diff --git a/src/kit.ts b/src/kit.ts
index 97990002..d1999a15 100644
--- a/src/kit.ts
+++ b/src/kit.ts
@@ -14,6 +14,7 @@ import {
 } from "three";
 import { GLTFLoader } from "three/addons/loaders/GLTFLoader.js";
 import type { Placement } from "./generator";
+import { collectionChildCount } from "./kitNames";
 
 function tex(loader: TextureLoader, url: string, srgb = false): Texture {
   const t = loader.load(url);
@@ -131,8 +132,7 @@ export class Kit {
   }
 
   count(collection: string): number {
-    const c = this.manifest.collections[collection];
-    return c?.children?.length || 1;
+    return collectionChildCount(this.manifest, collection);
   }
 
   /** Set the floor emissive intensity on BOTH the exterior floor material and its
diff --git a/src/kitNames.ts b/src/kitNames.ts
new file mode 100644
index 00000000..a297194a
--- /dev/null
+++ b/src/kitNames.ts
@@ -0,0 +1,49 @@
+/**
+ * Placement keys are `COL[collection][index]` / `OBJ[name]`. Kit.count used to
+ * return 1 for a missing collection (`|| 1`), so a typo'd mesh name compiled to
+ * `COL[typo][0]` and vanished at instance time with only a console warning.
+ */
+
+export interface KitNameCollection {
+  children?: { index: number; kind: string; name: string }[];
+  missing?: boolean;
+}
+
+export interface KitNameManifest {
+  collections: Record<string, KitNameCollection>;
+  objects: Record<string, unknown>;
+}
+
+const COL_KEY = /^COL\[(.+)\]\[(\d+)\]$/;
+const OBJ_KEY = /^OBJ\[(.+)\]$/;
+
+export function collectionChildCount(manifest: KitNameManifest, name: string): number {
+  const c = manifest.collections[name];
+  const n = c?.children?.length ?? 0;
+  if (!c || c.missing || n === 0) {
+    throw new Error(`kit: unknown or empty collection ${JSON.stringify(name)}`);
+  }
+  return n;
+}
+
+export function assertKnownPlacementKey(key: string, manifest: KitNameManifest): void {
+  const col = key.match(COL_KEY);
+  if (col) {
+    const n = collectionChildCount(manifest, col[1]);
+    const idx = Number(col[2]);
+    if (!Number.isInteger(idx) || idx < 0 || idx >= n) {
+      throw new Error(
+        `kit: index ${idx} out of range for collection ${JSON.stringify(col[1])} (n=${n})`,
+      );
+    }
+    return;
+  }
+  const obj = key.match(OBJ_KEY);
+  if (obj) {
+    if (!(obj[1] in manifest.objects)) {
+      throw new Error(`kit: unknown object ${JSON.stringify(obj[1])}`);
+    }
+    return;
+  }
+  throw new Error(`kit: malformed placement key ${JSON.stringify(key)}`);
+}
diff --git a/tools/kitNames.test.ts b/tools/kitNames.test.ts
new file mode 100644
index 00000000..ed922dbe
--- /dev/null
+++ b/tools/kitNames.test.ts
@@ -0,0 +1,54 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { readFileSync } from "node:fs";
+import { assertKnownPlacementKey, collectionChildCount } from "../src/kitNames";
+import type { KitNameManifest } from "../src/kitNames";
+
+const manifest = JSON.parse(
+  readFileSync(new URL("../public/assets/kit_manifest.json", import.meta.url), "utf8"),
+) as KitNameManifest;
+const generatorSrc = readFileSync(new URL("../src/generator.ts", import.meta.url), "utf8");
+
+test("collectionChildCount throws on a typo'd mesh name (the old || 1 hole)", () => {
+  assert.throws(
+    () => collectionChildCount(manifest, "ground side wall"),
+    /unknown or empty collection "ground side wall"/,
+  );
+});
+
+test("collectionChildCount accepts live Blender collection names", () => {
+  assert.equal(collectionChildCount(manifest, "groud side wall"), 1);
+  assert.ok(collectionChildCount(manifest, "wall.001") > 1);
+});
+
+test("every COL() / OBJ() name in generator.ts exists in kit_manifest.json", () => {
+  const cols = new Set(
+    [...generatorSrc.matchAll(/COL\(\s*"([^"]+)"/g)].map((m) => m[1]),
+  );
+  for (const m of generatorSrc.matchAll(/`COL\[([^\]]+)\]\[/g)) {
+    if (!m[1].includes("${")) cols.add(m[1]);
+  }
+  const objs = new Set(
+    [...generatorSrc.matchAll(/OBJ\(\s*"([^"]+)"/g)].map((m) => m[1]),
+  );
+  const missingCols = [...cols].filter((n) => {
+    try {
+      collectionChildCount(manifest, n);
+      return false;
+    } catch {
+      return true;
+    }
+  });
+  const missingObjs = [...objs].filter((n) => !(n in manifest.objects));
+  assert.deepEqual(missingCols, []);
+  assert.deepEqual(missingObjs, []);
+});
+
+test("assertKnownPlacementKey pin: in-range COL and known OBJ pass; OOB / unknown fail", () => {
+  assertKnownPlacementKey("COL[wall.001][0]", manifest);
+  assertKnownPlacementKey("OBJ[store_roof]", manifest);
+  assert.throws(() => assertKnownPlacementKey("COL[wall.001][99999]", manifest), /out of range/);
+  assert.throws(() => assertKnownPlacementKey("COL[not-a-mesh][0]", manifest), /unknown or empty/);
+  assert.throws(() => assertKnownPlacementKey("OBJ[nope]", manifest), /unknown object/);
+  assert.throws(() => assertKnownPlacementKey("lights.001", manifest), /malformed/);
+});