diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..a094b90
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,12 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_size = 4
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[{*.yaml,*.yml}]
+indent_size = 2
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
new file mode 100644
index 0000000..2390d8c
--- /dev/null
+++ b/.github/dependabot.yml
@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    groups:
+      github-actions:
+        patterns:
+          - "*"
diff --git a/.github/workflows/readme_example.yaml b/.github/workflows/readme_example.yaml
new file mode 100644
index 0000000..26c5c5b
--- /dev/null
+++ b/.github/workflows/readme_example.yaml
@@ -0,0 +1,74 @@
+# This workflow exists for several purposes:
+#
+# * Ensure that the example in the README is functional.
+# * Ensure that the desired YAML formatting is enforced.
+# * Ensure that the example action versions are maintained.
+#
+# Update PRs submitted by Dependabot should trigger pre-commit.ci,
+# which will synchronize changes to this file into the README.
+#
+
+name: "📘 README"
+
+on:
+  pull_request:
+  push:
+    branches:
+      - "main"
+      - "releases"
+  schedule:
+    - cron: "27 19 * * *"
+
+jobs:
+  readme_example:
+    name: "Test README code (${{ matrix.os.name }})"
+    strategy:
+      matrix:
+        os:
+          - name: "Linux"
+            runner: "ubuntu-latest"
+          - name: "macOS"
+            runner: "macos-latest"
+          - name: "Windows"
+            runner: "windows-latest"
+      fail-fast: false
+
+    runs-on: "${{ matrix.os.runner }}"
+    steps:
+      # START_README_EXAMPLE_BLOCK
+      - uses: "actions/setup-python@v4"
+        with:
+          python-version: |
+            pypy3.10
+            3.11
+
+      - uses: "kurtmckee/detect-pythons@main"
+
+      - uses: "actions/cache@v3"
+        id: "restore-cache"
+        with:
+          # You may need to augment the list of files to hash.
+          # For example, you might add 'requirements/*.txt' or 'pyproject.toml'.
+          key: "${{ hashFiles('.python-identifiers') }}"
+          path: |
+            .tox/
+            .venv/
+
+      - name: "Identify .venv path"
+        shell: "bash"
+        run: "echo 'venv-path=.venv/${{ runner.os == 'Windows' && 'Scripts' || 'bin' }}' >> $GITHUB_ENV"
+
+      - name: "Create a virtual environment"
+        if: "steps.restore-cache.outputs.cache-hit == false"
+        run: |
+          python -m venv .venv
+          ${{ env.venv-path }}/python -m pip install --upgrade pip setuptools wheel
+
+          # You may need to customize what gets installed next.
+          # However, tox is able to run test suites against multiple Pythons,
+          # so it's a helpful tool for efficient testing.
+          ${{ env.venv-path }}/pip install tox
+
+      - name: "Run the test suite against all installed Pythons"
+        run: "${{ env.venv-path }}/tox"
+      # END_README_EXAMPLE_BLOCK
diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
new file mode 100644
index 0000000..e5057f2
--- /dev/null
+++ b/.github/workflows/test.yaml
@@ -0,0 +1,37 @@
+name: "🔬 Test"
+
+on:
+  push:
+    branches:
+      - "main"
+
+jobs:
+  test:
+    name: "Test on ${{ matrix.os.name }}"
+
+    strategy:
+      matrix:
+        os:
+          - name: "Linux"
+            runner: "ubuntu-latest"
+          - name: "macOS"
+            runner: "macos-latest"
+          - name: "Windows"
+            runner: "windows-latest"
+      fail-fast: false
+
+    runs-on: "${{ matrix.os.runner }}"
+    steps:
+      - name: "Use it!"
+        id: "detector"
+        uses: "kurtmckee/detect-pythons@main"
+
+      - name: "Print it!"
+        shell: "bash"
+        run: |
+          echo '${{ steps.detector.outputs.python-identifiers }}'
+
+      - name: "Display it!"
+        shell: "bash"
+        run: |
+          cat .python-identifiers
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..bee8a64
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+__pycache__
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..1f2c6ee
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,76 @@
+ci:
+  autoupdate_schedule: "monthly"
+
+repos:
+  - repo: "meta"
+    hooks:
+      - id: "check-hooks-apply"
+      - id: "check-useless-excludes"
+
+  - repo: "https://github.com/pre-commit/pre-commit-hooks"
+    rev: "v4.5.0"
+    hooks:
+      - id: "trailing-whitespace"
+      - id: "end-of-file-fixer"
+      - id: "check-yaml"
+      - id: "check-added-large-files"
+
+  - repo: "https://github.com/psf/black-pre-commit-mirror"
+    rev: "23.9.1"
+    hooks:
+      - id: "black"
+        language_version: "python3.8"
+
+  - repo: "https://github.com/pycqa/isort"
+    rev: "5.12.0"
+    hooks:
+      - id: "isort"
+
+  - repo: "https://github.com/pycqa/flake8"
+    rev: "6.1.0"
+    hooks:
+      - id: "flake8"
+
+  - repo: "https://github.com/editorconfig-checker/editorconfig-checker.python"
+    rev: "2.7.3"
+    hooks:
+      - id: "editorconfig-checker"
+        # The README contains YAML syntax that is indented with 2 spaces.
+        # The .editorconfig file will continue to require 4 spaces,
+        # and this pre-commit hook will ignore the README.
+        exclude: "README.rst"
+
+  - repo: "local"
+    hooks:
+      - id: "sync-identify-code"
+        name: "Synchronize identify.py source code into 'detector.sh'"
+        language: "python"
+        entry: "python src/detect_pythons/sync_identify_code.py"
+        files: "^src/detect_pythons/identify.py$"
+
+  - repo: "https://github.com/shellcheck-py/shellcheck-py"
+    rev: "v0.9.0.6"
+    hooks:
+      - id: "shellcheck"
+        args:
+          - "--shell=bash"
+
+  - repo: "local"
+    hooks:
+      - id: "sync-detector-code"
+        name: "Synchronize detector source code into 'action.yml'"
+        language: "python"
+        entry: "python src/detect_pythons/sync_detector_code.py"
+        files: "^src/detect_pythons/detector.*$"
+      - id: "sync-readme-example"
+        name: "Synchronize a functional example into the README"
+        language: "python"
+        entry: "python src/detect_pythons/sync_readme_example.py"
+        always_run: true
+        pass_filenames: false
+
+  - repo: "https://github.com/python-jsonschema/check-jsonschema"
+    rev: "0.27.0"
+    hooks:
+      - id: "check-github-workflows"
+      - id: "check-dependabot"
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..a8c5822
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright 2023 Kurt McKee <contactme@kurtmckee.org>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.rst b/README.rst
new file mode 100644
index 0000000..8cc758c
--- /dev/null
+++ b/README.rst
@@ -0,0 +1,170 @@
+Detect Python interpreters
+##########################
+
+*Robust cache-busting based on Python implementations, versions, and architectures.*
+
+----
+
+Purpose
+=======
+
+If you're caching Python virtual environments, or tox environments,
+or even build artifacts that depend on a particular Python version,
+you need robust cache busting to ensure that your caches are invalidated
+when a new Python version is released.
+
+``detect-pythons`` provides that much-needed cache busting.
+
+It detects all Python executables in every directory on the ``$PATH``
+and identifies:
+
+*   The Python interpreter (CPython, PyPy, or GraalPy)
+*   The Python version (like "3.12.0")
+    or the Python ABI version (like "3.12")
+*   The target architecture (like "x64")
+
+In most cases, the path to the executable already contains this information
+so it's not necessary to run the Python interpreter to extract any info.
+There are some exceptions, however;
+these are covered in the "Implementation" section below.
+
+
+Usage
+=====
+
+The following example demonstrates how ``detect-pythons`` can be used
+when caching a Python virtual environment stored in ``.venv/``
+and tox test environments stored in ``.tox/``.
+
+
+..  START_EXAMPLE_YAML_BLOCK
+..  code-block:: yaml
+
+    - uses: "actions/setup-python@v4"
+      with:
+        python-version: |
+          pypy3.10
+          3.11
+
+    - uses: "kurtmckee/detect-pythons@main"
+
+    - uses: "actions/cache@v3"
+      id: "restore-cache"
+      with:
+        # You may need to augment the list of files to hash.
+        # For example, you might add 'requirements/*.txt' or 'pyproject.toml'.
+        key: "${{ hashFiles('.python-identifiers') }}"
+        path: |
+          .tox/
+          .venv/
+
+    - name: "Identify .venv path"
+      shell: "bash"
+      run: "echo 'venv-path=.venv/${{ runner.os == 'Windows' && 'Scripts' || 'bin' }}' >> $GITHUB_ENV"
+
+    - name: "Create a virtual environment"
+      if: "steps.restore-cache.outputs.cache-hit == false"
+      run: |
+        python -m venv .venv
+        ${{ env.venv-path }}/python -m pip install --upgrade pip setuptools wheel
+
+        # You may need to customize what gets installed next.
+        # However, tox is able to run test suites against multiple Pythons,
+        # so it's a helpful tool for efficient testing.
+        ${{ env.venv-path }}/pip install tox
+
+    - name: "Run the test suite against all installed Pythons"
+      run: "${{ env.venv-path }}/tox"
+..  END_EXAMPLE_YAML_BLOCK
+
+
+Inputs
+======
+
+By default, the action writes to a file named ``.python-identifiers``,
+which can then be passed to GitHub's ``hashFiles`` function
+for convenient cache-busting.
+
+You can customize the path and filename
+by modifying the input variable ``identifiers-filename``:
+
+..  code-block:: yaml
+
+    - uses: "kurtmckee/detect-pythons@main"
+      with:
+        identifiers-filename: "favored_filename.txt"
+
+To prevent writing a file at all,
+set ``identifiers-filename`` to an empty string:
+
+..  code-block:: yaml
+
+    - uses: "kurtmckee/detect-pythons@main"
+      with:
+        identifiers-filename: ""
+
+
+Outputs
+=======
+
+In addition to writing to a file,
+the action creates an output named ``python-identifiers``.
+This may be useful in other contexts.
+
+
+Implementation
+==============
+
+The action tries to find all Python interpreters available on the ``$PATH``
+and ensure that critical information about each interpreter is included
+in the action output:
+
+*   Implementation
+*   Version
+*   Architecture
+
+
+Cached Python interpreters
+--------------------------
+
+GitHub runners have common CPython and PyPy versions pre-installed.
+These are installed under ``$RUNNER_TOOL_CACHE`` in informative directory paths,
+so the paths are used without executing the interpreters.
+
+..  csv-table::
+    :header: "Platform", "Sample path under ``$RUNNER_TOOL_CACHE``"
+
+    "Linux", "``/opt/hostedtoolcache/Python/3.11.6/x64/bin``"
+    "macOS", "``/Users/runner/hostedtoolcache/PyPy/3.10.13/x64/bin``"
+    "Windows", "``C:\hostedtoolcache\windows\Python\3.11.6\x64``"
+
+
+System CPython interpreters
+---------------------------
+
+GitHub's Linux and macOS runners have system CPython interpreters installed.
+These are available at paths like ``/usr/bin/python``,
+which contains no useful information.
+
+For these interpreters, the interpreter is executed
+and the value of ``sysconfig.get_config_var("EXT_SUFFIX")`` is extracted.
+This results in a value like the following:
+
+..  csv-table::
+    :header: "Platform", "Sample ``EXT_SUFFIX`` value"
+
+    "Linux", "``.cpython-310-x86_64-linux-gnu.so``"
+    "macOS", "``.cpython-311-darwin.so``"
+
+
+...other
+--------
+
+At the time of writing, GitHub's current macOS runner has CPython 2.7 pre-installed
+and available on the ``$PATH``.
+It doesn't have an ``EXT_SUFFIX`` config value, so this action constructs one.
+
+..  csv-table::
+    :header: "Platform", "Constructed ``EXT_SUFFIX`` equivalent"
+
+    "macOS", "``.cpython-27-darwin``"
diff --git a/TODO.rst b/TODO.rst
new file mode 100644
index 0000000..72652c8
--- /dev/null
+++ b/TODO.rst
@@ -0,0 +1,5 @@
+*   Expand README
+*   Create ``releases`` branch for tagging and such
+*   Add pre-commit hook to check README against latest tagged SHA
+*   Add test suite that can run locally
+*   Add test suite that verifies expected outputs in CI
diff --git a/action.yml b/action.yml
new file mode 100644
index 0000000..b725ed0
--- /dev/null
+++ b/action.yml
@@ -0,0 +1,172 @@
+author: "Kurt McKee"
+name: "Detect installed Python interpreters"
+description: |
+  Detect installed Python interpreters and output them as "python-identifiers".
+  This can be useful for cache busting of tox, virtual environments,
+  and other items that are sensitive to changes in Python implementations and versions.
+
+  Only Python interpreters named "python" in the $PATH will be found.
+
+inputs:
+  identifiers-filename:
+    description: |
+      A filename to write the ``python-identifiers`` output to.
+      Suitable for use in with the ``hashFiles`` function.
+
+      To prevent any file from being written, use a blank string.
+    required: false
+    default: ".python-identifiers"
+
+outputs:
+  python-identifiers:
+    description: |
+      A string of sorted Python identifiers.
+
+      In most cases the identifiers will be paths,
+      but for system Pythons, 'sysconfig.get_config_var("EXT_SUFFIX")' will be included.
+
+      The string will be separated by OS-specific PATH separators;
+      ":" is used on Linux and macOS, and ";" is used on Windows.
+    value: "${{ steps.final-step.outputs.python-identifiers }}"
+
+runs:
+  using: "composite"
+  steps:
+    - name: "Detect Pythons on Linux / macOS"
+      id: "linux"
+      if: "runner.os != 'windows'"
+      shell: "bash"
+      # Do not edit the 'run' code below.
+      # It is copied from 'detector.sh' by a pre-commit hook.
+      # START: detector.sh
+      run: |
+        true > /dev/null  # No-op to prevent YAML syntax errors.
+        # Do not modify the Python code below.
+        # It is copied from 'identify.py' by a pre-commit hook.
+        python_code=$(
+        cat <<'identify.py_SOURCE_CODE'
+        from __future__ import print_function
+
+        import sysconfig
+
+
+        def main():
+            ext_suffix = sysconfig.get_config_var("EXT_SUFFIX")
+            if ext_suffix is not None:
+                print(ext_suffix)
+            else:
+                # Python 2.7 on GitHub macOS runners
+                import platform
+
+                print(
+                    "." + platform.python_implementation().lower(),
+                    sysconfig.get_config_var("py_version_nodot"),
+                    sysconfig.get_config_var("MACHDEP"),
+                    sep="-",
+                )
+
+
+        if __name__ == "__main__":
+            main()
+        identify.py_SOURCE_CODE
+        )
+
+        # Search paths in $PATH for Python interpreters.
+        IFS=: read -r -a all_paths <<< "$PATH"
+
+        # Detect Python interpreters.
+        paths=()
+        for path in "${all_paths[@]}"; do
+            # Interpreters in RUNNER_TOOL_CACHE have directory names that include:
+            #
+            # * The implementation (like "Python" or "PyPy")
+            # * A version (like "3.10.12")
+            # * The architecture (like "x64")
+            #
+            # In such cases, the path can be used as the identifier.
+            if [[ "${path/#${RUNNER_TOOL_CACHE}/}" != "${path}" ]]; then
+                # Check for bin/python first;
+                # this results in duplicate paths which are later removed.
+                if [[ -x "${path}/bin/python" ]]; then
+                    paths+=("${path}/bin")
+                elif [[ -x "${path}/python" ]]; then
+                    paths+=("${path}")
+                fi
+            else
+                # System Pythons (e.g. /usr/bin/python) have nothing unique in the path.
+                # In such cases, it's necessary to run the executable to get something unique.
+                if [[ -x "${path}/python" ]]; then
+                    paths+=("${path}")
+                    paths+=("$(echo "${python_code}" | "${path}/python" -)")
+                fi
+            fi
+        done
+
+        # Sort the paths, ensure each path is unique, and create the output result.
+        result="$(
+            echo "${paths[*]}" \
+            | tr ' ' '\n' \
+            | sort \
+            | uniq \
+            | tr '\n' ':'
+        )"
+
+        # Trim trailing colons.
+        result="${result%:}"
+
+        # Output path information.
+        # This must be the final line because it will be automatically transformed to:
+        #
+        #     echo "python-identifiers=${result}" > "$GITHUB_OUTPUT"
+        #
+        echo "python-identifiers=${result}" > "$GITHUB_OUTPUT"
+      # END: detector.sh
+
+    - name: "Detect Pythons on Windows"
+      id: "windows"
+      if: "runner.os == 'windows'"
+      shell: "powershell"
+      # Do not edit the 'run' code below.
+      # It is copied from 'detector.ps1' by a pre-commit hook.
+      # START: detector.ps1
+      run: |
+        $true | Out-Null  # No-op to prevent YAML syntax errors.
+        # Search paths in $PATH for Python interpreters.
+        $all_paths = $env:PATH -split ";"
+
+        # Detect Python interpreters.
+        $paths = @()
+        foreach ($path in $all_paths) {
+            # Only consider paths in RUNNER_TOOL_CACHE.
+            if ($path.StartsWith($env:RUNNER_TOOL_CACHE)) {
+                if (Test-Path "$path\python.exe") {
+                    $paths += $path
+                }
+            }
+        }
+
+        # Sort the paths, ensure each path is unique, and create the output result.
+        $result = (
+            $paths `
+            | Sort-Object `
+            | Get-Unique
+        ) -join ";"
+
+        # Output path information.
+        # This must be the final line because it will be automatically transformed to:
+        #
+        #     Write-Output "python-identifiers=$result" > "$env:GITHUB_OUTPUT"
+        #
+        Write-Output "python-identifiers=$result" > "$env:GITHUB_OUTPUT"
+      # END: detector.ps1
+
+    - name: "Output"
+      id: "final-step"
+      shell: "bash"
+      run: |
+        COMBINED='${{ steps.linux.outputs.python-identifiers }}${{ steps.windows.outputs.python-identifiers }}'
+        echo "python-identifiers=${COMBINED}" > "$GITHUB_OUTPUT"
+        if [ ! -z '${{ inputs.identifiers-filename }}' ]; then
+            echo "Writing Python identifiers to '${{ inputs.identifiers-filename }}'"
+            echo "${COMBINED}" > '${{ inputs.identifiers-filename }}'
+        fi
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..885838a
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,26 @@
+[tool.poetry]
+name = "detect_pythons"
+version = "1.0.0"
+description = "A GitHub action to detect installed Pythons. Suitable for cache-busting."
+authors = ["Kurt McKee <contactme@kurtmckee.org>"]
+license = "MIT"
+readme = "README.rst"
+
+
+[tool.poetry.scripts]
+identify = "detect_pythons.identify:main"
+sync-detector-code = "detect_pythons.sync_detector_code:main"
+sync-identify-code = "detect_pythons.sync_identify_code:main"
+
+
+[tool.poetry.dependencies]
+python = ">=3.8"
+
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"
+
+
+[tool.isort]
+profile = "black"
diff --git a/src/detect_pythons/__init__.py b/src/detect_pythons/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/detect_pythons/detector.ps1 b/src/detect_pythons/detector.ps1
new file mode 100644
index 0000000..d6ee438
--- /dev/null
+++ b/src/detect_pythons/detector.ps1
@@ -0,0 +1,27 @@
+# Search paths in $PATH for Python interpreters.
+$all_paths = $env:PATH -split ";"
+
+# Detect Python interpreters.
+$paths = @()
+foreach ($path in $all_paths) {
+    # Only consider paths in RUNNER_TOOL_CACHE.
+    if ($path.StartsWith($env:RUNNER_TOOL_CACHE)) {
+        if (Test-Path "$path\python.exe") {
+            $paths += $path
+        }
+    }
+}
+
+# Sort the paths, ensure each path is unique, and create the output result.
+$result = (
+    $paths `
+    | Sort-Object `
+    | Get-Unique
+) -join ";"
+
+# Output path information.
+# This must be the final line because it will be automatically transformed to:
+#
+#     Write-Output "python-identifiers=$result" > "$env:GITHUB_OUTPUT"
+#
+Write-Output "python-identifiers=$result"
diff --git a/src/detect_pythons/detector.sh b/src/detect_pythons/detector.sh
new file mode 100644
index 0000000..243ac26
--- /dev/null
+++ b/src/detect_pythons/detector.sh
@@ -0,0 +1,79 @@
+# Do not modify the Python code below.
+# It is copied from 'identify.py' by a pre-commit hook.
+python_code=$(
+cat <<'identify.py_SOURCE_CODE'
+from __future__ import print_function
+
+import sysconfig
+
+
+def main():
+    ext_suffix = sysconfig.get_config_var("EXT_SUFFIX")
+    if ext_suffix is not None:
+        print(ext_suffix)
+    else:
+        # Python 2.7 on GitHub macOS runners
+        import platform
+
+        print(
+            "." + platform.python_implementation().lower(),
+            sysconfig.get_config_var("py_version_nodot"),
+            sysconfig.get_config_var("MACHDEP"),
+            sep="-",
+        )
+
+
+if __name__ == "__main__":
+    main()
+identify.py_SOURCE_CODE
+)
+
+# Search paths in $PATH for Python interpreters.
+IFS=: read -r -a all_paths <<< "$PATH"
+
+# Detect Python interpreters.
+paths=()
+for path in "${all_paths[@]}"; do
+    # Interpreters in RUNNER_TOOL_CACHE have directory names that include:
+    #
+    # * The implementation (like "Python" or "PyPy")
+    # * A version (like "3.10.12")
+    # * The architecture (like "x64")
+    #
+    # In such cases, the path can be used as the identifier.
+    if [[ "${path/#${RUNNER_TOOL_CACHE}/}" != "${path}" ]]; then
+        # Check for bin/python first;
+        # this results in duplicate paths which are later removed.
+        if [[ -x "${path}/bin/python" ]]; then
+            paths+=("${path}/bin")
+        elif [[ -x "${path}/python" ]]; then
+            paths+=("${path}")
+        fi
+    else
+        # System Pythons (e.g. /usr/bin/python) have nothing unique in the path.
+        # In such cases, it's necessary to run the executable to get something unique.
+        if [[ -x "${path}/python" ]]; then
+            paths+=("${path}")
+            paths+=("$(echo "${python_code}" | "${path}/python" -)")
+        fi
+    fi
+done
+
+# Sort the paths, ensure each path is unique, and create the output result.
+result="$(
+    echo "${paths[*]}" \
+    | tr ' ' '\n' \
+    | sort \
+    | uniq \
+    | tr '\n' ':'
+)"
+
+# Trim trailing colons.
+result="${result%:}"
+
+# Output path information.
+# This must be the final line because it will be automatically transformed to:
+#
+#     echo "python-identifiers=${result}" > "$GITHUB_OUTPUT"
+#
+echo "python-identifiers=${result}"
diff --git a/src/detect_pythons/identify.py b/src/detect_pythons/identify.py
new file mode 100644
index 0000000..ec0541d
--- /dev/null
+++ b/src/detect_pythons/identify.py
@@ -0,0 +1,23 @@
+from __future__ import print_function
+
+import sysconfig
+
+
+def main():
+    ext_suffix = sysconfig.get_config_var("EXT_SUFFIX")
+    if ext_suffix is not None:
+        print(ext_suffix)
+    else:
+        # Python 2.7 on GitHub macOS runners
+        import platform
+
+        print(
+            "." + platform.python_implementation().lower(),
+            sysconfig.get_config_var("py_version_nodot"),
+            sysconfig.get_config_var("MACHDEP"),
+            sep="-",
+        )
+
+
+if __name__ == "__main__":
+    main()
diff --git a/src/detect_pythons/sync_detector_code.py b/src/detect_pythons/sync_detector_code.py
new file mode 100644
index 0000000..bd49107
--- /dev/null
+++ b/src/detect_pythons/sync_detector_code.py
@@ -0,0 +1,67 @@
+import pathlib
+import sys
+import textwrap
+
+FILES_NOT_MODIFIED = 0
+FILES_MODIFIED = 1
+
+DETECTOR_SH = (pathlib.Path(__file__).parent / "detector.sh").resolve()
+DETECTOR_PS1 = (pathlib.Path(__file__).parent / "detector.ps1").resolve()
+ACTION_YML = (pathlib.Path(__file__).parent / "../../action.yml").resolve()
+
+
+def sync(path: pathlib.Path) -> int:
+    # Verify the paths are acceptable.
+    if path != DETECTOR_SH and path != DETECTOR_PS1:
+        print(f"{path} is not an acceptable file path.")
+        return FILES_NOT_MODIFIED
+
+    code = path.read_text().strip()
+
+    # Prevent YAML syntax errors caused by shared comment syntax.
+    if code.lstrip().startswith("#"):
+        if path == DETECTOR_SH:
+            code = "true > /dev/null  # No-op to prevent YAML syntax errors.\n" + code
+        else:  # path == DETECTOR_PS1
+            code = "$true | Out-Null  # No-op to prevent YAML syntax errors.\n" + code
+
+    # Redirect outputs to GITHUB_OUTPUT.
+    if path == DETECTOR_SH:
+        code += ' > "$GITHUB_OUTPUT"'
+    else:  # path == DETECTOR_PS1
+        code += ' > "$env:GITHUB_OUTPUT"'
+
+    # Determine the text boundaries of the source code in 'action.yml'.
+    yaml = ACTION_YML.read_text()
+    start_line = f"# START: {path.name}\n"
+    end_line = f"# END: {path.name}"
+    start = yaml.find(start_line) + len(start_line)
+    end = yaml.rfind("\n", start, yaml.find(end_line, start))
+    indent = yaml.find("run:", start) - start
+
+    # Prepare the code for injection.
+    block = textwrap.indent("run: |\n" + textwrap.indent(code, " " * 2), " " * indent)
+
+    # Inject the source code and determine if 'action.yml' needs to be overwritten.
+    new_yaml = yaml[:start] + block + yaml[end:]
+    if new_yaml != yaml:
+        ACTION_YML.write_text(new_yaml, newline="\n")
+        return FILES_MODIFIED
+
+    return FILES_NOT_MODIFIED
+
+
+def main():
+    if len(sys.argv) < 2:
+        print("The path to 'detector.sh' or 'detector.ps1' must be provided.")
+        sys.exit(FILES_NOT_MODIFIED)
+
+    rc = FILES_NOT_MODIFIED
+    for argument in sys.argv[1:]:
+        rc |= sync(pathlib.Path(argument).resolve())
+
+    sys.exit(rc)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/src/detect_pythons/sync_identify_code.py b/src/detect_pythons/sync_identify_code.py
new file mode 100644
index 0000000..5b8ee82
--- /dev/null
+++ b/src/detect_pythons/sync_identify_code.py
@@ -0,0 +1,44 @@
+import pathlib
+import sys
+
+FILES_NOT_MODIFIED = 0
+FILES_MODIFIED = 1
+
+IDENTIFY_PY = (pathlib.Path(__file__).parent / "identify.py").resolve()
+DETECTOR_SH = (pathlib.Path(__file__).parent / "detector.sh").resolve()
+
+
+def sync(path: pathlib.Path) -> int:
+    # Verify the paths are acceptable.
+    if path != IDENTIFY_PY:
+        print(f"{path} is not an acceptable file path.")
+        return FILES_NOT_MODIFIED
+
+    code = path.read_text().strip()
+
+    # Determine the text boundaries of the source code in 'action.yml'.
+    sh = DETECTOR_SH.read_text()
+    tag = f"{IDENTIFY_PY.name}_SOURCE_CODE"
+    start = sh.find("\n", sh.find(tag)) + 1
+    end = sh.rfind("\n", start, sh.find(tag, start))
+
+    # Inject the source code and determine if 'action.yml' needs to be overwritten.
+    new_sh = sh[:start] + code + sh[end:]
+    if new_sh != sh:
+        DETECTOR_SH.write_text(new_sh, newline="\n")
+        return FILES_MODIFIED
+
+    return FILES_NOT_MODIFIED
+
+
+def main():
+    if len(sys.argv) < 2:
+        print(f"The path to a modified '{IDENTIFY_PY.name}' must be provided.")
+        sys.exit(FILES_NOT_MODIFIED)
+
+    rc = sync(pathlib.Path(sys.argv[-1]).resolve())
+    sys.exit(rc)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/src/detect_pythons/sync_readme_example.py b/src/detect_pythons/sync_readme_example.py
new file mode 100644
index 0000000..d3e558c
--- /dev/null
+++ b/src/detect_pythons/sync_readme_example.py
@@ -0,0 +1,46 @@
+import pathlib
+import sys
+import textwrap
+
+FILES_NOT_MODIFIED = False
+FILES_MODIFIED = True
+
+ROOT = pathlib.Path(__file__).parent.parent.parent
+EXAMPLE_YAML = (ROOT / ".github/workflows/readme_example.yaml").resolve()
+README_RST = (ROOT / "README.rst").resolve()
+
+
+def sync() -> bool:
+    # Extract the YAML example to embed in the README.
+    yaml = EXAMPLE_YAML.read_text(encoding="utf-8")
+    start_line = "# START_README_EXAMPLE_BLOCK\n"
+    end_line = "# END_README_EXAMPLE_BLOCK"
+    start = yaml.find(start_line) + len(start_line)
+    end = yaml.rfind("\n", start, yaml.find(end_line, start))
+    example = textwrap.dedent(yaml[start:end])
+
+    # Prepare the example for injection.
+    block = "..  code-block:: yaml\n\n" + textwrap.indent(example, " " * 4)
+
+    # Determine the text boundaries of the source code in the README.
+    rst = README_RST.read_text()
+    start_line = "..  START_EXAMPLE_YAML_BLOCK\n"
+    end_line = "..  END_EXAMPLE_YAML_BLOCK"
+    start = rst.find(start_line) + len(start_line)
+    end = rst.rfind("\n", start, rst.find(end_line, start))
+
+    # Inject the example and determine if the README needs to be overwritten.
+    new_rst = rst[:start] + block + rst[end:]
+    if new_rst != rst:
+        README_RST.write_text(new_rst, newline="\n")
+        return FILES_MODIFIED
+
+    return FILES_NOT_MODIFIED
+
+
+def main():
+    sys.exit(sync())
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..8dd399a
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,3 @@
+[flake8]
+max-line-length = 88
+extend-ignore = E203