usethis-python · nathanjmcdougall · Apr 1, 2026 · Apr 1, 2026 · Apr 1, 2026 · Apr 1, 2026
diff --git a/README.md b/README.md
@@ -131,6 +131,7 @@ $ uvx usethis tool ruff
 ✔ Adding Ruff config to 'pyproject.toml'.
 ✔ Selecting Ruff rules 'A', 'C4', 'E4', 'E7', 'E9', 'F', 'FLY', 'FURB', 'I', 'PLE', 'PLR', 'RUF', 'SIM', 'UP' in 'pyproject.toml'.
 ✔ Ignoring Ruff rules 'PLR2004', 'SIM108' in 'pyproject.toml'.
+✔ Running the Ruff formatter.
 ☐ Run 'uv run ruff check --fix' to run the Ruff linter with autofixes.
 ☐ Run 'uv run ruff format' to run the Ruff formatter.
 ```

diff --git a/docs/start/detailed-example.md b/docs/start/detailed-example.md
@@ -6,8 +6,9 @@ The output from usethis is chatty. If you know what you're doing, you can suppre
 $ uvx usethis tool ruff
 ✔ Adding dependency 'ruff' to the 'dev' group in 'pyproject.toml'.
 ✔ Adding Ruff config to 'pyproject.toml'.
-✔ Selecting Ruff rules 'A', 'C4', 'E4', 'E7', 'E9', 'F', 'FLY', 'FURB', 'I', 'PLE', 'PLR', 'RUF', 'SIM'4, 'UP' in 'pyproject.toml'.
+✔ Selecting Ruff rules 'A', 'C4', 'E4', 'E7', 'E9', 'F', 'FLY', 'FURB', 'I', 'PLE', 'PLR', 'RUF', 'SIM', 'UP' in 'pyproject.toml'.
 ✔ Ignoring Ruff rules 'PLR2004', 'SIM108' in 'pyproject.toml'.
+✔ Running the Ruff formatter.
 ☐ Run 'uv run ruff check --fix' to run the Ruff linter with autofixes.
 ☐ Run 'uv run ruff format' to run the Ruff formatter.
 ```
@@ -22,9 +23,11 @@ Let's run through what each line of the output means:
    This line indicates that a set of recommended Ruff rule sets has been selected and added to the `pyproject.toml` configuration. These rules determine what kinds of issues Ruff will check for in your code. The selected rules are based on best practices and are intended to help you maintain high code quality. Most of them have auto-fixes available. You can learn more about the specific rules in the [Ruff documentation](https://docs.astral.sh/ruff/rules).
 4. `✔ Ignoring Ruff rules 'PLR2004', 'SIM108' in 'pyproject.toml'.`  
    This line indicates that certain Ruff rules have been explicitly ignored in the configuration. These rules were deemed less useful or potentially problematic for most projects, so usethis has chosen to disable them by default. You can always modify this list later if you find that you want to enable or disable additional rules.
-5. `☐ Run 'uv run ruff check --fix' to run the Ruff linter with autofixes.`  
+5. `✔ Running the Ruff formatter.`  
+   This line indicates that the Ruff formatter has been automatically applied your codebase.
+6. `☐ Run 'uv run ruff check --fix' to run the Ruff linter with autofixes.`  
    This line is an instruction for you to run the Ruff linter on your codebase. It helps teach you how to use the tool which has just been installed and configured. You're ready to go and explore!
-6. `☐ Run 'uv run ruff format' to run the Ruff formatter.`
+7. `☐ Run 'uv run ruff format' to run the Ruff formatter.`
    Ruff is also a code formatter. Similar to the previous line, this is an instruction for you to run the Ruff formatter on your codebase. This will help ensure that your code adheres to consistent formatting standards.
 
 The key idea is that lines beginning with a check mark (✔) indicate actions that have been successfully completed by usethis, while lines beginning with an empty box (☐) are instructions for you to follow up on.
diff --git a/docs/start/example-usage.md b/docs/start/example-usage.md
@@ -15,6 +15,7 @@ $ uvx usethis tool ruff
 ✔ Adding Ruff config to 'pyproject.toml'.
 ✔ Selecting Ruff rules 'A', 'C4', 'E4', 'E7', 'E9', 'F', 'FLY', 'FURB', 'I', 'PLE', 'PLR', 'RUF', 'SIM', 'UP' in 'pyproject.toml'.
 ✔ Ignoring Ruff rules 'PLR2004', 'SIM108' in 'pyproject.toml'.
+✔ Running the Ruff formatter.
 ☐ Run 'uv run ruff check --fix' to run the Ruff linter with autofixes.
 ☐ Run 'uv run ruff format' to run the Ruff formatter.
 ```

diff --git a/src/usethis/_core/tool.py b/src/usethis/_core/tool.py
@@ -244,6 +244,7 @@ def use_pyproject_fmt(*, remove: bool = False, how: bool = False) -> None:
         tool.add_pre_commit_config()
 
         tool.add_configs()
+        tool.apply()
         tool.print_how_to_use()
     else:
         tool.remove_configs()
@@ -449,6 +450,7 @@ def use_ruff(
             tool.apply_rule_config(rule_config)
         tool.add_pre_commit_config()
 
+        tool.apply()
         tool.print_how_to_use()
     else:
         tool = RuffTool(

diff --git a/src/usethis/_tool/base.py b/src/usethis/_tool/base.py
@@ -114,6 +114,13 @@ def how_to_use_pre_commit_hook_id(self) -> str:
 
         return hook_id
 
+    def apply(self) -> None:
+        """Apply the tool's side effects to the project.
+
+        By default, this is a no-op. Tools that have side effects (e.g. formatters)
+        should override this method to invoke their command via subprocess.
+        """
+
     def is_used(self) -> bool:
         """Whether the tool is being used in the current project.
 

diff --git a/src/usethis/_tool/impl/base/pyproject_fmt.py b/src/usethis/_tool/impl/base/pyproject_fmt.py
@@ -2,12 +2,30 @@
 
 from __future__ import annotations
 
+import contextlib
 from typing import final
 
+from typing_extensions import override
+
+from usethis._backend.dispatch import get_backend
+from usethis._backend.uv.call import call_uv_subprocess
+from usethis._backend.uv.errors import UVSubprocessFailedError
+from usethis._console import tick_print
 from usethis._tool.base import Tool
 from usethis._tool.impl.spec.pyproject_fmt import PyprojectFmtToolSpec
+from usethis._types.backend import BackendEnum
 
 
 @final
 class PyprojectFmtTool(PyprojectFmtToolSpec, Tool):
-    pass
+    @override
+    def apply(self) -> None:
+        """Run pyproject-fmt to format pyproject.toml."""
+        if get_backend() is not BackendEnum.uv:
+            return
+
+        tick_print("Running pyproject-fmt on 'pyproject.toml'.")
+        with contextlib.suppress(UVSubprocessFailedError):
+            call_uv_subprocess(
+                ["run", "pyproject-fmt", "pyproject.toml"], change_toml=False
+            )
diff --git a/src/usethis/_tool/impl/base/ruff.py b/src/usethis/_tool/impl/base/ruff.py
@@ -2,14 +2,17 @@
 
 from __future__ import annotations
 
+import contextlib
 from pathlib import Path
 from typing import TYPE_CHECKING, Literal, final
 
 from pydantic import TypeAdapter, ValidationError
 from typing_extensions import assert_never, override
 
 from usethis._backend.dispatch import get_backend
+from usethis._backend.uv.call import call_uv_subprocess
 from usethis._backend.uv.detect import is_uv_used
+from usethis._backend.uv.errors import UVSubprocessFailedError
 from usethis._config import usethis_config
 from usethis._config_file import DotRuffTOMLManager, RuffTOMLManager
 from usethis._console import how_print, tick_print
@@ -439,3 +442,16 @@ def is_no_subtool_config_present(self) -> bool:
             not self.is_linter_config_present()
             and not self.is_formatter_config_present()
         )
+
+    @override
+    def apply(self) -> None:
+        """Run Ruff formatter on the project."""
+        if get_backend() is not BackendEnum.uv:
+            return
+
+        if not self.is_formatter_used():
+            return
+
+        tick_print("Running the Ruff formatter.")
+        with contextlib.suppress(UVSubprocessFailedError):
+            call_uv_subprocess(["run", "ruff", "format"], change_toml=False)
diff --git a/tests/usethis/_core/test_core_tool.py b/tests/usethis/_core/test_core_tool.py
@@ -2276,6 +2276,7 @@ def test_added(self, uv_init_dir: Path, capfd: pytest.CaptureFixture[str]):
                 out, _ = capfd.readouterr()
                 assert out == (
                     "✔ Adding pyproject-fmt config to 'pyproject.toml'.\n"
+                    "✔ Running pyproject-fmt on 'pyproject.toml'.\n"
                     "☐ Run 'uv run pyproject-fmt pyproject.toml' to run pyproject-fmt.\n"
                 )
 
@@ -2295,6 +2296,7 @@ def test_added(self, uv_init_dir: Path, capfd: pytest.CaptureFixture[str]):
                     "✔ Adding dependency 'pyproject-fmt' to the 'dev' group in 'pyproject.toml'.\n"
                     "☐ Install the dependency 'pyproject-fmt'.\n"
                     "✔ Adding pyproject-fmt config to 'pyproject.toml'.\n"
+                    "✔ Running pyproject-fmt on 'pyproject.toml'.\n"
                     "☐ Run 'uv run pyproject-fmt pyproject.toml' to run pyproject-fmt.\n"
                 )
 
@@ -2328,6 +2330,7 @@ def test_pre_commit_integration(
                 "☐ Install the dependency 'pyproject-fmt'.\n"
                 "✔ Adding hook 'pyproject-fmt' to '.pre-commit-config.yaml'.\n"
                 "✔ Adding pyproject-fmt config to 'pyproject.toml'.\n"
+                "✔ Running pyproject-fmt on 'pyproject.toml'.\n"
                 "☐ Run 'uv run pyproject-fmt pyproject.toml' to run pyproject-fmt.\n"
             )
 
@@ -3123,6 +3126,7 @@ def test_stdout(self, uv_init_dir: Path, capfd: pytest.CaptureFixture[str]):
                 "✔ Adding Ruff config to 'pyproject.toml'.\n"
                 "✔ Selecting Ruff rules 'A', 'C4', 'E4', 'E7', 'E9', 'F', 'FLY', 'FURB', 'I', 'PLE', 'PLR', 'RUF', 'SIM', 'UP' in 'pyproject.toml'.\n"
                 "✔ Ignoring Ruff rules 'PLR2004', 'SIM108' in 'pyproject.toml'.\n"
+                "✔ Running the Ruff formatter.\n"
                 "☐ Run 'uv run ruff check --fix' to run the Ruff linter with autofixes.\n"
                 "☐ Run 'uv run ruff format' to run the Ruff formatter.\n"
             )
@@ -3182,6 +3186,7 @@ def test_existing_ruff_toml(
                 "✔ Adding dependency 'ruff' to the 'dev' group in 'pyproject.toml'.\n"
                 "☐ Install the dependency 'ruff'.\n"
                 "✔ Adding Ruff config to 'ruff.toml'.\n"
+                "✔ Running the Ruff formatter.\n"
                 "☐ Run 'uv run ruff check --fix' to run the Ruff linter with autofixes.\n"
                 "☐ Run 'uv run ruff format' to run the Ruff formatter.\n"
             )
@@ -3274,10 +3279,10 @@ def test_only_add_formatter(
                 "✔ Adding dependency 'ruff' to the 'dev' group in 'pyproject.toml'.\n"
                 "☐ Install the dependency 'ruff'.\n"
                 "✔ Adding Ruff config to 'pyproject.toml'.\n"
+                "✔ Running the Ruff formatter.\n"
                 "☐ Run 'uv run ruff format' to run the Ruff formatter.\n"
             )
 
-    class TestRemove:
         @pytest.mark.usefixtures("_vary_network_conn")
         def test_config_file(self, uv_init_dir: Path):
             # Arrange

diff --git a/tests/usethis/_tool/impl/base/test_pyproject_fmt.py b/tests/usethis/_tool/impl/base/test_pyproject_fmt.py
@@ -2,9 +2,11 @@
 
 import pytest
 
+from usethis._config import usethis_config
 from usethis._config_file import files_manager
 from usethis._test import change_cwd
 from usethis._tool.impl.base.pyproject_fmt import PyprojectFmtTool
+from usethis._types.backend import BackendEnum
 
 
 class TestPyprojectFmtTool:
@@ -23,3 +25,28 @@ def test_uv_only(self, tmp_path: Path, capfd: pytest.CaptureFixture[str]):
             assert out == (
                 "☐ Run 'uv run pyproject-fmt pyproject.toml' to run pyproject-fmt.\n"
             )
+
+    class TestApply:
+        def test_uv_backend(self, uv_init_dir: Path, capfd: pytest.CaptureFixture[str]):
+            # Act
+            with change_cwd(uv_init_dir), files_manager():
+                PyprojectFmtTool().apply()
+
+            # Assert
+            out, err = capfd.readouterr()
+            assert not err
+            assert out == "✔ Running pyproject-fmt on 'pyproject.toml'.\n"
+
+        def test_none_backend(self, tmp_path: Path, capfd: pytest.CaptureFixture[str]):
+            # Act
+            with (
+                change_cwd(tmp_path),
+                usethis_config.set(backend=BackendEnum.none),
+                files_manager(),
+            ):
+                PyprojectFmtTool().apply()
+
+            # Assert
+            out, err = capfd.readouterr()
+            assert not err
+            assert out == ""
diff --git a/tests/usethis/_tool/impl/base/test_ruff.py b/tests/usethis/_tool/impl/base/test_ruff.py
@@ -2,10 +2,12 @@
 
 import pytest
 
+from usethis._config import usethis_config
 from usethis._config_file import DotRuffTOMLManager, RuffTOMLManager, files_manager
 from usethis._file.pyproject_toml.io_ import PyprojectTOMLManager
 from usethis._test import change_cwd
 from usethis._tool.impl.base.ruff import RuffTool
+from usethis._types.backend import BackendEnum
 
 
 class TestRuffTool:
@@ -568,3 +570,42 @@ def test_pyproject_toml_exists(self, tmp_path: Path):
             assert not (tmp_path / ".ruff.toml").exists()
             assert (tmp_path / "pyproject.toml").exists()
             assert not (tmp_path / "ruff.toml").exists()
+
+    class TestApply:
+        def test_uv_backend_formatter_used(
+            self, uv_init_dir: Path, capfd: pytest.CaptureFixture[str]
+        ):
+            # Act
+            with change_cwd(uv_init_dir), files_manager():
+                RuffTool(formatter_detection="always").apply()
+
+            # Assert
+            out, err = capfd.readouterr()
+            assert not err
+            assert out == "✔ Running the Ruff formatter.\n"
+
+        def test_uv_backend_formatter_not_used(
+            self, uv_init_dir: Path, capfd: pytest.CaptureFixture[str]
+        ):
+            # Act
+            with change_cwd(uv_init_dir), files_manager():
+                RuffTool(formatter_detection="never").apply()
+
+            # Assert
+            out, err = capfd.readouterr()
+            assert not err
+            assert out == ""
+
+        def test_none_backend(self, tmp_path: Path, capfd: pytest.CaptureFixture[str]):
+            # Act
+            with (
+                change_cwd(tmp_path),
+                usethis_config.set(backend=BackendEnum.none),
+                files_manager(),
+            ):
+                RuffTool(formatter_detection="always").apply()
+
+            # Assert
+            out, err = capfd.readouterr()
+            assert not err
+            assert out == ""
diff --git a/tests/usethis/_ui/interface/test_tool.py b/tests/usethis/_ui/interface/test_tool.py
@@ -512,6 +512,7 @@ def test_readme_example(self, uv_init_dir: Path):
 ✔ Adding Ruff config to 'pyproject.toml'.
 ✔ Selecting Ruff rules 'A', 'C4', 'E4', 'E7', 'E9', 'F', 'FLY', 'FURB', 'I', 'PLE', 'PLR', 'RUF', 'SIM', 'UP' in 'pyproject.toml'.
 ✔ Ignoring Ruff rules 'PLR2004', 'SIM108' in 'pyproject.toml'.
+✔ Running the Ruff formatter.
 ☐ Run 'uv run ruff check --fix' to run the Ruff linter with autofixes.
 ☐ Run 'uv run ruff format' to run the Ruff formatter.
 """