diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
new file mode 100644
index 0000000..48142fd
--- /dev/null
+++ b/.github/workflows/test.yaml
@@ -0,0 +1,34 @@
+name: "Test"
+
+on:
+  push:
+      branches:
+        - "main"
+
+jobs:
+  test-linux:
+    name: "Test on ${{ matrix.config.os-name }}"
+    runs-on: "${{ matrix.config.runner }}"
+    strategy:
+      matrix:
+        config:
+          - os-name: "Linux"
+            runner: "ubuntu-latest"
+            test-label: "ci-test-linux"
+          - os-name: "macOS"
+            runner: "macos-latest"
+            test-label: "ci-test-macos"
+          - os-name: "Windows"
+            runner: "windows-latest"
+            test-label: "ci-test-windows"
+      fail-fast: false
+
+    steps:
+      - name: "Use it!"
+        id: "finder"
+        uses: "kurtmckee/setup-python-version-detector@main"
+
+      - name: "Print it!"
+        shell: "bash"
+        run: |
+          echo '${{ steps.finder.outputs.python-identifiers }}'
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..bee8a64
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+__pycache__
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..ae54e3e
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,31 @@
+ci:
+  autoupdate_schedule: "monthly"
+
+repos:
+  - repo: "https://github.com/pre-commit/pre-commit-hooks"
+    rev: "v4.5.0"
+    hooks:
+      - id: "trailing-whitespace"
+      - id: "end-of-file-fixer"
+      - id: "check-yaml"
+      - id: "check-added-large-files"
+
+  - repo: "https://github.com/python-jsonschema/check-jsonschema"
+    rev: "0.27.0"
+    hooks:
+      - id: "check-github-workflows"
+      - id: "check-dependabot"
+
+  - repo: "local"
+    hooks:
+      - id: "sync-identify-code"
+        name: "Synchronize identify.py source code into 'finder.sh'"
+        language: "python"
+        entry: "python src/python_cache_buster/sync_identify_code.py"
+        files: "^src/python_cache_buster/identify.py$"
+
+      - id: "sync-finder-code"
+        name: "Synchronize finder source code into 'action.yml'"
+        language: "python"
+        entry: "python src/python_cache_buster/sync_finder_code.py"
+        files: "^src/python_cache_buster/finder.*$"
diff --git a/README.rst b/README.rst
new file mode 100644
index 0000000..3171e9e
--- /dev/null
+++ b/README.rst
@@ -0,0 +1,6 @@
+Identify Python interpreters
+############################
+
+*Robust cache-busting based on Python implementations, architectures, and versions.*
+
+----
diff --git a/TODO.rst b/TODO.rst
new file mode 100644
index 0000000..8762a8e
--- /dev/null
+++ b/TODO.rst
@@ -0,0 +1,8 @@
+*   Add shellcheck pre-commit hook for finder.sh
+*   Add a Powershell syntax checker for finder.ps1
+*   Expand README
+*   Create ``releases`` branch for tagging and such
+*   Add pre-commit hook to check README against latest tagged SHA
+*   Rename repo...maybe ``python-cache-buster``
+*   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..9b9bfd9
--- /dev/null
+++ b/action.yml
@@ -0,0 +1,143 @@
+name: "Identify installed Python interpreters"
+description: |
+  Find 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 minor versions.
+
+  Only Python interpreters named "python" in the $PATH will be found.
+
+outputs:
+  python-identifiers:
+    description: |
+      A string of sorted Python identifiers.
+
+      In most cases the identifiers will be paths,
+      but for system Pythons, 'sysconfig.get_config_var("EXT_SUFFIX")' will be included.
+
+      The string will be separated by OS-specific PATH separators;
+      ":" is used on Linux and macOS, and ";" is used on Windows.
+    value: "${{ steps.final-step.outputs.python-identifiers }}"
+
+runs:
+  using: "composite"
+  steps:
+    - name: "Find Pythons on Linux / macOS"
+      id: "linux"
+      if: "runner.os != 'windows'"
+      shell: "bash"
+      # Do not edit the 'run' code below.
+      # It is copied from 'finder.sh' by a pre-commit hook.
+      # START: finder.sh
+      run: |
+        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"
+
+        # Find 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 "${path}/python" ]]; then
+                    paths+=("$(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="${result%:}"
+
+        # Output path information.
+        echo "python-identifiers=${result}" > "$GITHUB_OUTPUT"
+      # END: finder.sh
+
+    - name: "Find Pythons on Windows"
+      id: "windows"
+      if: "runner.os == 'windows'"
+      shell: "powershell"
+      # Do not edit the 'run' code below.
+      # It is copied from 'finder.ps1' by a pre-commit hook.
+      # START: finder.ps1
+      run: |
+        $true | Out-Null  # No-op to prevent YAML syntax errors.
+        # Search paths in $PATH for Python interpreters.
+        $all_paths = $env:PATH -split ";"
+
+        # Find 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 = (
+            $paths `
+            | Sort-Object `
+            | Get-Unique
+        ) -join ";"
+
+        # Output path information.
+        Write-Output "python-identifiers=$result" > "$env:GITHUB_OUTPUT"
+      # END: finder.ps1
+
+    - name: "Output"
+      id: "final-step"
+      shell: "bash"
+      run: |
+        echo 'python-identifiers=${{ steps.linux.outputs.python-identifiers }}${{ steps.windows.outputs.python-identifiers }}' > "$GITHUB_OUTPUT"
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..485c298
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,20 @@
+[tool.poetry]
+name = "python_cache_buster"
+version = "1.0.0"
+description = ""
+authors = ["Kurt McKee <contactme@kurtmckee.org>"]
+license = "MIT"
+readme = "README.rst"
+
+[tool.poetry.scripts]
+identify = "python_cache_buster.identify:main"
+sync-finder-code = "python_cache_buster.sync_finder_code:main"
+sync-identify-code = "python_cache_buster.sync_identify_code:main"
+
+[tool.poetry.dependencies]
+python = ">=3.8"
+
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"
diff --git a/src/python_cache_buster/__init__.py b/src/python_cache_buster/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/python_cache_buster/finder.ps1 b/src/python_cache_buster/finder.ps1
new file mode 100644
index 0000000..3cd97be
--- /dev/null
+++ b/src/python_cache_buster/finder.ps1
@@ -0,0 +1,23 @@
+# Search paths in $PATH for Python interpreters.
+$all_paths = $env:PATH -split ";"
+
+# Find Python interpreters.
+$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 = (
+    $paths `
+    | Sort-Object `
+    | Get-Unique
+) -join ";"
+
+# Output path information.
+Write-Output "python-identifiers=$result"
diff --git a/src/python_cache_buster/finder.sh b/src/python_cache_buster/finder.sh
new file mode 100644
index 0000000..5375bbb
--- /dev/null
+++ b/src/python_cache_buster/finder.sh
@@ -0,0 +1,71 @@
+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"
+
+# Find 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 "${path}/python" ]]; then
+            paths+=("$(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="${result%:}"
+
+# Output path information.
+echo "python-identifiers=${result}"
diff --git a/src/python_cache_buster/identify.py b/src/python_cache_buster/identify.py
new file mode 100644
index 0000000..afe601a
--- /dev/null
+++ b/src/python_cache_buster/identify.py
@@ -0,0 +1,22 @@
+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/python_cache_buster/sync_finder_code.py b/src/python_cache_buster/sync_finder_code.py
new file mode 100644
index 0000000..f14152f
--- /dev/null
+++ b/src/python_cache_buster/sync_finder_code.py
@@ -0,0 +1,67 @@
+import sys
+import pathlib
+import textwrap
+
+FILES_NOT_MODIFIED = 0
+FILES_MODIFIED = 1
+
+FINDER_SH = (pathlib.Path(__file__).parent / "finder.sh").resolve()
+FINDER_PS1 = (pathlib.Path(__file__).parent / "finder.ps1").resolve()
+ACTION_YML = (pathlib.Path(__file__).parent / "../../action.yml").resolve()
+
+
+def sync(path: pathlib.Path) -> int:
+    # Verify the paths are acceptable.
+    if path != FINDER_SH and path != FINDER_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 == FINDER_SH:
+            code = "true > /dev/null  # No-op to prevent YAML syntax errors.\n" + code
+        else:  # path == FINDER_PS1
+            code = "$true | Out-Null  # No-op to prevent YAML syntax errors.\n" + code
+
+    # Redirect outputs to GITHUB_OUTPUT.
+    if path == FINDER_SH:
+        code += ' > "$GITHUB_OUTPUT"'
+    else:  # path == FINDER_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)
+        return FILES_MODIFIED
+
+    return FILES_NOT_MODIFIED
+
+
+def main():
+    if len(sys.argv) < 2:
+        print("The path to a modified 'finder.sh' or 'finder.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/python_cache_buster/sync_identify_code.py b/src/python_cache_buster/sync_identify_code.py
new file mode 100644
index 0000000..6154d38
--- /dev/null
+++ b/src/python_cache_buster/sync_identify_code.py
@@ -0,0 +1,44 @@
+import sys
+import pathlib
+
+FILES_NOT_MODIFIED = 0
+FILES_MODIFIED = 1
+
+IDENTIFY_PY = (pathlib.Path(__file__).parent / "identify.py").resolve()
+FINDER_SH = (pathlib.Path(__file__).parent / "finder.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 = FINDER_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:
+        FINDER_SH.write_text(new_sh)
+        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()