diff --git a/README.md b/README.md
index 363caca..acfe86e 100644
--- a/README.md
+++ b/README.md
@@ -21,8 +21,41 @@ The API is split in two layers:
   (`/api/software*`, `/api/builds*`, `/api/image`, `/api/download`, `/file/*`)
   and the catalog ActiveAdmin resources. See its [README](libs/ruby/warp_engine/README.md).
 - **The host app** (`apps/api`) owns everything TTG-specific: members, events,
-  wiki proxy, RSS feeds, Devise/ActiveAdmin authentication, theming and assets.
-  It consumes WarpEngine as a path gem and mounts it at `/`.
+  the store registry, wiki proxy, RSS feeds, Devise/ActiveAdmin authentication,
+  theming and assets. It consumes WarpEngine as a path gem and mounts it at `/`.
+
+## The store registry
+
+`GET /api/stores` lists the stores a client can install from. The desktop
+graphical client reads it on first run, which is why it is **public**: a client has
+nobody to log in as.
+
+```json
+[
+  {
+    "name": "Teletype Games",
+    "catalogUrl": "https://teletypegames.org",
+    "storeRepositoryUrl": "https://git.teletypegames.org/stores/ttg-desktop-store"
+  }
+]
+```
+
+A `Store` row is three fields — `name`, `catalog_url`, `store_repository_url` —
+maintained from **ActiveAdmin ▸ 🛒 Stores**, and `db/seeds.rb` creates our own.
+The client derives everything else: it reads `config.json` from the store
+repository, points it at `catalog_url`, and falls back to the engine's defaults if
+that repository has no config file.
+
+This lives in the host app **on purpose, not in WarpEngine**. The engine serves
+one catalog and has no business knowing which stores exist for it; who ships a
+store for a catalog is a property of the site.
+
+| | |
+|---|---|
+| Model | `apps/api/app/models/store.rb` |
+| Endpoint | `apps/api/app/controllers/api/stores_controller.rb` |
+| Admin | `apps/api/app/admin/stores.rb` |
+| Client | [`warp-engine-desktop-gui`](https://git.teletypegames.org/stores/warp-engine-desktop-gui) |
 
 ## Development environment