diff --git a/Makefile b/Makefile
index 3355b8c..e0ce73d 100644
--- a/Makefile
+++ b/Makefile
@@ -18,6 +18,7 @@ check-fmt: ## Verify template test formatting
 
 lint: ## Run template test lint checks
 	$(UV) ruff check tests/
+	$(UV) --with interrogate interrogate --fail-under 100 tests/
 
 typecheck: ## Run template test type checks
 	$(UV) --with pytest --with pytest-copier --with pyyaml --with syrupy --with make-parser ty check tests/
diff --git a/README.md b/README.md
index f4db656..6818522 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,8 @@ Run `copier copy` and answer the prompts to generate a project.
 The test suite relies on the `pytest-copier` plugin and renders generated
 projects that run Ruff, Pylint via a PyPy-backed runner, `ty`, pytest, and, when
 the Rust extension is enabled, Clippy, Whitaker, and nextest-aware Rust tests.
+Generated Python linting also runs Interrogate as a 100% docstring-coverage
+gate.
 
 Run the parent template tests through the repository `Makefile`. Run
 `make help` to list the available parent Makefile targets. Parent gates include
@@ -30,8 +32,9 @@ when `act` and Docker are available. Parent repository CI runs this mode in a
 separate act-validation workflow so rendered in-template GitHub workflows do not
 hold up the normal template test workflow.
 
-Generated projects install and run their own tooling, including Ruff, Pylint via
-PyPy, `ty`, pytest, and, when Rust is enabled, Clippy, Whitaker, and nextest.
+Generated projects install and run their own tooling, including Ruff,
+Interrogate, Pylint via PyPy, `ty`, pytest, and, when Rust is enabled, Clippy,
+Whitaker, and nextest.
 
 You can also run `scripts/setup_test_deps.sh` to install parent test
 dependencies into the current Python environment manually.
@@ -54,6 +57,7 @@ flowchart LR
     All --> Test[test]
 
     Lint --> RuffCheck[ruff check]
+    Lint --> Interrogate[interrogate --fail-under 100]
     Lint --> PylintPyPy[pylint-pypy via PyPy]
     Typecheck --> TyCheck[ty check]
     Audit --> PipAudit[pip-audit]
diff --git a/docs/adr-001-template-quality-gates.md b/docs/adr-001-template-quality-gates.md
index d82ddbf..2905fd7 100644
--- a/docs/adr-001-template-quality-gates.md
+++ b/docs/adr-001-template-quality-gates.md
@@ -16,7 +16,7 @@ failures are predictable.
 Generated projects use `make all` as the public aggregate gate. The `lint`
 target delegates to language-specific targets:
 
-- `lint-python` runs Ruff and Pylint through the PyPy-backed runner.
+- `lint-python` runs Ruff, Interrogate (`--fail-under 100`), and Pylint through the PyPy-backed runner.
 - `lint-rust` is rendered only when `use_rust` is enabled and runs rustdoc,
   Clippy, and Whitaker.
 
diff --git a/docs/developers-guide.md b/docs/developers-guide.md
index 1c91f98..0f9869b 100644
--- a/docs/developers-guide.md
+++ b/docs/developers-guide.md
@@ -12,7 +12,8 @@ template itself.
 - `make help` — lists all `##`-annotated targets.
 - `make check-fmt` — runs Ruff formatting checks against the parent template
   test suite.
-- `make lint` — runs Ruff lint checks against the parent template test suite.
+- `make lint` — runs Ruff lint checks and `interrogate --fail-under 100` against
+  the `tests/` directory in the parent template test suite.
 - `make typecheck` — runs `ty check` against the parent template test suite,
   supplying the test dependencies through `uvx`.
 - `make test` — runs the template test suite via `uvx`, supplying
@@ -50,7 +51,9 @@ runs `cargo audit` in the Rust extension crate.
 
 The generated lint targets are split by language:
 
-- `lint-python` runs Ruff and Pylint via the pinned PyPy-backed runner.
+- `lint-python` runs Ruff, `interrogate --fail-under 100` for 100% docstring
+  coverage across `$(PYTHON_TARGETS)`, and Pylint via the pinned PyPy-backed
+  runner.
 - `lint-rust` exists only when `use_rust` is enabled and runs rustdoc, Clippy,
   and Whitaker.
 - `lint` delegates to the applicable language-specific targets.
diff --git a/template/AGENTS.md.jinja b/template/AGENTS.md.jinja
index bb6c5e4..220f1e9 100644
--- a/template/AGENTS.md.jinja
+++ b/template/AGENTS.md.jinja
@@ -81,8 +81,9 @@
     - `make check-fmt` runs Ruff formatting checks with
       `ruff format --check $(PYTHON_TARGETS)`.
     - `make lint` runs `make lint-python`; `make lint-python` runs
-      `ruff check $(PYTHON_TARGETS)` and the PyPy-backed Pylint runner against
-      `$(PYLINT_TARGETS)`.
+      `ruff check $(PYTHON_TARGETS)`, enforces 100% docstring coverage with
+      `interrogate --fail-under 100 $(PYTHON_TARGETS)`, and runs the
+      PyPy-backed Pylint runner against `$(PYLINT_TARGETS)`.
     - `make typecheck` runs `ty check $(PYTHON_TARGETS)`.
     - `make test` runs `pytest -v -n $(PYTEST_XDIST_WORKERS)` and honours
       `WITH_ACT=1` through `RUN_ACT_VALIDATION=1`.
diff --git a/template/Makefile.jinja b/template/Makefile.jinja
index 3882c4e..e73647f 100644
--- a/template/Makefile.jinja
+++ b/template/Makefile.jinja
@@ -136,6 +136,7 @@ lint: lint-python{% if use_rust %} lint-rust{% endif %} ## Run linters
 
 lint-python: build ## Run Python linters
 	$(UV_ENV) $(UV) run ruff check $(PYTHON_TARGETS)
+	$(UV_ENV) $(UV) run interrogate --fail-under 100 $(PYTHON_TARGETS)
 	$(PYLINT) $(PYLINT_TARGETS)
 {% if use_rust %}
 
diff --git a/template/docs/developers-guide.md b/template/docs/developers-guide.md
index 5723a94..98ff017 100644
--- a/template/docs/developers-guide.md
+++ b/template/docs/developers-guide.md
@@ -9,6 +9,9 @@ The public entrypoint for formatting, linting, typechecking, and tests is
 failure, and changes should be reconciled with the aggregate gate before being
 considered complete.
 
+`make lint` runs Ruff, `interrogate --fail-under 100 $(PYTHON_TARGETS)` for
+100% docstring coverage across `$(PYTHON_TARGETS)`, and Pylint.
+
 Run `make audit` as the dependency vulnerability gate. It runs `pip-audit` for
 Python dependencies, and Rust-enabled projects also run `cargo audit` from the
 `rust_extension` crate directory.
@@ -32,10 +35,12 @@ actions under `.github/`.
 
 - `.github/workflows/ci.yml` runs on pushes to `main` and on pull requests. It
   sets up Python 3.13, installs `uv`, validates the generated `Makefile` with
-  `mbake`, runs `make build`, `make check-fmt`, `make lint`, `make typecheck`,
-  and `make audit`, then delegates coverage generation to the shared coverage
-  action. When the Rust extension is enabled, it also sets up Rust, installs
-  Rust lint and test tools, and passes `rust_extension/Cargo.toml` to coverage.
+  `mbake`, runs `make build`, `make check-fmt`,
+  `make lint` (Ruff + `interrogate --fail-under 100 $(PYTHON_TARGETS)` + Pylint), `make
+  typecheck`, and `make audit`, then delegates coverage generation to the shared
+  coverage action. When the Rust extension is enabled, it also sets up Rust,
+  installs Rust lint and test tools, and passes `rust_extension/Cargo.toml` to
+  coverage.
 - `.github/workflows/act-validation.yml` runs rendered workflow validation in a
   separate workflow. It installs `act`, checks Docker availability, and runs
   `make test WITH_ACT=1` outside the coverage path.
diff --git a/template/docs/users-guide.md.jinja b/template/docs/users-guide.md.jinja
index 2b9e639..ab295e9 100644
--- a/template/docs/users-guide.md.jinja
+++ b/template/docs/users-guide.md.jinja
@@ -14,8 +14,10 @@ these targets in order:
 - `test`: run pytest and, when Rust is enabled, Rust tests.
 - `audit`: run `pip-audit` and, when Rust is enabled, `cargo audit`.
 
-The `lint-python` target runs Ruff followed by Pylint via a PyPy-backed runner.
-The Pylint runner is installed through `uv tool run` from the pinned
+The `lint-python` target runs Ruff, then Interrogate with
+`interrogate --fail-under 100 $(PYTHON_TARGETS)` to enforce 100% docstring
+coverage for the Python targets, then Pylint via a PyPy-backed runner. The Pylint
+runner is installed through `uv tool run` from the pinned
 `pylint-pypy-shim` repository.
 
 Pytest discovery is limited to the top-level `tests/` tree. Keep generated
diff --git a/template/pyproject.toml.jinja b/template/pyproject.toml.jinja
index 6689f87..9f2fddf 100644
--- a/template/pyproject.toml.jinja
+++ b/template/pyproject.toml.jinja
@@ -10,6 +10,7 @@ dependencies = []
 [dependency-groups]
 dev = [
     "pytest",
+    "interrogate",
     "pip-audit",
     "ruff",
     "pyright",
diff --git a/template/{% if use_rust %}rust_extension{% endif %}/Cargo.toml.jinja b/template/{% if use_rust %}rust_extension{% endif %}/Cargo.toml.jinja
index a3d8e7d..588c21e 100644
--- a/template/{% if use_rust %}rust_extension{% endif %}/Cargo.toml.jinja	
+++ b/template/{% if use_rust %}rust_extension{% endif %}/Cargo.toml.jinja	
@@ -8,7 +8,7 @@ name = "_{{ package_name }}_rs"
 crate-type = ["cdylib", "rlib"]
 
 [dependencies]
-pyo3 = { version = "0.28.3", features = ["extension-module"] }
+pyo3 = { version = "0.29.0", features = ["extension-module"] }
 
 [lints.clippy]
 pedantic = { level = "warn", priority = -1 }
diff --git a/tests/helpers/agents_contracts.py b/tests/helpers/agents_contracts.py
index 947108b..b1e321a 100644
--- a/tests/helpers/agents_contracts.py
+++ b/tests/helpers/agents_contracts.py
@@ -98,7 +98,9 @@ def _assert_documented_command_flags(
         ],
         "lint-python": [
             ("AGENTS.md", "ruff check $(PYTHON_TARGETS)"),
+            ("AGENTS.md", "interrogate --fail-under 100 $(PYTHON_TARGETS)"),
             ("Makefile", f"ruff check {python_targets}"),
+            ("Makefile", f"interrogate --fail-under 100 {python_targets}"),
         ],
         "typecheck": [
             ("AGENTS.md", "ty check $(PYTHON_TARGETS)"),
diff --git a/tests/helpers/makefile_contracts.py b/tests/helpers/makefile_contracts.py
index 9e579c9..8157f0f 100644
--- a/tests/helpers/makefile_contracts.py
+++ b/tests/helpers/makefile_contracts.py
@@ -56,6 +56,7 @@ def _parse_makefile_rules(makefile: str) -> dict[str, list[str]]:
     }
 
     def normalise_target(match: re.Match[str]) -> str:
+        """Replace hyphenated target names with parser-compatible aliases."""
         target = match.group(1)
         return normalised_targets.get(target, target) + ":"
 
@@ -104,6 +105,9 @@ def _assert_makefile_contracts(*, makefile: str, use_rust: bool) -> None:
     assert "$(UV_ENV) $(UV) run pip-audit" in makefile, (
         "expected generated audit target to run pip-audit"
     )
+    assert "$(UV_ENV) $(UV) run interrogate --fail-under 100" in makefile, (
+        "expected generated lint target to enforce docstring coverage"
+    )
     if use_rust:
         assert "TEST_CMD :=" in makefile, (
             "expected Rust variant to select nextest or cargo test"
diff --git a/tests/helpers/pyproject_contracts.py b/tests/helpers/pyproject_contracts.py
index 7e32024..4425daf 100644
--- a/tests/helpers/pyproject_contracts.py
+++ b/tests/helpers/pyproject_contracts.py
@@ -32,7 +32,16 @@ def _assert_pyproject_contracts(
     assert isinstance(dev_dependencies, list), (
         "expected generated pyproject.toml to include a dev dependency group"
     )
-    for dependency in ["pytest", "pip-audit", "ruff", "pyright", "ty", "pytest-xdist"]:
+    for dependency in [
+        "pytest",
+        "interrogate",
+        "pip-audit",
+        "ruff",
+        "pyright",
+        "ty",
+        "pytest-timeout",
+        "pytest-xdist",
+    ]:
         assert dependency in dev_dependencies, (
             f"expected generated dev dependencies to include {dependency}"
         )
diff --git a/tests/test_github_actions_integration.py b/tests/test_github_actions_integration.py
index 0a840ad..3bb15a1 100644
--- a/tests/test_github_actions_integration.py
+++ b/tests/test_github_actions_integration.py
@@ -173,6 +173,7 @@ def test_run_act_forwards_only_explicit_act_github_token(
     captured_command: list[str] = []
 
     def fake_run(command: list[str], **_: Any) -> subprocess.CompletedProcess[str]:
+        """Capture the act subprocess command without executing it."""
         captured_command.extend(command)
         return subprocess.CompletedProcess(command, 0, "stdout", "stderr")
 
diff --git a/tests/test_helpers.py b/tests/test_helpers.py
index 976a7fe..b549b42 100644
--- a/tests/test_helpers.py
+++ b/tests/test_helpers.py
@@ -456,6 +456,9 @@ def test_parent_makefile_test_target_uses_requisite_pytest_command() -> None:
     assert "$(UV) ruff check tests/" in makefile, (
         "expected parent Makefile lint target to run Ruff checks"
     )
+    assert "$(UV) --with interrogate interrogate --fail-under 100 tests/" in makefile, (
+        "expected parent Makefile lint target to enforce docstring coverage"
+    )
     assert "typecheck: ## Run template test type checks" in makefile, (
         "expected parent Makefile to expose a documented typecheck target"
     )
diff --git a/tests/test_interrogate_lint.py b/tests/test_interrogate_lint.py
new file mode 100644
index 0000000..a6aa930
--- /dev/null
+++ b/tests/test_interrogate_lint.py
@@ -0,0 +1,97 @@
+"""Validate rendered docstring coverage lint behaviour.
+
+These integration tests render a project from the Copier template and exercise
+its public ``make lint`` target instead of inspecting only generated text.  They
+prove that a clean render passes the full Python lint tier, then mutate the
+rendered package to introduce a Ruff-clean missing private docstring and verify
+that Interrogate fails the target.
+
+The module protects the template contract that generated projects enforce 100%
+docstring coverage through their normal lint workflow.
+"""
+
+from __future__ import annotations
+
+import re
+import shutil
+import subprocess
+from pathlib import Path
+
+from pytest_copier.plugin import CopierFixture
+
+from tests.helpers.rendering import render_project
+
+
+def test_generated_make_lint_enforces_interrogate_docstrings(
+    copier: CopierFixture, tmp_path: Path
+) -> None:
+    """Validate rendered ``make lint`` fails on missing private docstrings.
+
+    Parameters
+    ----------
+    copier : CopierFixture
+        Fixture used to render the template into a temporary project.
+    tmp_path : Path
+        Temporary directory used as the generated project root.
+
+    Returns
+    -------
+    None
+        The test passes when a complete generated project passes ``make lint``
+        and a private helper without a docstring fails at the Interrogate gate.
+    """
+    package_name = "lint_docstrings_pkg"
+    project = render_project(
+        tmp_path / "lint-docstrings",
+        copier,
+        project_name="LintDocstrings",
+        package_name=package_name,
+        use_rust=False,
+    )
+    make = shutil.which("make")
+    assert make is not None, "expected make to be available for generated tests"
+
+    passing_result = subprocess.run(
+        [make, "lint"],
+        cwd=project.path,
+        check=False,
+        capture_output=True,
+        text=True,
+    )
+    assert passing_result.returncode == 0, (
+        f"expected generated make lint to pass with complete docstrings:\n"
+        f"{passing_result.stdout}\n{passing_result.stderr}"
+    )
+
+    pure_module = project / package_name / "pure.py"
+    undocumented_helper = (
+        '\n\ndef _missing_interrogate_docstring() -> str:\n    return "undocumented"\n'
+    )
+    pure_module.write_text(
+        pure_module.read_text(encoding="utf-8") + undocumented_helper,
+        encoding="utf-8",
+    )
+
+    failing_result = subprocess.run(
+        [make, "lint"],
+        cwd=project.path,
+        check=False,
+        capture_output=True,
+        text=True,
+    )
+    output = f"{failing_result.stdout}\n{failing_result.stderr}"
+    assert failing_result.returncode != 0, (
+        "expected generated make lint to fail when Interrogate finds a missing "
+        f"private docstring:\n{output}"
+    )
+    assert "RESULT: FAILED" in output, (
+        "expected generated make lint to run the Interrogate docstring gate"
+    )
+    actual_match = re.search(r"actual:\s+([0-9]+(?:\.[0-9]+)?)%", output)
+    assert actual_match is not None, (
+        f"expected Interrogate output to report actual docstring coverage:\n{output}"
+    )
+    actual_coverage = float(actual_match.group(1))
+    assert actual_coverage < 100.0, (
+        "expected Interrogate output to report reduced docstring coverage"
+    )
diff --git a/tests/utilities.py b/tests/utilities.py
index 29a7fc7..bc5b9ea 100644
--- a/tests/utilities.py
+++ b/tests/utilities.py
@@ -39,6 +39,7 @@
 def _resolved_socket_from_docker_host(
     docker_host: str, allowed_dirs: tuple[Path, ...]
 ) -> Path | None:
+    """Return a trusted Unix socket path parsed from ``DOCKER_HOST``."""
     parsed = urlparse(docker_host)
     if parsed.scheme != "unix" or parsed.netloc or not parsed.path:
         return None
@@ -54,6 +55,7 @@ def _resolved_socket_from_docker_host(
 
 
 def _user_podman_socket() -> Path | None:
+    """Return the current user's Podman socket when it exists under runtime dir."""
     socket_path = Path(f"/run/user/{os.getuid()}/podman/podman.sock")
     if not socket_path.exists():
         return None