Kaui

Kaui, the Open Source Billing Admin UI

Kaui is the free, open source admin UI of Kill Bill. Support, finance, operations and product teams use it to manage accounts, subscriptions, invoices, payments and tenants without calling the API.

Last updated: October 2026

Download Kill Bill and Kaui

Read the Kaui Guide

Short answer

What is Kaui?

Kaui (Kill Bill Admin User Interface) is the open source web admin UI of Kill Bill, free under the Apache 2.0 license. It talks to Kill Bill over HTTPS and uses the same users, roles and permissions. Support and finance teams use it to manage accounts, subscriptions, invoices, payments, refunds, credits and chargebacks. Administrators use it to configure tenants, upload catalogs, set overdue flows, manage users and install plugins.

License: Apache 2.0, free
Built with: Ruby on Rails engines, which you can extend with your own
Runs as: The killbill/kaui Docker image or a WAR file
DockerTomcat
Quick start: Port 9090, user admin, password password
Source: GitHub
Guide: Kaui Guide

Users & Permissions

Manage back-office users, roles and permissions, with the same rules as the Kill Bill API.

Subscriptions

Add, change, pause, resume and cancel subscriptions, add add-ons and change the billing cycle day.

Customer Service Tasks

Check balances, add credits and charges, refund payments and record chargebacks.

Advanced Search

Find accounts, invoices, payments, subscriptions and other Kill Bill objects.

Custom Metadata

Label and organize objects with tags and custom fields.

Reports

View and configure reports with the analytics plugin, and create your own.

System Management

Configure tenants, upload catalogs, set overdue flows and install plugins.

Audit and History Tracking

A timeline of the events on each account, and audit logs of what changed.

Screenshots

Kaui in Four Screens

Kaui account page for a demo customer: account information, balance, bill cycle day, next invoice date and overdue status — **Account.** Balance, credit, bill cycle day, next invoice date and overdue status in one place.

Kaui invoice for a plan upgrade: Growth monthly 173.32 USD, an adjustment of minus 42.68 USD, total 130.64 USD — **Invoice.** A plan upgrade with proration: the new plan charged, the old plan credited.

Kaui subscription bundle: a Growth monthly base subscription in its evergreen phase, with start date, charged-through date and quantity — **Subscriptions.** Each bundle with its plan, phase and dates, plus advanced search.

Kaui analytics: the Daily New Subs report over the last three months — **Reports.** Analytics plugin reports, such as daily new subscriptions.

Who Uses Kaui

What Each Team Does in Kaui

Team	In Kaui
Customer support	Find an account, change or cancel a subscription, add a credit, refund a payment
Finance	Pay, void or write off invoices, record chargebacks and external payments, view reports
Operations and admins	Configure tenants, upload the catalog, set overdue flows, manage users and roles, install plugins
Developers and QA	Test flows, generate dry-run invoices, add test payment methods, read the account timeline
Product managers	Check plans and prices, follow subscriptions, read reports

Kaui and Aviate

Kaui or Aviate?

Kaui comes free with Kill Bill. Aviate, the enterprise offering of Kill Bill, has its own interface with more features.

	Kaui	Aviate
Accounts, subscriptions, invoices, payments	Yes	Yes
Catalog	Upload an XML catalog or create simple plans	A catalog editor for plans, phases and prices
Coupons, prepaid credits, metering	Through custom plugins	Aviate Coupons, Aviate Wallet, Aviate Metering
Tax	AvaTax plugin screens	Aviate Tax: rates per country and per product
Operations	Tenants, users, plugins, reports	Adds Aviate Health
Support	Community, no SLA	Level 3 support from the engineers
Cost	Free	A fixed annual fee, never a share of revenue. Pricing

Aviate Billing Operations Without Engineering How billing, support and finance teams investigate invoices, resolve unpaid invoices and audit account history in Kill Bill, with Kaui and Aviate. Kill Bill vs Aviate: Open Source or Enterprise Kill Bill is free, open source billing. Aviate runs on it and adds the Control Plane, modules and direct support from the engineers. Compare them. Download Kill Bill: Free, Open Source Billing Software Download Kill Bill, the free, open source billing platform: run it with Docker in a few minutes, in Tomcat or on Kubernetes, or try the Aviate sandbox. What's New in Kill Bill and Aviate, 2026 Latest Kill Bill, Kaui and Aviate releases, with dates: 34 releases in 2026 so far, new Aviate features, Insider Preview modules and the MCP server.

FAQs

Kaui FAQ

What is Kaui?

Kaui (Kill Bill Admin User Interface) is the open source web admin UI of Kill Bill. Support, finance and operations teams use it to manage accounts, subscriptions, invoices and payments, and administrators use it to configure tenants, catalogs, users and plugins.

Is Kaui free?

Yes. Kaui is open source under the Apache 2.0 license, like Kill Bill. The open source version comes without support or SLA.

How do I install Kaui?

The Docker quick start on the Download page starts Kill Bill, Kaui and a MariaDB database with one docker-compose.yml file. Kaui then answers on port 9090. You can also deploy the Kaui WAR file from Maven Central in Tomcat.

What is the default Kaui login?

After the Docker quick start, log in with the user admin and the password password. Change it before any shared use.

Can I refund a payment in Kaui?

Yes. Open the payment details and refund all or part of the payment. You can also record a chargeback from the same page.

Can I control who does what in Kaui?

Yes. Kaui uses the Kill Bill users, roles and permissions, so a support agent can see accounts without being able to refund, for example. Users can come from the Kill Bill database, LDAP or Active Directory, Okta or Auth0.

Can I change the catalog in Kaui?

Kaui lets you upload an XML catalog, create simple plans, view the catalog as XML and download it. Aviate adds a catalog editor to create and change plans, phases and prices without editing XML.

Can I extend Kaui?

Yes. Kaui is built as Ruby on Rails engines, so you can mount your own engine, for example to add screens for your own plugin.

What is the difference between Kaui and Aviate?

Kaui is the free, open source admin UI of Kill Bill. Aviate, the enterprise offering of Kill Bill, has its own interface and adds a catalog editor, coupons, prepaid credits, metering, tax rates per country and health monitoring, plus Level 3 support, for a fixed annual fee.