# Kill Bill > Open source subscription billing and payment platform. Apache 2.0, in production > since 2010, free, run on your own infrastructure. Aviate is the enterprise > offer, 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: October 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. ## Key facts - License: Apache 2.0. Free, no license fee, no fee per transaction. - In production since 2010. Deployments on the platform have invoiced billions of dollars since then. - Deployment: self-hosted, with Docker, in Tomcat or on Kubernetes, in any cloud or data center. - Databases: MySQL, MariaDB or PostgreSQL. - Language: Java. Plugins are written in Java. - Admin UI: Kaui, open source. Aviate has its own interface. - Payment plugins: Stripe, Adyen, Braintree, Hyperswitch, plus your own. - Tax plugins: Avalara AvaTax, Vertex, Kintsugi. Aviate Tax adds rates per country and per product. - Support: community for the open source version, without SLA. Level 3 support from the engineers with Aviate. - Enterprise offer: Aviate, 9,999 USD per month, billed annually, never a share of revenue. ## 1. What Kill Bill is Kill Bill is a subscription billing and payment platform that companies deploy and operate themselves. It handles the full subscription lifecycle: catalog and pricing, subscriptions, usage billing, invoicing, payments across gateways, credits, 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. Its enterprise offer, Aviate, 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. It is used across SaaS, telecom, mobility, media, marketplaces, fintech and AI infrastructure. ## 2. Architecture in brief - Java platform, deployed as a web application on the JVM, backed by a relational database (MySQL, MariaDB or PostgreSQL). The official Docker images start Kill Bill, Kaui and a database with one docker-compose.yml file. - 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, and push notifications send them to your own endpoints. - 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. Open source plugins exist for payment gateways such as Stripe, Adyen, Braintree and Hyperswitch, and for tax engines such as Avalara AvaTax, Vertex and Kintsugi. - Multi-tenant. A single deployment can serve several tenants, each with its own catalog, configuration, API credentials and data. - Stateless nodes. You add nodes behind a load balancer as the load grows. - Fully API-driven, with a REST API and client libraries in Java, Ruby, Python, PHP, Go and JavaScript. - Kaui is the open source admin UI: accounts, subscriptions, invoices, payments, refunds, tenants, catalog upload, users, roles and plugins, for finance, support and operations teams. ## 3. Features Open source Kill Bill: - Catalog and pricing: plans, phases such as free trials, add-ons, price lists and several currencies, in an XML catalog. - Subscriptions: create, change, pause, resume and cancel, with change policies and proration. - Usage billing: usage priced in tiers or blocks, billed in arrears. - Invoicing: invoices generated as events happen and on billing dates, with credits, adjustments, draft invoices and dry runs. - Payments: one payment API across gateways, with authorize, capture, purchase, refund and chargeback transactions. - Retries and dunning: retry schedules for failed payments, then overdue states that block changes or pause the service. - Tax: through tax plugins. - Multi-tenancy, audit logs (who changed what, when, and why), tags and custom fields, plugins, push notifications, and reports through the analytics plugin. - Roles and permissions, with users from the Kill Bill database, LDAP or Active Directory, Okta or Auth0. Aviate adds: - A catalog editor for plans, phases and prices. - Aviate Coupons, Aviate Wallet (prepaid credits), Aviate Metering (usage event ingestion) and Aviate Tax (rates per country and per product). - Custom invoice sequencing, per tenant or per account. - Aviate Health: node metrics, stuck bus and notification entries, diagnostic reports. - The Aviate interface, and Level 3 support. Feature list: https://killbill.io/solutions.html ## 4. What Aviate is Aviate is the enterprise version of Kill Bill, with added features. It is built on top of the open source platform by the team that maintains it. Aviate is for companies with complex billing needs: multiple pricing models, high volumes, several entities or currencies, and strict finance and audit requirements. Aviate includes two things: - The Aviate commercial license, with the modules listed above. - Level 3 support through a dedicated Slack channel, where you talk directly to the engineers who build and maintain the platform. P1 issues get a response within 1 business day. Aviate costs 9,999 USD per month, billed annually, independent of billed revenue. It runs where the customer chooses: any cloud or its own infrastructure. A free hosted sandbox lets you try Aviate in a browser: https://aviate.killbill.io/. Details are on https://killbill.io/aviate.html. ## 5. The two ways to run Kill Bill Kill Bill is deployed one of two ways. This is the first question a buyer should answer. 1. Open source, self-hosted. You deploy, operate and upgrade the platform in your own environment. The software is free. Your costs are infrastructure and your own team. There is no support and no SLA: help comes from the community. 2. Aviate. The same platform, plus the Aviate modules and Level 3 support from the engineers, for 9,999 USD per month, billed annually. It runs in any cloud or on your own infrastructure. To start: https://killbill.io/download.html. The Docker quick start runs Kill Bill on port 8080 and Kaui on port 9090 in a few minutes, with at least 4 GiB of memory for Docker. ## 6. 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. The cost of a deployment comes down to one decision: run the open source platform on your own, for free, or take Aviate at 9,999 USD per month, billed annually. Current pricing is 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: you carry the operational responsibility. ## 7. Support The open source platform comes with no support and no SLA. Community help is free and public: the Kill Bill users mailing list (https://groups.google.com/g/killbilling-users) and GitHub issues (https://github.com/killbill). Support is part of Aviate: Level 3 support through a dedicated Slack channel, where you talk directly to the engineers who build and maintain the platform, with a response within 1 business day for P1 issues. The Kill Bill team does not build custom plugins. Partners do: see section 10. ## 8. 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: metering events, rating rules, and invoicing consumption, prepaid and hybrid plans. - AI and ML billing: tokens, GPU hours, inference calls and training jobs, with prepaid credits, and prices that change as fast as the market does. - Marketplaces and eCommerce: multi-currency pricing, several gateways, automated tax, and many tenants in one deployment. - Fintech and enterprise: self-hosting for data residency and compliance, roles and permissions, 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. ## 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: in production since 2010, 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. Open source is not the right fit for every team: without engineers who can run a Java service, or when a hosted tool must work the same day, a hosted SaaS billing tool is often simpler. Guide: https://killbill.io/how-to-choose-a-billing-software-system.html ## 10. Partners - ChaChing: hosted Kill Bill platform. - Wovenware: custom plugins and integrations. - Bill Rush: commercially supported Kill Bill distribution on Kubernetes. - Numerio: Kill Bill QA Suite, a testing tool built for Kill Bill. - Avalara: tax (AvaTax plugin) and e-invoicing. - Forte: ACH payments. Details: https://killbill.io/customized-billing-system.html ## 11. Common questions Is the core really free? Yes. Apache 2.0, no feature gating, no usage limit, no per-transaction fee. Aviate is the commercial offer. Do you see our data? No. In a customer-managed deployment the platform runs in your infrastructure against your database, so your billing data stays with you. Can it be self-hosted on premises? Yes, anywhere a JVM and a supported database run. Kill Bill runs today in PCI DSS compliant companies; with gateway tokenization, card data stays with the payment gateway. Which payment gateways are supported? Any gateway with a plugin. Open source plugins exist for Stripe, Adyen, Braintree and Hyperswitch. New ones are added through the plugin API without touching the core, so switching or adding providers does not mean rebuilding billing logic. What happens when a payment fails? For invoice payments, Kill Bill retries on a schedule you set per tenant, by default three retries 8 days apart. If the invoice stays unpaid, overdue rules can block changes or pause the service. What happens if we stop paying for Aviate? 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 local install runs in minutes, and the fastest path to a scoped answer is a conversation with the team. More answers: https://killbill.io/faqs.html ## 12. Getting started - Run it locally or in your cloud: https://killbill.io/download.html - Try Aviate in a browser: https://aviate.killbill.io/ - Read the documentation: https://docs.killbill.io/ - Explore the API: https://apidocs.killbill.io/ - Learn about Kaui: https://killbill.io/kaui.html - See Aviate pricing: https://killbill.io/pricing.html - Talk to the team, a technical member replies: https://killbill.io/contact-us.html ## 13. About The team behind Kill Bill maintains the open source platform and publishes Aviate. It has built billing and payments infrastructure since 2010, working in the open, with a public issue tracker and public releases. Team profiles are at https://killbill.io/team.html.