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OpenCQRS Documentation

Welcome to the official documentation for OpenCQRS – an open-source application framework for building systems with CQRS and event sourcing on the JVM.

OpenCQRS is designed to work seamlessly with EventSourcingDB, making it straightforward to model, implement, and operate event-driven applications. Built with Java and Kotlin developers in mind, it provides ready-to-use building blocks for commands, events, aggregates, projections, and testing – all with a strong focus on clarity, testability, and maintainability.

OpenCQRS is developed and maintained by Digital Frontiers GmbH & Co. KG and released as open source software under the Apache 2.0 license. It is free to use and backed by professional expertise and consulting services when you need them.

Learning the Concepts

New to CQRS or event sourcing, or wondering how OpenCQRS can help you build applications? Start here:

  • Getting Started

    Step-by-step tutorials that guide you through building your first applications with OpenCQRS.

  • Guides and How-Tos

    Practical recipes for solving common problems and implementing specific features.

  • Reference

    Detailed reference documentation for commands, events, aggregates, projections, and the ESDB client SDK.

  • Concepts

    Background explanations of the core ideas behind OpenCQRS and its design principles.

Need a refresher on CQRS or Event Sourcing?

If you are new to the underlying concepts, visit CQRS.com for an in-depth introduction to CQRS and event sourcing.

Platform and Integration

OpenCQRS runs on the Java Virtual Machine and is fully compatible with JVM-based languages such as Java and Kotlin. It integrates seamlessly into modern application stacks:

  • Available from Maven Central for both Maven and Gradle builds
  • Smooth integration with Spring Boot for rapid application development and production deployment
  • Native support for EventSourcingDB as the underlying event store, with a dedicated Java client SDK
  • Built-in support for testing command logic with fixtures and utilities
  • Modular architecture for extension and customization

Need Support?

If you or your team need help designing, integrating, or scaling applications with OpenCQRS, the team behind the framework is here to assist. Just reach out at opencqrs@digitalfrontiers.de.