diff --git a/.github/workflows/test-and-tag.yml b/.github/workflows/test-and-tag.yml
index 6341195..53a2a4c 100644
--- a/.github/workflows/test-and-tag.yml
+++ b/.github/workflows/test-and-tag.yml
@@ -17,22 +17,28 @@ on:
 jobs:
   run-unit-tests:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        # If updating this list of python versions, you also need to update tox config in pyproject.toml
+        python-version: ['3.10', '3.11', '3.12']
     permissions:
         contents: write
     steps:
     - uses: actions/checkout@v4
 
-    - name: Setup python
-      id: setup_python
+    - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v5
       with:
-        python-version: '3.10'
+        python-version: ${{ matrix.python-version }}
+
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        python -m pip install -r requirements-test.txt
 
     - name: Run tests
       run: |
-        python -m venv .venv
-        source .venv/bin/activate && python -m pip install --upgrade pip && pip install -r requirements-dev.txt
-        pytest
+        tox
 
   create-release:
     runs-on: ubuntu-latest
diff --git a/README.md b/README.md
index 835e1de..6558b7a 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,12 @@ Install pre-commit hook: https://github.com/communitiesuk/funding-service-design
 If you add any packages needed by services that consume `fsd_utils`, add them into `pyproject.yaml`.
 
 # Testing
-[Testing in Python repos](https://github.com/communitiesuk/funding-service-design-workflows/blob/main/readmes/python-repos-testing.md)
+
+Tests in this repository run using `pytest`, as per our standardise [Testing in Python repos](https://github.com/communitiesuk/funding-service-design-workflows/blob/main/readmes/python-repos-testing.md) practice.
+
+However, because this is a shared utils library that can be installed under different conditions (mainly Python or Flask versions), we matrix test the combinations using [tox](https://tox.wiki/en/4.15.1/).
+
+To run tests via tox, `pip install -r requirements-test.txt` and then simply run `tox`. To run suites in parallel, run eg `tox -p 8`.
 
 # Releasing
 To create a new release of funding-service-design-utils (note no longer need to manually update the version):
diff --git a/pyproject.toml b/pyproject.toml
index 02f5d72..1121fdc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,6 +25,7 @@ dependencies = [
     "PyYAML>=6.0,<7.0",
     "python-dotenv>=0.20.0,<0.21.0",
     "rich>=12.4.4,<13.0.0",
+    # If adding support for a new major/minor Flask version below, remember to add a tox env to matrix test it.
     "Flask>=2.1.1,<3.0.0",
     "python-json-logger>=2.0.2,<3.0.0",
     "gunicorn>=20.1.0,<21.0.0",
@@ -42,3 +43,51 @@ dependencies = [
 
 [project.urls]
 "Homepage" = "https://github.com/communitiesuk/funding-service-design-utils"
+
+[tool.tox]
+legacy_tox_ini = """
+[tox]
+envlist = py310-A, py310-B, py311-A, py311-B, py312-A, py312-B
+
+[gh-actions]
+python =
+    3.10: py310
+    3.11: py311
+    3.12: py312
+
+[testenv]
+commands = py.test
+deps =
+    pytest
+    -r requirements-dev.txt
+
+[testenv:py310-A]
+basepython = python3.10
+deps = {[testenv]deps}
+    Flask>=2.2,<2.3
+
+[testenv:py310-B]
+basepython = python3.10
+deps = {[testenv]deps}
+    Flask>=2.3,<3.0
+
+[testenv:py311-A]
+basepython = python3.11
+deps = {[testenv]deps}
+    Flask>=2.2,<2.3
+
+[testenv:py311-B]
+basepython = python3.11
+deps = {[testenv]deps}
+    Flask>=2.3,<3.0
+
+[testenv:py312-A]
+basepython = python3.12
+deps = {[testenv]deps}
+    Flask>=2.2,<2.3
+
+[testenv:py312-B]
+basepython = python3.12
+deps = {[testenv]deps}
+    Flask>=2.3,<3.0
+"""
diff --git a/requirements-test.txt b/requirements-test.txt
new file mode 100644
index 0000000..606a02d
--- /dev/null
+++ b/requirements-test.txt
@@ -0,0 +1,3 @@
+# This file installs the dependencies required for running tests via tox, which we use in our github workflow (CI).
+tox==4.15.1
+tox-gh-actions==3.2.0