# What an Atrium app is

Atrium app developer spec, section 1: What an Atrium app is.

An Atrium app is an **HTTPS service you run** (yourself, or later on Atrium Hosting). COHO never contains your business logic.

```text
Manager connects the app in the Store
  -> COHO POSTs signed lifecycle.setup to you
  -> you store the API key + signing secret
  -> COHO may POST signed events/schedules
  -> you call Public API v1.1 with the API key
  -> you write Store logs
  -> optional: COHO loads your quick view URL in an iframe
```

Same runtime contract for COHO-built apps, private org URL apps, and (later) Partners.