diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index aa1de96..da2465e 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -11,6 +11,6 @@ jobs:
       - name: Build and publish to pypi
         uses: JRubics/poetry-publish@v2.0
         with:
-          python_version: "3.9.17"
+          python_version: "3.12"
           poetry_install_options: "--without dev"
           pypi_token: ${{ secrets.PYPI_API_TOKEN }}
diff --git a/.readthedocs.yml b/.readthedocs.yml
index 2eba8b1..a1c95fa 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -6,7 +6,7 @@ build:
   os: ubuntu-20.04
   tools:
     # Keep version in sync with tox.ini (docs and gh-actions).
-    python: "3.9"
+    python: "3.12"
 
 python:
   install:
diff --git a/tox.ini b/tox.ini
index 973140e..30ad527 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,7 +7,7 @@
 skipdist = True
 skip_missing_interpreters = True
 isolated_build = True
-envlist = py39, py310, py311, py312, docs, pre-commit
+envlist = py{39,310,311,312}, docs, pre-commit
 
 # Keep python version for docs in sync with docs testenv:docs and .readthedocs.yml
 [gh-actions]
@@ -22,8 +22,8 @@ python =
 [testenv:.package]
 install_command =
 
-
 [testenv]
+description = run unit tests
 skip_install = true
 allowlist_externals = poetry
 commands_pre = poetry install
@@ -33,24 +33,26 @@ commands =
 [testenv:docs]
 # Keep basepython in sync with gh-actions and .readthedocs.yml.
 description = invoke sphinx-build to build the HTML docs
-basepython = python3.9
+basepython = python3.12
 commands =
     poetry run sphinx-build -d "{toxworkdir}/docs_doctree" docs "{toxworkdir}/docs_out" --color -W -bhtml {posargs}
     python -c 'import pathlib; print("documentation available under file://\{0\}".format(pathlib.Path(r"{toxworkdir}") / "docs_out" / "index.html"))'
 
 [testenv:serve-docs]
 # Keep basepython in sync with gh-actions and .readthedocs.yml.
-description = live serve docs with sphinx-autobuild
-basepython = python3.9
+description = live-serve docs with sphinx-autobuild
+basepython = python3.12
 commands =
     poetry run sphinx-autobuild --port=0 --open-browser docs docs/_build/html
 
 [testenv:pre-commit]
-basepython = python3.9
+description = run linters and formatters
+basepython = python3.12
 commands =
     poetry run pre-commit run --all-files
 
 [testenv:typing]
-basepython = python3.9
+description = run type checks
+basepython = python3.12
 commands =
     poetry run mypy ./src