I moved tidyfeed from setup.py to a PEP 621 pyproject.toml on the setuptools backend. I haven't checked it with a build yet: I couldn't run any commands in this session. The commands for that are below. pyproject.toml (new, excerpt) [build-system] requires = ["setuptools>=77"] build-backend = "setuptools.build_meta" [project] name = "tidyfeed" dynamic = ["version"] readme = "README.md" license = "MIT" license-files = ["LICENSE*"] requires-python = ">=3.9" dependencies = [ "feedparser>=6.0", "httpx>=0.24,<1.0", 'tomli>=2.0; python_version < "3.11"', ] (… authors, classifiers without the License :: line, keywords, optional-dependencies cli/dev, urls, scripts …) [tool.setuptools] # Classic setup.py did not set include_package_data, so it was false. # The pyproject default is true; keep the old behavior explicitly. include-package-data = false [tool.setuptools.packages.find] # Mirrors find_packages(exclude=["tests", "tests.*"]). where = ["."] exclude = ["tests", "tests.*"] namespaces = false [tool.setuptools.dynamic] version = {attr = "tidyfeed.__version__"} [tool.pytest.ini_options] testpaths = ["tests"] addopts = "-ra --strict-markers" setup.cfg (cut down): only [flake8] stays, because flake8 does not read pyproject.toml. Main points - Nothing in the package should change: dependencies, extras, the tidyfeed command and >=3.9 are the same. Version strings and markers are unchanged. - Version still comes from one place, tidyfeed/__init__.py line 3. Setuptools now reads it with attr instead of the regex. - No setup.py shim needed: nothing in it was computed at build time. Behavior changes (check these) - License: License: MIT becomes License-Expression: MIT, and I removed the License :: OSI Approved :: MIT License classifier (deprecated; setuptools 77+ refuses it next to a license expression). - Homepage: the Home-page: line becomes Project-URL: Homepage. - setuptools 77 or newer is now required to build. Builds with --no-build-isolation and an older setuptools will fail. Needs your decision: None. dev stays an extra (not moved to [dependency-groups]). Delete after verifying: setup.py. I have not deleted anything myself. Verification (not run) python -m pip install --upgrade build twine python -m build --outdir dist-before # on the old state python -m build --outdir dist-after # on the migrated state python -m twine check dist-after/* Compare the wheel file lists, METADATA and entry_points.txt. You should only see the license and Homepage differences above, plus a new Metadata-Version. Full field mapping in MIGRATION_REPORT.md.