diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..06cdc9f
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,275 @@
+"""Tests for CLI commands."""
+import json
+import tempfile
+from pathlib import Path
+
+from click.testing import CliRunner
+
+from i18n_key_sync.cli import main
+
+
+class TestCLIExtract:
+    """Tests for extract command."""
+
+    def test_extract_from_python_file(self, sample_python_code):
+        """Test extracting keys from Python file."""
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write(sample_python_code)
+            f.flush()
+            f_path = f.name
+
+        runner = CliRunner()
+        result = runner.invoke(main, ["extract", f_path])
+
+        assert result.exit_code == 0
+        assert "hello" in result.output or "hello" in result.output.lower()
+        assert "goodbye" in result.output or "goodbye" in result.output.lower()
+
+        Path(f_path).unlink()
+
+    def test_extract_json_output(self, sample_python_code):
+        """Test extract with JSON output format."""
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write('_("test_key")')
+            f.flush()
+            f_path = f.name
+
+        runner = CliRunner()
+        result = runner.invoke(main, ["--output-format", "json", "extract", f_path])
+
+        assert result.exit_code == 0
+        data = json.loads(result.output)
+        assert "test_key" in data
+
+        Path(f_path).unlink()
+
+    def test_extract_with_patterns(self, sample_python_code):
+        """Test extract with custom patterns."""
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write('t("custom_key")')
+            f.flush()
+            f_path = f.name
+
+        runner = CliRunner()
+        result = runner.invoke(main, ["extract", f_path, "--patterns", "t"])
+
+        assert result.exit_code == 0
+        assert "custom_key" in result.output
+
+        Path(f_path).unlink()
+
+
+class TestCLIValidate:
+    """Tests for validate command."""
+
+    def test_validate_valid_keys(self, temp_project_dir, temp_locale_dir):
+        """Test validation with all keys present."""
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "validate",
+            str(temp_project_dir / "src"),
+        ])
+
+        assert result.exit_code == 0
+        assert "valid" in result.output.lower() or "matching" in result.output.lower()
+
+    def test_validate_missing_keys(self, tmp_path, temp_locale_dir):
+        """Test validation with missing keys."""
+        src_dir = tmp_path / "src"
+        src_dir.mkdir()
+
+        code_file = src_dir / "main.py"
+        code_file.write_text('_("nonexistent_key")')
+
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "validate",
+            str(src_dir),
+        ])
+
+        assert result.exit_code in [0, 1]
+        assert "missing" in result.output.lower() or "nonexistent_key" in result.output
+
+    def test_validate_strict_mode(self, tmp_path, temp_locale_dir):
+        """Test validation in strict mode."""
+        src_dir = tmp_path / "src"
+        src_dir.mkdir()
+
+        code_file = src_dir / "main.py"
+        code_file.write_text('_("missing_key")\n_("unused_in_locale")')
+
+        locale_file = temp_locale_dir / "en.json"
+        locale_data = json.loads(locale_file.read_text())
+        locale_data["unused_in_locale"] = "Unused"
+        locale_file.write_text(json.dumps(locale_data, indent=2))
+
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "validate",
+            str(src_dir),
+            "--strict",
+        ])
+
+        assert result.exit_code == 3
+
+    def test_validate_json_output(self, temp_project_dir, temp_locale_dir):
+        """Test validate with JSON output."""
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--output-format", "json",
+            "--locale-dir", str(temp_locale_dir),
+            "validate",
+            str(temp_project_dir / "src"),
+        ])
+
+        assert result.exit_code == 0
+        data = json.loads(result.output)
+        assert "missing_keys" in data
+        assert "unused_keys" in data
+        assert "matching_keys" in data
+
+
+class TestCLISync:
+    """Tests for sync command."""
+
+    def test_sync_dry_run(self, tmp_path, temp_locale_dir):
+        """Test sync in dry run mode."""
+        src_dir = tmp_path / "src"
+        src_dir.mkdir()
+
+        code_file = src_dir / "main.py"
+        code_file.write_text('_("new_key")')
+
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "sync",
+            str(src_dir),
+            "--dry-run",
+        ])
+
+        assert result.exit_code == 0
+        assert "DRY RUN" in result.output or "dry" in result.output.lower()
+
+        locale_file = temp_locale_dir / "en.json"
+        locale_data = json.loads(locale_file.read_text())
+        assert "new_key" not in locale_data
+
+    def test_sync_actual(self, tmp_path, temp_locale_dir):
+        """Test actual sync modifies files."""
+        src_dir = tmp_path / "src"
+        src_dir.mkdir()
+
+        code_file = src_dir / "main.py"
+        code_file.write_text('_("new_sync_key")')
+
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "sync",
+            str(src_dir),
+        ])
+
+        assert result.exit_code == 0
+
+        locale_file = temp_locale_dir / "en.json"
+        locale_data = json.loads(locale_file.read_text())
+        assert "new_sync_key" in locale_data
+
+    def test_sync_custom_placeholder(self, tmp_path, temp_locale_dir):
+        """Test sync with custom placeholder value."""
+        src_dir = tmp_path / "src"
+        src_dir.mkdir()
+
+        code_file = src_dir / "main.py"
+        code_file.write_text('_("placeholder_key")')
+
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "sync",
+            str(src_dir),
+            "--value", "TRANSLATE_ME",
+        ])
+
+        assert result.exit_code == 0
+
+        locale_file = temp_locale_dir / "en.json"
+        locale_data = json.loads(locale_file.read_text())
+        assert locale_data["placeholder_key"] == "TRANSLATE_ME"
+
+
+class TestCLIReport:
+    """Tests for report command."""
+
+    def test_report_generates_output(self, temp_project_dir, temp_locale_dir):
+        """Test report command generates output."""
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "report",
+            str(temp_project_dir / "src"),
+        ])
+
+        assert result.exit_code == 0
+        assert len(result.output) > 0
+
+    def test_report_json_format(self, temp_project_dir, temp_locale_dir):
+        """Test report with JSON format."""
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "report",
+            str(temp_project_dir / "src"),
+            "--format", "json",
+        ])
+
+        assert result.exit_code == 0
+        data = json.loads(result.output)
+        assert "summary" in data
+
+    def test_report_markdown_format(self, temp_project_dir, temp_locale_dir):
+        """Test report with markdown format."""
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "report",
+            str(temp_project_dir / "src"),
+            "--format", "markdown",
+        ])
+
+        assert result.exit_code == 0
+        assert "# i18n Key Report" in result.output
+
+    def test_report_to_file(self, temp_project_dir, temp_locale_dir, tmp_path):
+        """Test report output to file."""
+        output_file = tmp_path / "report.md"
+
+        runner = CliRunner()
+        result = runner.invoke(main, [
+            "--locale-dir", str(temp_locale_dir),
+            "report",
+            str(temp_project_dir / "src"),
+            "--output", str(output_file),
+            "--format", "markdown",
+        ])
+
+        assert result.exit_code == 0
+        assert output_file.exists()
+        content = output_file.read_text()
+        assert "# i18n Key Report" in content
+
+
+class TestCLIVersion:
+    """Tests for version flag."""
+
+    def test_version_flag(self):
+        """Test --version flag displays version."""
+        runner = CliRunner()
+        result = runner.invoke(main, ["--version"])
+
+        assert result.exit_code == 0
+        assert "i18n-key-sync" in result.output