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FactStore - Official Documentation

A lightweight, Kotlin-first event store designed for clarity, correctness, and extensibility — built on a clean specification and powered by FoundationDB. 🚀

What is FactStore?​

The FactStore project is a collection of libraries to build flexible event-sourced applications, including a specification for event sourcing and event streaming, as well as a backing implementation of that specification powered by FoundationDB.

Subproject: factstore-specification​

This subproject defines the core contracts and behavioral rules for a FactStore implementation. It is written in Kotlin and establishes the APIs for:

  • Appending events (also called facts)
  • Reading streams of facts
  • Subscribing to live or historical streams
  • Managing event ordering and consistency guarantees

This module is intentionally implementation-agnostic, serving as the foundation for any backend.

Other subprojects include:

  • FactExplorer: A UI tool to explore and manage fact stores.

Subproject: factstore-foundationdb​

An implementation of the specification using FoundationDB as the storage engine. This module provides:

  • A stateless event-sourcing layer built on FoundationDB’s transactional model
  • Strong consistency and ordered event writes
  • Efficient range reads and streams
  • A clean separation between domain logic and storage mechanics

If you want a production-ready FactStore backed by FoundationDB, this is the module for you.