diff --git a/Documentation/FAC.md b/Documentation/FAC.md
index 74d3530..ba56263 100644
--- a/Documentation/FAC.md
+++ b/Documentation/FAC.md
@@ -286,6 +286,28 @@ docker login gitea.mysuperlab.netcraze.pro
 
 ---
 
+## Tests
+
+```powershell
+npm test                                                # whole suite
+node --test server/__tests__/floor-brightness.test.js   # one file
+```
+
+Runs `node --test server/__tests__/**/*.test.js` — **15 suites, 41 tests, ~1 s**. No test framework is installed: this is Node's built-in runner, and `node --test` expands the `**` pattern itself, so the command behaves the same from PowerShell, cmd and bash.
+
+The suite needs **no database and no running server** — the tests read the client's style and geometry modules from disk and call the server's validators directly.
+
+| Area | Test files |
+|---|---|
+| Hang geometry and clearance | `painting-column-clearance`, `doorway-clearance` |
+| Period interiors | `abex-loft-interior`, `baroque-panels`, `dada-interior`, `high-renaissance-interior`, `mannerist-columns`, `neoclassical-interior`, `surrealist-interior` |
+| Brightness and windows | `floor-brightness`, `no-factory-windows` |
+| Movement links and lineage | `movement-lineage-service` |
+
+**Write the test before the code it covers** — see [Bible.md](Bible.md). The interior rules this suite enforces are described in [data-and-images.md](data-and-images.md).
+
+---
+
 ## Build frontend
 
 ```powershell
diff --git a/Documentation/data-and-images.md b/Documentation/data-and-images.md
index 040f2ec..1258ac4 100644
--- a/Documentation/data-and-images.md
+++ b/Documentation/data-and-images.md
@@ -326,6 +326,8 @@ Wing layout lives in `client/src/utils/movementHallLayout.ts` (up to 55 works pe
 
 **Paintings must not sit in front of mid-wall bay columns/pilasters.** Column Z centres use the same `bayPositions` formula as the period modules. Keep-out half-widths per `details` kind live in `client/src/utils/sideColumnKeepOuts.ts` (`SIDE_WALL_COLUMN_RHYTHMS`: gothic, roman, quattrocento, cinquecento, mannerist, neoclassical, gothic-revival, art-nouveau). Side-wall hang packs into the gaps between those keep-outs and **grows hall depth** when needed; columns are never moved. Windows also treat column keep-outs as occupied so they do not land on shafts. Regression: `server/__tests__/painting-column-clearance.test.js`.
 
+Run `npm test` after touching any interior module, hall layout or tint: the rules above are covered by 15 suites under `server/__tests__/` that parse these source files directly — see [FAC.md](FAC.md) § Tests.
+
 The same U-hang applies to artist halls and guided tours (artist halls have no period bay columns). Hall lighting is **shared** (no per-painting spotlights) so `MeshStandardMaterial` walls stay within WebGL light limits — see [basics.md](basics.md) § Shared 3D behaviour. To change a movement’s look, edit its entry in `movement-interior-styles.ts` and rebuild the client.
 
 ## Historical event markers (frontend timeline)
diff --git a/Documentation/setup.md b/Documentation/setup.md
index 1d2fa9b..2d5fe47 100644
--- a/Documentation/setup.md
+++ b/Documentation/setup.md
@@ -2,7 +2,7 @@
 
 ## Prerequisites
 
-- **Node.js** 20+
+- **Node.js** 20+ (verified on 24.19; `npm test` relies on `node --test` expanding `**` itself, which older majors may not do)
 - **PostgreSQL** reachable from the app host
 - Network access to Wikipedia / Wikimedia (for biographies, seeding, and on-demand image fetch)
 
@@ -107,6 +107,7 @@ Image fetch can take hours if you run it for the entire catalog. The first line
 
 | Command | Purpose |
 |---------|---------|
+| `npm test` | **Test suite** — 15 suites / 41 tests on Node’s built-in runner; no database or server needed |
 | `npm run dev:web` | **Public dev stack** — Vite `:5173`, API `:3451` (Keenetic → devgallery…) |
 | `npm run prod:docker:publish` | Build + push prod image to Gitea |
 | `npm run devtoprod:images` | Copy `data/images/` → TrueNAS via SMB `Gallery` share |
diff --git a/README.md b/README.md
index 05c8c8c..da1a4dc 100644
--- a/README.md
+++ b/README.md
@@ -86,6 +86,14 @@ Operator guide: [Documentation/environments.md](Documentation/environments.md).
 npm run dev:web   # Vite :5173, API :3451
 ```
 
+**Tests** (Node’s built-in runner — no database or server needed):
+
+```bash
+npm test   # 15 suites, 41 tests
+```
+
+Per [Documentation/Bible.md](Documentation/Bible.md), write the test before the code it covers.
+
 **Local HMR:**
 
 ```bash