---
title: Integrate with Chronicle
description: Add Chronicle's event-sourced write path to an Arc application while keeping Arc's commands, queries, identity, tenancy, and generated proxies.
---


`Cratis.Arc.Chronicle` is the integration package that extends Arc with [Cratis Chronicle](https://github.com/Cratis/Chronicle) capabilities. It wires the two frameworks together so that Arc's application model — commands, queries, identity, tenancy, and code generation — works seamlessly with Chronicle's event sourcing infrastructure.

Arc does not require Chronicle, and Chronicle does not require Arc. That independence is useful for adoption and bounded current-state slices. In a full Cratis information system, though, this integration is the natural pairing: Arc gives the CQRS boundary and Chronicle keeps the event-sourced facts underneath it.

## What it provides

Without this package, Arc and Chronicle are independent. With it:

- **Commands return events** — `Handle()` methods on commands can return event records directly; the package appends them to the correct event log automatically.
- **Event source resolution** — the command context (current user identity, tenant, route parameters) is used to resolve the event source id without manual plumbing.
- **Read models backed by projections** — Arc's read model conventions drive Chronicle projections so that query responses always reflect the current projected state.
- **Tenant-aware event stores** — each tenant's event log and projections are namespaced automatically, matching Arc's tenancy model.
- **Compliance integration** — PII-annotated properties are decrypted transparently before read models are served, and the compliance subject is set on commands from the current identity.
- **Aggregate support** — aggregate roots are discoverable and invocable via the standard command pipeline, with Chronicle managing the event stream and rehydration.
- **Validation with read models** — domain constraint checks can read current projected state directly inside `Handle()` without an extra query round-trip.

## Topics

| Topic | Description |
| ----- | ----------- |
| [Aggregates](/arc/backend/chronicle/aggregates/) | Working with aggregate roots and event sourcing. |
| [Add event sourcing to an Arc slice](/arc/backend/chronicle/add-event-sourcing/) | Move one database-backed slice to Chronicle while keeping its query and React screen in place. |
| [Cratis Package](/arc/backend/chronicle/cratis-package/) | The convenience package for Arc + Chronicle applications. |
| [React to an event](/arc/backend/chronicle/react-to-an-event/) | Run side effects or follow-up commands from Chronicle events with reactors. |
| [Commands](/arc/backend/chronicle/commands/) | Returning events from commands, event source id resolution, and concurrency scoping. |
| [Resolving EventSourceId](/arc/backend/chronicle/resolving-event-source-id/) | How Chronicle resolves aggregate and read model identity from commands and query arguments. |
| [Read Models](/arc/backend/chronicle/read-models/) | How read models are hooked up to Chronicle projections. |
| [Tenancy](/arc/backend/chronicle/tenancy/) | Tenant-aware namespaces for event stores and projections. |
| [Validation](/arc/backend/chronicle/validation/) | Validation with read models and identity resolution conventions. |
| [Compliance](/arc/backend/chronicle/compliance/) | PII decryption on read models and compliance subject resolution on commands. |
| [Code Analysis](/arc/backend/chronicle/code-analysis/) | Diagnostics and analyzers specific to the Chronicle integration. |