diff --git a/.editorconfig b/.editorconfig
index 58de178..d3c791b 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -5,3 +5,8 @@ root = true
 end_of_line = lf
 charset = utf-8
 insert_final_newline = true
+
+[*.sh]
+indent_style = space
+indent_size = 2
+switch_case_indent = true
diff --git a/.gitea/workflows/validate-workflows.yml b/.gitea/workflows/validate-workflows.yml
index e31f372..68defb6 100644
--- a/.gitea/workflows/validate-workflows.yml
+++ b/.gitea/workflows/validate-workflows.yml
@@ -26,3 +26,9 @@ jobs:
 
       - name: Check the coverage of the tools
         run: .venv/bin/python -m coverage report
+
+      - name: Lint the shell scripts of the actions
+        env:
+          SHELLCHECK: .venv/bin/shellcheck
+          SHFMT: .venv/bin/shfmt
+        run: bash tools/lint-action-scripts.sh actions
diff --git a/tests/requirements.txt b/tests/requirements.txt
index e18e2b4..cfb4328 100644
--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -1,3 +1,5 @@
 pytest>=8,<10
 PyYAML>=6,<7
 coverage>=7,<8
+shellcheck-py==0.10.0.1
+shfmt-py==3.11.0.2
diff --git a/tests/test_lint_action_scripts.py b/tests/test_lint_action_scripts.py
new file mode 100644
index 0000000..a13f63c
--- /dev/null
+++ b/tests/test_lint_action_scripts.py
@@ -0,0 +1,86 @@
+"""Offline tests for tools/lint-action-scripts.sh (MIL-012 task 6).
+
+The script runs shellcheck and shfmt on a folder; the tests give it a clean
+script, a script with a shellcheck problem and a badly formatted one, so a
+seeded error is shown to fail the run.
+"""
+
+import os
+import shutil
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+import yaml
+
+from workflow_source import REPO_ROOT
+
+SCRIPT = REPO_ROOT / "tools" / "lint-action-scripts.sh"
+WORKFLOW = REPO_ROOT / ".gitea" / "workflows" / "validate-workflows.yml"
+BASH = shutil.which("bash")
+# the tools are in the virtual environment of the interpreter that runs the tests
+SEARCH_PATH = os.pathsep.join([str(Path(sys.executable).parent), os.environ.get("PATH", "")])
+SHELLCHECK = shutil.which("shellcheck", path=SEARCH_PATH)
+SHFMT = shutil.which("shfmt", path=SEARCH_PATH)
+HAVE_TOOLS = BASH and SHELLCHECK and SHFMT
+
+CLEAN = '#!/usr/bin/env bash\nmain() {\n  echo "$1"\n}\n\nmain "$@"\n'
+SHELLCHECK_PROBLEM = '#!/usr/bin/env bash\nmain() {\n  echo $1\n}\n\nmain "$@"\n'
+BADLY_FORMATTED = '#!/usr/bin/env bash\nmain() {\n        echo "$1"\n}\n\nmain "$@"\n'
+
+
+def lint(folder: Path) -> subprocess.CompletedProcess:
+    # shfmt reads .editorconfig from the folder upwards; a temporary folder is
+    # outside this repository, so it gets a copy of the repository's file
+    if folder != REPO_ROOT / "actions":
+        shutil.copy(REPO_ROOT / ".editorconfig", folder / ".editorconfig")
+    env = {**os.environ, "SHELLCHECK": str(SHELLCHECK), "SHFMT": str(SHFMT)}
+    return subprocess.run(
+        [BASH, str(SCRIPT), str(folder)],
+        capture_output=True,
+        text=True,
+        check=False,
+        cwd=REPO_ROOT,
+        env=env,
+    )
+
+
+@pytest.mark.skipif(not HAVE_TOOLS, reason="bash, shellcheck and shfmt are needed")
+class TestLint:
+    def test_a_clean_script_passes(self, tmp_path):
+        (tmp_path / "ok.sh").write_bytes(CLEAN.encode())  # LF on every platform
+        result = lint(tmp_path)
+        assert result.returncode == 0, result.stdout + result.stderr
+        assert "clean" in result.stdout
+
+    def test_a_shellcheck_problem_fails(self, tmp_path):
+        (tmp_path / "bad.sh").write_bytes(SHELLCHECK_PROBLEM.encode())  # LF on every platform
+        result = lint(tmp_path)
+        assert result.returncode == 1
+        assert "::error::[lint] shellcheck" in result.stdout
+
+    def test_a_badly_formatted_script_fails(self, tmp_path):
+        (tmp_path / "ugly.sh").write_bytes(BADLY_FORMATTED.encode())  # LF on every platform
+        result = lint(tmp_path)
+        assert result.returncode == 1
+        assert "::error::[lint] shfmt" in result.stdout
+
+    def test_no_scripts_is_not_a_failure(self, tmp_path):
+        result = lint(tmp_path)
+        assert result.returncode == 0
+        assert "nothing was checked" in result.stdout
+
+    def test_the_scripts_of_the_actions_are_clean(self):
+        result = lint(REPO_ROOT / "actions")
+        assert result.returncode == 0, result.stdout + result.stderr
+
+
+class TestWorkflow:
+    def test_validate_workflows_runs_the_lint_with_pinned_tools(self):
+        document = yaml.safe_load(WORKFLOW.read_text(encoding="utf-8"))
+        commands = [step.get("run", "") for step in document["jobs"]["validate"]["steps"]]
+        assert any("tools/lint-action-scripts.sh" in command for command in commands)
+        requirements = (REPO_ROOT / "tests" / "requirements.txt").read_text(encoding="utf-8")
+        assert "shellcheck-py==" in requirements
+        assert "shfmt-py==" in requirements
diff --git a/tools/lint-action-scripts.sh b/tools/lint-action-scripts.sh
new file mode 100644
index 0000000..1e680d5
--- /dev/null
+++ b/tools/lint-action-scripts.sh
@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Lint the shell scripts of the composite actions (MIL-012 task 6): shellcheck,
+# and shfmt in the format .editorconfig sets (two spaces, indented case labels).
+# validate-workflows.yml runs it on every pull request and push to main.
+#
+# Usage:   lint-action-scripts.sh [<directory>]     (default: actions)
+# Env:     SHELLCHECK, SHFMT  the commands to run (default: from the PATH)
+# Exit:    0 every script is clean (or there is none); 1 at least one finding or
+#          a missing tool
+# Needs:   bash, find, shellcheck, shfmt
+
+SHELLCHECK="${SHELLCHECK:-shellcheck}"
+SHFMT="${SHFMT:-shfmt}"
+
+main() {
+  set -u
+  local dir="${1:-actions}" failed=0 tool
+  for tool in "$SHELLCHECK" "$SHFMT"; do
+    command -v "$tool" >/dev/null 2>&1 || {
+      echo "::error::[environment] $tool is not installed."
+      exit 1
+    }
+  done
+  local files=()
+  while IFS= read -r file; do
+    files+=("$file")
+  done < <(find "$dir" -name '*.sh' -type f | sort)
+  if [ "${#files[@]}" -eq 0 ]; then
+    echo "::notice::No shell scripts under '$dir'; nothing was checked."
+    exit 0
+  fi
+  "$SHELLCHECK" "${files[@]}" || {
+    echo "::error::[lint] shellcheck found problems."
+    failed=1
+  }
+  "$SHFMT" -d "${files[@]}" || {
+    echo "::error::[lint] shfmt would change a script; run shfmt -w."
+    failed=1
+  }
+  [ "$failed" -eq 0 ] && echo "Checked ${#files[@]} script(s): clean."
+  exit "$failed"
+}
+
+main "$@"