diff --git a/extras.json b/extras.json
deleted file mode 100644
index 35033643..00000000
--- a/extras.json
+++ /dev/null
@@ -1 +0,0 @@
-{"diptest": ["diptest"]}
\ No newline at end of file
diff --git a/popmon/extensions/extension.py b/popmon/extensions/extension.py
index 7c8695b2..ad53218d 100644
--- a/popmon/extensions/extension.py
+++ b/popmon/extensions/extension.py
@@ -19,14 +19,8 @@
 from __future__ import annotations
 
 import importlib.util
-from pathlib import Path
 from typing import Callable
 
-try:
-    import tomllib
-except ModuleNotFoundError:
-    import tomli as tomllib
-
 
 def is_installed(package):
     is_present = importlib.util.find_spec(package)
@@ -36,19 +30,8 @@ def is_installed(package):
 class Extension:
     name: str
     extension: Callable
-
-    @property
-    def requirements(self):
-        pyproject_path = Path(__file__).parent.parent.parent / "pyproject.toml"
-        with pyproject_path.open("rb") as f:
-            data = tomllib.load(f)
-
-        project = data["project"]
-        extras = project.get("optional-dependencies", {})
-        if self.name not in extras:
-            return []
-
-        return extras[self.name]
+    # should also be added to `pyproject.toml` optional-dependencies
+    requirements: list[str]
 
     def check(self):
         if all(is_installed(package) for package in self.requirements):
diff --git a/popmon/extensions/profile_diptest.py b/popmon/extensions/profile_diptest.py
index 92118655..21b597c3 100644
--- a/popmon/extensions/profile_diptest.py
+++ b/popmon/extensions/profile_diptest.py
@@ -68,3 +68,4 @@ def diptest_profile(bin_centers, bin_values, bin_width, rng=None):
 class Diptest(Extension):
     name = "diptest"
     extension = extension
+    requirements = ["diptest"]
diff --git a/pyproject.toml b/pyproject.toml
index 9de7ffd4..61b0083b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -32,8 +32,7 @@ dependencies = [
     "joblib>=0.14.0",
     "htmlmin",
     "pydantic",
-    "typing_extensions",
-    "tomli >= 1.1.0 ; python_version < '3.11'"
+    "typing_extensions"
 ]
 classifiers = [
     "Programming Language :: Python :: 3",