diff --git a/AGENTS.md b/AGENTS.md
index de5c2753..6579f6db 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -31,6 +31,34 @@ ask first.**
 
 Writing to *another* repository is not an exception either. Do it only when told to work there.
 
+### Do not add top-level files or folders
+
+**Never add a new directory or file at the repository root on your own.** The root layout is the
+maintainer's. Work belongs inside an existing module or directory — Python under `api/`, the client
+under `app/`, documents under `docs/<topic>/`, CI under `.github/`, developer scripts under `tools/`,
+temporary files under the git-ignored `.tmp/`. If a new top-level entry seems necessary, propose it
+(what, why, and which existing directories you ruled out) and wait for approval; then add it to the
+list below in the same change.
+
+Approved tracked root entries (`api/tests/test_repo_layout.py` fails on anything else):
+
+| Entry | Purpose |
+|---|---|
+| `api/`, `app/` | The model-serving API (Python) and the client (Kotlin) |
+| `docs/` | Documents and the GitHub Pages guide |
+| `tools/` | Developer tooling (release sync, web bundle sync) |
+| `benchmarks/` | Measurement scripts |
+| `script/` | Desktop UI driving script for the native-image build (`script/drive-desktop.ps1`) |
+| `gradle/`, `build.gradle.kts`, `settings.gradle.kts`, `gradle.properties`, `gradlew`, `gradlew.bat` | Gradle build |
+| `pyproject.toml` | Python project (uv) |
+| `.github/` | CI workflows |
+| `.idea/` | Shared IDE settings (partly tracked) |
+| `README.md`, `AGENTS.md`, `PROJECT.md`, `LICENSE.md` | Root documents |
+| `.gitignore`, `.gitattributes`, `.env.example` | Git and environment templates |
+
+Local, git-ignored entries that tools create are fine: `.tmp/`, `.worktrees/`, `.venv/`, `.gradle/`,
+`.kotlin/`, `.env`, `local.properties`, `uv.lock`, `.claude/`, `.DS_Store`.
+
 ## 3. Worktrees link large artefacts instead of copying them
 
 A worktree is a full checkout. Copying large untracked artefacts (prebuilt runtimes, vendored trees,
diff --git a/api/tests/test_repo_layout.py b/api/tests/test_repo_layout.py
new file mode 100644
index 00000000..123852aa
--- /dev/null
+++ b/api/tests/test_repo_layout.py
@@ -0,0 +1,40 @@
+"""
+The repository root holds only the entries AGENTS.md §2 approves; anything else is a new top-level
+file or folder that was added without approval.
+"""
+import re
+import subprocess
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[2]
+
+
+def approved_entries():
+    agents = (ROOT / "AGENTS.md").read_text(encoding="utf-8")
+    table = agents.split("Approved tracked root entries", 1)[1].split("\n\n", 2)[1]
+    entries = set()
+    for row in table.splitlines()[2:]:  # skip the header and the separator
+        first_cell = row.split("|")[1]
+        entries.update(name.rstrip("/") for name in re.findall(r"`([^`]+)`", first_cell))
+    return entries
+
+
+def tracked_root_entries():
+    names = subprocess.run(
+        ["git", "ls-files"], cwd=ROOT, capture_output=True, text=True, check=True
+    ).stdout.splitlines()
+    return {name.split("/", 1)[0] for name in names}
+
+
+def test_every_tracked_root_entry_is_approved():
+    unapproved = tracked_root_entries() - approved_entries()
+
+    assert unapproved == set(), (
+        f"top-level entries not approved in AGENTS.md §2: {sorted(unapproved)} "
+        "— propose them and add them to the list, or move the work into an existing directory"
+    )
+
+
+def test_the_approved_list_is_read():
+    assert {"api", "app", "docs", "AGENTS.md", "pyproject.toml"} <= approved_entries()