diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 9ac22d4ca..c1dcf7739 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -257,7 +257,7 @@ We use [pytest](https://docs.pytest.org) to run our tests and
 [pytest-cov](https://pytest-cov.readthedocs.io) to compute coverage.
 
 *   While developing, periodically check that changes do not break anything. For fast checks, use
-    `pytest -c dev_tools/conf/pytest.ini PATH`, where `PATH` is a directory or pytest file to test.
+    `pytest -m "not slow" PATH`, where `PATH` is a directory or pytest file to test.
 
 *   After finishing a task, run `check/pytest` to test all of the OpenFermion code.
 
diff --git a/check/pytest b/check/pytest
index 76e195780..6e48b56b3 100755
--- a/check/pytest
+++ b/check/pytest
@@ -43,11 +43,10 @@ for arg in "$@"; do
 done
 
 if [ -z "${ACTUALLY_QUIET}" ]; then
-    pytest -c dev_tools/conf/pytest.ini --rootdir="$rootdir" "${PYTEST_ARGS[@]}"
+    pytest --rootdir="$rootdir" "${PYTEST_ARGS[@]}"
 else
     # Filter out lines like "...F....x...      [ 42%]", with coloring.
-    pytest -c dev_tools/conf/pytest.ini \
-           --rootdir="$rootdir" -q --color=yes "${PYTEST_ARGS[@]}" | \
+    pytest --rootdir="$rootdir" -q --color=yes "${PYTEST_ARGS[@]}" | \
         grep -Ev '^(\x1B\[0m)?[\.FEsx]+(\x1B\[36m)?[[:space:]]+\[[[:space:]]*[0-9]+%\](\x1B\[0m)?$'
     exit "${PIPESTATUS[0]}"
 fi
diff --git a/dev_tools/conf/pytest.ini b/dev_tools/conf/pytest.ini
deleted file mode 100644
index 5f7e1fb2d..000000000
--- a/dev_tools/conf/pytest.ini
+++ /dev/null
@@ -1,20 +0,0 @@
-# Copyright 2025 Google LLC
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     https://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-[pytest]
-markers =
-    slow: marks tests as slow (deselect with '-m "not slow"')
-
-filterwarnings =
-    ignore:Skipped assert_qasm_is_consistent_with_unitary because qiskit.*:UserWarning
diff --git a/pyproject.toml b/pyproject.toml
index 2fba4ba31..062008954 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -31,9 +31,16 @@ omit = [
     "./dev_tools/*",
 ]
 
+[tool.pytest.ini_options]
+markers = [
+    """slow: marks tests as slow (deselect with '-m "not slow"')""",
+]
+filterwarnings = [
+    "ignore:Skipped assert_qasm_is_consistent_with_unitary because qiskit.*:UserWarning",
+]
+
 [tool.mypy]
 implicit_optional = true
-
 # TODO: this is temporary for 1.7.0 release. Remove this & fix the errors.
 ignore_errors = true