diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 234448fd..115577ab 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -3,10 +3,11 @@ tests, ensure they build and pass, and ensure that `pylint` and `mypy`
 are happy with your code.
 
 - Install `pip` following their [documentation](https://pip.pypa.io/en/stable/installation/).
-- Install development dependencies: `pip install pylint pytest mypy sphinx`
+- Install development dependencies: `pip install pylint pytest mypy sphinx black`
 - Install docs dependencies: `pip install -r docs/requirements.txt` (might need to comment out the build123d line in that file)
 - Install `build123d` in editable mode from current dir:  `pip install -e .`
 - Run tests with: `python -m pytest`
 - Build docs with: `cd docs && make html`
 - Check added files' style with: `pylint <path/to/file.py>` 
 - Check added files' type annotations with: `mypy <path/to/file.py>`
+- Run black formatter against files' changed: `black --config pyproject.toml <path/to/file.py>` (where the pyproject.toml is from this project's repository)
diff --git a/pyproject.toml b/pyproject.toml
index c77ce0e3..514aadb1 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -61,3 +61,6 @@ exclude = ["build123d._dev"]
 [tool.setuptools_scm]
 write_to = "src/build123d/_version.py"
 
+[tool.black]
+target-version = ["py39", "py310", "py311", "py312"]
+line-length = 88