Backend hosting overview

You want one command/query model without accidentally choosing an event store or the wrong web host. Arc separates those decisions: Arc.Core provides the application model, and Cratis.Arc adds ASP.NET Core integration. Neither requires Chronicle.

Choose the host first

Host	Package and bootstrap	Use it when…
ASP.NET Core	Cratis.Arc, WebApplication.CreateBuilder(args), builder.AddCratisArc(), app.UseCratisArc()	You want ASP.NET Core routing, middleware, controllers alongside model-bound endpoints, and its authentication ecosystem
Lightweight host	Cratis.Arc.Core, ArcApplication.CreateBuilder(args)	You intentionally want Arc’s generic-host / HttpListener-based endpoint surface without ASP.NET Core

The standalone getting-started path uses ASP.NET Core throughout. The Arc.Core getting-started guide explains the alternative. Do not copy one host’s extension-method sequence into the other.

Arc.Core is useful when you do not need ASP.NET Core, but that is not a guarantee of compatibility with every device, desktop, browser, AOT, or restricted runtime. Validate the selected host and dependencies on your deployment target.

Then choose persistence and client output

Commands may call application services, write MongoDB collections, or use EF Core contexts. Add Chronicle explicitly when the slice needs event persistence, projections, or reactors. Returning an event-shaped object from standalone Core is ordinary response handling, not an automatic append.

Separate decisions from inline persistence

Direct service and database calls remain supported. When a model-bound command can describe its writes from the available inputs, prefer a pure Handle() returning command operations. Chronicle commands should still return events for durable facts; operations do not replace queries or Provide() reads.

Proxy generation is a separate post-build tool. Install its build package and configure an output path; it inspects compiled assemblies and PDB source information rather than querying your running endpoints. Generate in Debug before type-checking the frontend.

Continue

• Set up standalone Arc — packages, imports, database configuration, and the first runnable checkpoint.
• ASP.NET Core integration — middleware, authentication, and host-specific behavior.
• Arc.Core overview — the lightweight surface and its limits.
• Backend guide — commands, queries, providers, identity, and tenancy.