diff --git a/conftest.py b/conftest.py
new file mode 100644
index 0000000..88fe65b
--- /dev/null
+++ b/conftest.py
@@ -0,0 +1,11 @@
+from pytest import Config
+
+
+def pytest_configure(config: Config):
+    """
+    Registers a new mark 'final' that can be applied to tests.
+
+    I did not want to add these in pyproject.toml.
+    """
+
+    config.addinivalue_line("markers", "final: the final test")
diff --git a/pyproject.toml b/pyproject.toml
index d4c43ed..c0b2f35 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -64,6 +64,7 @@ omit = ["tests.py"]
 source_dirs = ["src/"]
 
 [tool.pytest]
+# custom marks are created in conftest.py
 asyncio_mode = "auto"
 
 [tool.ruff]