Frequently Asked Questions

Everything you ever wanted to know about Kill Bill

About Kill Bill

What is Kill Bill software?
Kill Bill is an open-source programmable platform that enables you to build custom billing solutions. That’s a mouthful, to say the least, but think of it as building blocks to implement your own billing workflows.
Similar to the Unix philosophy of composability over monolithic design, Kill Bill provides APIs to create various pricing models, manage subscriptions, generate invoices, integrate with various payment gateways, etc. Whether you are selling access to a digital service for $10 a month or selling a multi-tier cell-phone data plan, Kill Bill provides the primitives to do it so you don’t have to start from scratch.
Who created Kill Bill?
Martin Westhead, Pierre-Alexandre Meyer and Stéphane Brossier designed and developed Kill Bill in 2010 as part of an open-source project at Ning.
How long has Kill Bill been around?
Since 2010, Kill Bill has been running in production in private and public companies, invoicing billions of dollars and charging millions of credit cards.
Can I really use Kill Bill for free?
Yes. The Kill Bill open-source software is completely free! Just make sure you follow the Apache License, Version 2.0.
How is Kill Bill different from other billing software?

Contrary to any SaaS solution:

  • Kill Bill is open-source. Read more: Why open-source software?
  • Kill Bill has a pluggable architecture, allowing you to write plugins (i.e., custom code) to extend or change default behaviors.
  • Kill Bill is not a batch system by default. Instead, it uses an event-oriented architecture. Modules share and react to events. For example, whenever a new invoice is generated, the invoice module sends an invoice creation event on the message bus. The payment module reacts and triggers the actual payment. These events are available to plugins, so you can write custom logic the same way.
  • Because you host your own instances, you are in full control of your data. (See also “Do you track any usage data in Kill Bill?”)
Does Kill Bill work with [software name]?
Over the years, Kill Bill has been customized (either with plugins or additional logic) to work with many different types of software (for example, customer relationship management software (CRMs) and financial accounting software). If you’re interested in exploring this option, contact our software development partner for more information.
Can I contribute to Kill Bill?
We’d love to talk to you about this. Please get in touch with us.
Is there a Kill Bill demo?
We have a self-directed demo that you can access here. You can click around in Kaui, the administrative user interface for Kill Bill. If you’re interested in a high-level overview, see these two short videos on Kill Bill and Kaui.
Why did you name your software after a famous Quentin Tarantino movie?
We were enamored with the idea of “killing the billing problem.” Secondly, we like the Kill Bill movie!
Why do you have a duck as a company mascot?
Why do you have a duck as a company mascot?
Kill Bill logo
P.S. His name is Killian!
Are there any rules for using Kill Bill (since it's open-source)?
All of the “rules” are covered in an open-source license. Kill Bill uses the Apache Version 2.0 license. Of course, there are many details, but we’ve summarized it here: Why Open-Source?
I’m a software consultant/shop. Can I implement Kill Bill for my customers?
Yes, others have used Kill Bill as white label software. The source code has a permissive Apache Version 2.0 license, and you can hide the Kill Bill brand from the API and user interface. If you need further information, please feel free to contact us.
What is Kaui?
Kaui is a browser-based application that enables back-office staff (in Finance, Marketing, Development, etc.) to perform Kill Bill-related tasks, such as creating customer accounts, subscriptions, adding plugins, and so forth. “Kaui” (KAUI) stands for Kill (Bill) Admin User Interface. For more information, see the Kaui User Guide.
Why should I choose Kill Bill over a SaaS alternative?

Using a SaaS solution (for example, Zuora or Chargebee) seems like a smart business decision. These types of SaaS billing solutions have been around for several years, know their clients’ needs, and often give the impression that they can solve all of your billing problems.

But just as there are benefits to using a SaaS billing solution, there are also disadvantages, and they aren’t minor. The largest disadvantage is if you work with a SaaS billing provider, all of the data associated with your revenue is in their hands – not yours. That precious data can even be difficult to access at times, believe it or not.

Before you lock yourself into a SaaS subscription billing vendor, consider the following:

  • Restrictions in integrating with existing business software (accounting, CRM, etc.)
  • Limited feature sets
  • Limited choices in third-party providers, such as for payment processing, tax calculation, fraud detection, etc.
  • Issues with testing (limited number of sandboxes at a high cost)
  • Inadequate analysis and reporting solutions (i.e., holding your data hostage)

To read more about this, see our article, The Pitfalls of a SaaS Billing and Payments Solution.

Do you have customers in [country name] or in [specific industry] that are using Kill Bill? Can you put me in touch with them?
You can certainly contact us to ask, but Kill Bill users we’ve worked with in the past often restrict us from disclosing this information. We recommend you post this type of question on the Kill Bill Community (mailing list), which is quite active.
Can I see a list of companies that use Kill Bill?
This image from our website displays logos of just some of the organizations that use Kill Bill. We know that the number of Kill Bill installations numbers in the thousands. However, the businesses that use Kill Bill prefer to keep that information private because they view Kill Bill as a competitive advantage.
What kind of support do you offer?
Our main support is offered via the Kill Bill Community (mailing list). The Kill Bill core team monitors it regularly, and it’s suitable for relatively simple problems.
If you need a short-term consultation, you can sign-up for that directly on our Support page. Offered via Slack, these four-hour consultations are intended to help to solve a difficult problem with Kill Bill, discuss if Kill Bill can fulfill your requirements, and discuss topics of that nature.
You can also contact us if you have more specific needs.
How robust is Kill Bill?
Kill Bill is robust enough that Groupon uses it to handle transactions and payments, with a global revenue of about $967 million (USD) in 2021. In the first quarter of 2022, Groupon processed 22.2 million transactions (Statistica).
We’re very confident that Kill Bill can handle the demands of most businesses. To read more on this topic, check out our blog posts On Kill Bill performance and Performance Numbers.


Is Kill Bill a Software-as-a-Service (SaaS)?
Kill Bill is not SaaS. It is open-source software that you can run in your own environment, a private data center, or in the cloud (AWS, Azure, etc.).
Can you run Kill Bill in the cloud?
Kill Bill has been successfully deployed in private data centers as well as in AWS, Heroku, OpenShift, Azure, etc. Our AWS deployments are offered at this Products page.


Does Kill Bill support recurring billing / usage billing / one-time billing?
Kill Bill supports recurring billing, usage billing, and one-time transactions. (See our Usage documentation to understand the various types of usage Kill Bill supports.)
How does Kill Bill handle payments?
Kill Bill is not a payment gateway. Instead, when a payment is triggered in Kill Bill, it connects to a payment gateway, which in turn handles the payment details and processing. (For more information on payments, see our Payment Guide.)
Connection to a payment gateway is achieved through plugins. We have some open-source payment plugins, but depending on your payment gateway, you may need to write your own plugin.
Need help developing a Kill Bill plugin? If your organization or development team needs help creating a plugin, we can recommend partners that have created them before for Kill Bill users. Check out one at Partners page.
What payment gateways can I use with Kill Bill?
Kill Bill is a generic platform to build billing and payment infrastructures. As such, it is agnostic of payment gateways.
Kill Bill communicates to payment gateways via plugins. Thus, there are virtually no restrictions on what payment gateway you can use. See our Payment Guide for more information.
What types of payment methods does Kill Bill support?
Kill Bill supports all the credit and debit cards your payment gateway supports. If your payment gateway supports ACH, then you can use Kill Bill to accept ACH, too!
Additionally, with Kill Bill, you can track external payments (such as checks, cash, and even Boleto Bancário). When you receive the money, simply let Kill Bill know about it (either via Kaui, our administrative UI or our APIs).
How does Kill Bill support international billing?
We designed the core of the billing platform to be internationalized. The catalog module has support for all currencies, including crypto-currencies (e.g. Bitcoin). The invoice module will understand these various currencies and respect localization rules. (For example, it will correctly round US dollars to two decimal places but Japanese Yen amounts will have no decimal portion.)
Accounts can have a designated locale (for example, $1,234.99 will be displayed as 1.234,99 $ for accounts with the French Canada locale) and a time zone (to generate invoices in their time zone instead of the merchant’s).
From a payment perspective, Kill Bill supports payment gateways via plugins. If your international gateway isn’t supported yet, you can simply write a plugin for it.
Note: If your organization or development team needs help writing a plugin, we can recommend partners that have created them before for Kill Bill users. Check out one at our Partners page.
Does Kill Bill include catalog functionality?

Kill Bill includes an XML catalog that supports these features (and more):

  • Real-time catalog with subscription plans and one-off products
  • Product tiers
  • Pricing lists
  • Different subscription types (main subscription, add-on subscriptions, etc.)
For more catalog information, see the Catalog section of our documentation.
If you have a very large catalog (e.g., thousands of products) and/or if it is highly dynamic, maintaining the catalog as an XML file may not be practical. Instead, you can use the CatalogPluginApi to write a plugin that would provide an alternative catalog implementation (such as integrating with your existing catalog system). See the documentation.
Here is a Java example.
Does Kill Bill support coupons and/or discounts?

There are several ways to handle coupons and discounts:

  • The simplest option is for your catalog to include discount plans (plans can additionally include discount phases)
  • An alternative is to use the PhasePriceOverride element when creating a subscription
  • Finally, to implement a fully fledged coupon functionality, use the EntitlementPluginApi to write your custom plugin (Kill Bill Coupon Plugin Demo is an example)

For more details, check this Moving Towards a Flexible Catalog post.

Can Kill Bill send my customers email notifications about payments that are due?

The email notifications plugin lets you send emails to your customers regarding upcoming invoices, payment successes and failures, subscription cancellations, etc.

Can Kill Bill accept cryptocurrency payments from my customers?
You can certainly do this; you’ll need to write a plugin to communicate with a payment gateway that supports different cryptocurrency coins (e.g., Bitcoin, Ethereum).
Note: If your organization or development team needs help writing a plugin, we can recommend partners that have created them before for Kill Bill users. Check out one at our Partners page.
What is a plugin?
A plugin is software written on top of the Kill Bill platform that interacts with the system. You would use a plugin to implement a specific feature or behavior that’s not part of the core Kill Bill system. See the Plugin Introduction.
Can Kill Bill send email notifications to customers about their account?
Yes, you can use the Email Notification plugin to send emails regarding late payments, failed payments, and other events that affect customers’ accounts.
Does Kill Bill work with multiple currencies?
Yes! To use multiple currencies, you would define each currency in the catalog. You would also define a currency for those customer accounts that don’t use the system’s default currency. For more advanced currency topics, see the Analytics Guide and Payment Control Plugin Guide.
Can I use Kill Bill to communicate with customers in their native language?
Kill Bill supports translations in the catalog, emails, and invoices. To read more about Kill Bill’s international features, including time zones and currencies, see the Internationalization Overview.
What kind of analytics can Kill Bill provide for my accountants and finance teams?
You can use the Analytics plugin to create reports and view them in real-time with Kaui. The plugin also supports the ability to create reports against external databases.

Compliance & Security

Is Kill Bill PCI compliant?
Even if Kill Bill is used in PCI compliant companies today, it is your responsibility to get certified. Depending on how you plan to use Kill Bill, you can outsource most of the PCI complexity to your payment gateway by not storing credit card information. Check the PCI DSS website for more information.
Is Kill Bill GDPR compliant?
By default, Kill Bill avoids storing any PII information. However, it is your responsibility to ensure that you remain GDPR compliant.
Does Kill Bill support taxes?
Kill Bill does not support taxes. Instead, we partner with Avalara to outsource tax compliance. Our AvaTax connector provides real-time and on-demand calculations to prevent overcharging or undercharging tax.
A free sandbox is available at Avalara, or you can contact us for an introduction. You can download the plugin Kill Bill Avatax.
How can I secure my Kill Bill installation?

Here are some general tips on securing your Kill Bill installation:

  • Install Kill Bill behind a firewall (it should not be exposed on the public internet).
  • Change the default username/password (admin/password) in your live environment.
  • Don’t store sensitive data in Kill Bill. While most plugins have support for directly saving card or bank account numbers, for instance, this should only be used for testing purposes or if you use a proxy tokenizer; if you don’t, use a third-party vault.
  • Encrypt username and passwords in configuration files.
  • Use SSL for all communication with your eCommerce application as well as with the payment providers.
  • Subscribe to our Community mailing list to receive security advisories.
  • Never store security codes (CCV, CVV, etc.) in your live environment.

It is eventually your responsibility to make sure your Kill Bill installation is secure and compliant.


Can I customize Kill Bill?

Yes—there are various ways to customize Kill Bill:

  • System properties—These let you configure the core platform. Also, most internal modules have a second, more advanced, layer of configuration, usually through XML files. These let you configure the dunning (overdue) policy, the various plans and billing policies, etc.
  • Plugins—If you need more advanced (billing or non-billing) logic, Kill Bill has a plugin capability. You can write custom code to extend or even override Kill Bill’s default behaviors. We can recommend development partners to help you do that, if necessary.
Can you develop customized Kill Bill logic or plugins for us?
The Kill Bill team does not develop customized logic or plugins. However, we have a partner who does that. In fact, they have successfully delivered many Kill Bill projects in the past for our clients, and they are very reasonably priced. You can find out more at Partners page.
Where is the code?
All of our code is hosted on Github, in the killbill organization. The core of the Kill Bill platform can be found on GitHub.

Getting Started

Where is the documentation?
Our documentation lives here: https://docs.killbill.io. We have documented our API here: https://killbill.github.io/slate.
How do I know that Kill Bill will work for my business?
If you want to know whether or not Kill Bill would work for your organization, we recommend that you perform a Proof of Concept (POC) against your business requirements. If you have questions about Kill Bill, please start by asking them in the Kill Bill Community (mailing list). We monitor the posts and can usually answer questions within a relatively short period of time. To install Kill Bill, look over the Getting Started tutorial. If you want to review the software code, it’s available on GitHub.
Can you help us get up and running with Kill Bill?
We have short-term consulting and ongoing support packages that can help. Check it out at Support page.
Is there a Kill Bill demo?
We have a self-directed demo that you can access at Kill Bill Demo. You can click around in Kaui, the administrative user interface for Kill Bill. If you’re interested in a high-level overview, see these two short videos on Kill Bill and Kaui.
How do I set up Kill Bill in my development environment?
I’ve tried to install Kill Bill and/or Kaui, but I got stuck. What should I do?
Make sure you’re familiar with the installation instructions in our documentation. If you’re sure that you’ve followed the steps correctly, you can post a description of your problem on the Kill Bill Community (mailing list). We monitor this list regularly and can usually help you get unstuck.
How do I get up to speed faster with Kill Bill?
To quickly get an idea of what Kill Bill is and its feature set, read What Is Kill Bill and watch our short overview video. Of course, our website is also a great reference to better understand Kill Bill.
You can then sign up for a self-driven demo. This is a read-only experience in Kaui, our back-office user interface, that demonstrates both Kaui’s and Kill Bill’s capabilities. (We have a short video that explains Kaui as well.)
Next, you can install Kill Bill and Kaui and get familiar with creating a tenant, account, catalog, subscriptions, and more, either via Kaui or API calls.
If you’re having trouble, make sure to double-check the documentation (guides and API). You can post your questions to the Kill Bill Community.

Technical FAQs

How stable are your APIs?

We have two release trains:

  • The latest release with an even minor number (e.g., 0.22.x) is stable (APIs are backward compatible).
  • The development team uses odd minor numbers for developing new features (0.17.x, 0.19.x, 0.21.x, etc.). API and DDL changes are frequent.
What kind of tests do you perform?

Before each release, there are thousands of tests that we perform:

  • Unit tests
  • Functional tests
  • Java library integration tests
  • Server integration tests to check the REST APIs
  • Client APIs integration tests

However, note that Kill Bill is a platform to build billing systems. There are many combinations of configurations possible, and we cannot test them all. We provide a test framework to help you verify your system before going to production.

Also, take extra care when installing third-party plugins.

Only the plugins hosted on our killbill organization on GitHub are officially supported.

We are not a Java shop. Can we still use Kill Bill?
Yes! We try to hide most of the complexity, so you can simply use Kill Bill as a service, using our client libraries. Currently, native plugins can only be written in Java. For other languages, we recommend writing a small shim to call remote services (e.g. Go application via gRPC).
What is a (subscription) bundle?
A bundle is a collection of subscriptions. A typical bundle has exactly one BASE subscription and a collection of ADD_ONs. Logically grouping these subscriptions makes it easier to automatically cancel all ADD_ONs when the BASE subscription is canceled, for example.
Can I create subscriptions without billing information?
Yes! If you are not ready to charge your customers (for example, during an activation phase), you can configure your plan with an initial free phase. Alternatively, you can set the AUTO_PAY_OFF tag on the customer account, and Kill Bill generates invoices but won’t attempt to charge them. When you decide to remove this tag, payments will automatically occur.
Can I create an account without a subscription?
Absolutely! Having an account without a subscription is useful during onboarding flows. For example, you may need your customer in your CRM engine, databases, and so forth before she has signed up.
What are the environment requirements?
Specifying definite environment requirements is tricky because it depends on the plugins you want to run, your expected traffic, etc. If in doubt, ask the Kill Bill Community (mailing-list). Remember to provide your details!
How can I listen to Kill Bill events?
You can either write a custom plugin (all Kill Bill events are visible to plugins) or register an endpoint that Kill Bill will send events to via HTTP POST (check our push notifications documentation).
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