Cratis Arc C# host selection

Cratis Arc offers two C# HTTP hosts: ASP.NET Core through Cratis.Arc, or a lightweight HttpListener host through Cratis.Arc.Core. Choose the host before following a setup guide: both use Arc.Core’s command and query model, but their startup code is different. Persistence and TypeScript proxy generation are separate choices; neither host requires Cratis 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 want a small HTTP service using .NET’s HttpListener, without ASP.NET Core middleware or controllers

For an ASP.NET Core application, start with the standalone getting-started path. If you choose the lightweight host, follow the Arc.Core getting-started guide instead. Use the complete startup example for your chosen host: the builders and extension methods are host-specific.

Using Arc.Core without ASP.NET Core does not establish compatibility with every device, desktop, browser, ahead-of-time (AOT) compilation target, or restricted runtime. Check the selected host and dependencies on your deployment target before choosing it.

Then choose persistence and client output

Once you have chosen a host, decide how each command saves changes. Commands may call application services, write MongoDB collections, or use EF Core contexts. Add Chronicle explicitly when a feature needs event persistence, projections that build read models from events, or reactors that respond to events. Returning an event-shaped object from standalone Core is ordinary response handling, not an automatic append to an event log.

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.

If you want generated TypeScript clients, configure proxy generation after choosing the host. The generator is a separate post-build tool: install its build package and configure an output path. It inspects compiled assemblies and uses PDB debug information for source-file grouping, so the backend does not need to be running. Generate in Debug before type-checking the frontend.

Continue

• Set up Arc with ASP.NET Core — 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.