diff --git a/packages/create-python-app-core/README.md b/packages/create-python-app-core/README.md
index 4e8427e..291ea16 100644
--- a/packages/create-python-app-core/README.md
+++ b/packages/create-python-app-core/README.md
@@ -1,3 +1,15 @@
 # create-python-app-core
 
-Programmatic scaffolding engine (stub). Consumed by `create-awesome-python-app`.
+Programmatic scaffolding engine behind Create Awesome Python App.
+
+```python
+from create_python_app_core import (
+    create_python_app,
+    check_python_version,
+    check_for_latest_version,
+    print_env_info,
+    CPA_USER_AGENT,
+)
+```
+
+Requires **Python >= 3.12**.
diff --git a/packages/create-python-app-core/pyproject.toml b/packages/create-python-app-core/pyproject.toml
index d2087b6..ee8b00a 100644
--- a/packages/create-python-app-core/pyproject.toml
+++ b/packages/create-python-app-core/pyproject.toml
@@ -4,7 +4,9 @@ version = "0.0.0"
 description = "Scaffolding engine for Create Awesome Python App (stub)"
 readme = "README.md"
 requires-python = ">=3.12"
-dependencies = []
+dependencies = [
+    "packaging>=24.0",
+]
 
 [build-system]
 requires = ["hatchling"]
diff --git a/packages/create-python-app-core/src/create_python_app_core/__init__.py b/packages/create-python-app-core/src/create_python_app_core/__init__.py
index bbb407c..f18acff 100644
--- a/packages/create-python-app-core/src/create_python_app_core/__init__.py
+++ b/packages/create-python-app-core/src/create_python_app_core/__init__.py
@@ -1,3 +1,21 @@
-"""Scaffolding engine for Create Awesome Python App."""
+"""Programmatic scaffolding engine for Create Awesome Python App."""
 
-__version__ = "0.0.0"
+from __future__ import annotations
+
+from create_python_app_core._version import __version__
+from create_python_app_core.api import (
+    CPA_USER_AGENT,
+    check_for_latest_version,
+    check_python_version,
+    create_python_app,
+    print_env_info,
+)
+
+__all__ = [
+    "__version__",
+    "CPA_USER_AGENT",
+    "check_for_latest_version",
+    "check_python_version",
+    "create_python_app",
+    "print_env_info",
+]
diff --git a/packages/create-python-app-core/src/create_python_app_core/_version.py b/packages/create-python-app-core/src/create_python_app_core/_version.py
new file mode 100644
index 0000000..6c8e6b9
--- /dev/null
+++ b/packages/create-python-app-core/src/create_python_app_core/_version.py
@@ -0,0 +1 @@
+__version__ = "0.0.0"
diff --git a/packages/create-python-app-core/src/create_python_app_core/api.py b/packages/create-python-app-core/src/create_python_app_core/api.py
new file mode 100644
index 0000000..299cf2f
--- /dev/null
+++ b/packages/create-python-app-core/src/create_python_app_core/api.py
@@ -0,0 +1,59 @@
+"""Public API surface (mirrors @create-node-app/core index exports)."""
+
+from __future__ import annotations
+
+import sys
+from collections.abc import Awaitable, Callable
+from typing import Any
+
+from create_python_app_core._version import __version__
+
+CPA_USER_AGENT = (
+    f"create-python-app-core/{__version__} "
+    "(https://github.com/Create-Python-App/create-python-app)"
+)
+
+
+def check_python_version(required: str, package_name: str) -> None:
+    """Exit if the running interpreter does not satisfy *required* (PEP 440)."""
+    from packaging.specifiers import SpecifierSet
+    from packaging.version import Version
+
+    current = Version(".".join(map(str, sys.version_info[:3])))
+    if current not in SpecifierSet(required):
+        print(
+            f"You are running Python {current}.\n"
+            f"{package_name} requires Python {required}.\n"
+            "Please update your version of Python.",
+            file=sys.stderr,
+        )
+        raise SystemExit(1)
+
+
+async def check_for_latest_version(package_name: str) -> str | None:
+    """Fetch latest version from PyPI. Returns None on failure."""
+    # Implemented fully in #31; stub returns None until then.
+    _ = package_name
+    return None
+
+
+def print_env_info() -> None:
+    """Print environment info then exit. Full implementation in #30."""
+    print(f"create-python-app-core {__version__}")
+    print(f"Python {sys.version}")
+    raise SystemExit(0)
+
+
+async def create_python_app(
+    project_directory: str,
+    options: dict[str, Any],
+    transform_options: Callable[[dict[str, Any]], Awaitable[dict[str, Any]]]
+    | None = None,
+) -> None:
+    """Scaffold a project. Full installer lands in #29."""
+    if transform_options is not None:
+        options = await transform_options(options)
+    raise NotImplementedError(
+        "create_python_app installer not implemented yet — see #29 "
+        f"(project={project_directory!r}, options_keys={list(options)})"
+    )
diff --git a/packages/create-python-app-core/tests/test_api.py b/packages/create-python-app-core/tests/test_api.py
new file mode 100644
index 0000000..6c4e242
--- /dev/null
+++ b/packages/create-python-app-core/tests/test_api.py
@@ -0,0 +1,11 @@
+import pytest
+from create_python_app_core import check_python_version
+
+
+def test_check_python_version_accepts_current() -> None:
+    check_python_version(">=3.12", "create-python-app-core")
+
+
+def test_check_python_version_rejects_impossible() -> None:
+    with pytest.raises(SystemExit):
+        check_python_version(">=99.0", "create-python-app-core")
diff --git a/packages/create-python-app-core/tests/test_version.py b/packages/create-python-app-core/tests/test_version.py
index 45843ee..f513cfc 100644
--- a/packages/create-python-app-core/tests/test_version.py
+++ b/packages/create-python-app-core/tests/test_version.py
@@ -1,5 +1,10 @@
-from create_python_app_core import __version__
+from create_python_app_core import CPA_USER_AGENT, __version__
 
 
 def test_version_is_semver_stub() -> None:
     assert __version__ == "0.0.0"
+
+
+def test_user_agent_contains_version() -> None:
+    assert __version__ in CPA_USER_AGENT
+    assert "create-python-app-core" in CPA_USER_AGENT
diff --git a/uv.lock b/uv.lock
index 1b44797..aa3c3b0 100644
--- a/uv.lock
+++ b/uv.lock
@@ -119,6 +119,12 @@ requires-dist = [{ name = "create-python-app-core", editable = "packages/create-
 name = "create-python-app-core"
 version = "0.0.0"
 source = { editable = "packages/create-python-app-core" }
+dependencies = [
+    { name = "packaging" },
+]
+
+[package.metadata]
+requires-dist = [{ name = "packaging", specifier = ">=24.0" }]
 
 [[package]]
 name = "distlib"