This spec, the signature test vectors (§3.1.1), and the four hello-world samples are the official Atrium connecting kit. There is no npm / NuGet / PyPI SDK package — by design. Copy a hello, keep the signature verify + lifecycle paths, delete what you do not need. Public snapshot: CompanyForLife/atrium-app-samples.
| Sample | Class | Language |
|---|---|---|
samples/hello-node (atrium-app-samples) |
Web app (default) | Node 20+ |
samples/hello-dotnet (atrium-app-samples) |
Web app (default) | .NET minimal API |
samples/hello-python (atrium-app-samples) |
Web app (default) | Python 3, standard library only |
samples/hello-go (atrium-app-samples) |
Web app (default) | Go, standard library only |
samples/hello-agent-node (atrium-app-samples) |
Agent (exception) | Node 20+ |
The four language hellos implement the same web app surface: health, signed lifecycle webhooks, signed triggers, native config routes with a schema from §5.3.1, optional disk persistence (ATRIUM_DATA_DIR), quick view (/ui), external configure (/configure), and Public API capability probes in the quick view.
hello-agent-node is the only starter without a UI. Use it only for true background agents (§6). Its README states that explicitly — copy a web-app hello unless you have a written reason not to.
We deliberately do not publish a language package. The runtime contract is a few hundred lines in any language, most of which is HTTP routing you already have in your own stack, and a library that owns your server is useless if you are adding Atrium to an existing app. Verifying signatures is the one part where a subtle mistake is a security hole rather than a bug, which is why it has published test vectors instead of a package.
Start from a hello sample. Richer demo apps (schedules, persistence beyond the sample state file, real product workflows) may exist for COHO dogfooding; they are not part of the supported external starter set. In-repo kits/atrium-node is birthday-dogfood only and not a supported partner interface.
Samples target self-host by default. If COHO runs your image on Atrium Hosting, follow the Dockerfile contract in §5.6; if your source lives in a private repository, see §5.5.