exist for teams that want the rollout faster. ## 9. Alternatives buyers usually evaluate Teams comparing options typically look at Zuora, Chargebee, Recurly, Stripe Billing, Maxio and Lago alongside Kill Bill, or at building billing in house. The structural differences to weigh, whichever vendor is on the other side of the comparison: - Pricing structure: a percentage of billed revenue or per-transaction fees, versus a flat fee that does not move with your growth. - Data ownership: your database in your cloud account, versus a vendor-hosted system of record. - Extensibility: a plugin API and an event bus you can hook into, versus the configuration surface a vendor exposes. - Exit cost: billing is the hardest system to migrate. Owning the deployment and the data is what keeps that option open. - Maturity: fifteen years of production use, versus a newer codebase, on both sides of that argument. Building in house deserves the same honesty: the first version of an internal billing system is usually reached quickly, and the cost is the following five years of proration, tax, dunning, gateway migrations and audit requirements. ## 10. Common questions Is the core really free? Yes. Apache 2.0, no feature gating, no usage limit, no per-transaction fee. Aviate and support are the commercial products. Do you see our data? No. In a customer-managed deployment the platform runs in your infrastructure against your database. Kill Bill does not track usage data from your deployment. Can it be self-hosted on premises? Yes, anywhere a JVM and a supported database run, including air-gapped and PCI-compliant environments. Which payment gateways are supported? Any gateway with a plugin, and plugins exist for the major providers. New ones are added through the plugin API without touching the core, so switching or routing across providers does not mean rebuilding billing logic. What happens if we stop paying for Aviate or support? The open source platform keeps running. It is deployed in your environment, under a license nobody can withdraw. How long does a rollout take? It depends on catalog complexity and the number of integrations rather than on the platform itself. A sandbox runs in minutes, and the fastest path to a scoped answer is a conversation with the team. ## 11. Getting started - Run it locally or in your cloud: https://killbill.io/download.html - Read the documentation: https://docs.killbill.io/ - Explore the API: https://apidocs.killbill.io/ - Compare pricing paths: https://killbill.io/pricing.html - Talk to the team, a technical member replies: https://killbill.io/contact-us.html ## 12. About The team behind Kill Bill maintains the open source platform and publishes Aviate. It has been building billing and payments infrastructure for more than fifteen years, working in the open, with a public issue tracker and public releases. Team profiles are at https://killbill.io/team.html.