diff --git a/etl-service/src/test/java/com/xtrmetl/etl/documentation/LocalComposeLoopbackBindingTest.java b/etl-service/src/test/java/com/xtrmetl/etl/documentation/LocalComposeLoopbackBindingTest.java
new file mode 100644
index 00000000..6d082b55
--- /dev/null
+++ b/etl-service/src/test/java/com/xtrmetl/etl/documentation/LocalComposeLoopbackBindingTest.java
@@ -0,0 +1,75 @@
+package com.xtrmetl.etl.documentation;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Verifies that the bundled local Docker Compose profile does not publish ports on all host
+ * interfaces by default.
+ *
+ * <p>Compose service-to-service traffic uses the internal network and service names. Published
+ * host ports are therefore a developer-access boundary and must be explicitly loopback-bound in
+ * the default local profile. This test does not claim that loopback binding is a production
+ * authentication or transport-security control.</p>
+ */
+class LocalComposeLoopbackBindingTest {
+
+    private static final Path PROJECT_ROOT = findProjectRoot();
+
+    @Test
+    void everyPublishedPortIsExplicitlyLoopbackBound() throws IOException {
+        List<String> publishedPorts = Files.readAllLines(
+                        PROJECT_ROOT.resolve("docker-compose.yml"),
+                        StandardCharsets.UTF_8
+                ).stream()
+                .map(String::trim)
+                .filter(LocalComposeLoopbackBindingTest::isPublishedPortMapping)
+                .toList();
+
+        assertFalse(
+                publishedPorts.isEmpty(),
+                "The local Compose contract must exercise at least one published host port"
+        );
+
+        List<String> nonLoopbackBindings = publishedPorts.stream()
+                .filter(mapping -> !mapping.startsWith("- \"127.0.0.1:"))
+                .toList();
+
+        assertTrue(
+                nonLoopbackBindings.isEmpty(),
+                () -> "Default local Compose ports must bind to 127.0.0.1; unsafe mappings: "
+                        + nonLoopbackBindings
+        );
+    }
+
+    private static boolean isPublishedPortMapping(String line) {
+        return line.matches("- \\\"(?:127\\.0\\.0\\.1:)?[0-9]+:[0-9]+\\\"");
+    }
+
+    private static Path findProjectRoot() {
+        Path current = Paths.get(System.getProperty("user.dir")).toAbsolutePath();
+        Path lastPomParent = null;
+        while (current != null) {
+            if (Files.exists(current.resolve(".git"))) {
+                return current;
+            }
+            if (Files.exists(current.resolve("pom.xml"))) {
+                lastPomParent = current;
+            }
+            current = current.getParent();
+        }
+        if (lastPomParent != null) {
+            return lastPomParent;
+        }
+        throw new IllegalStateException("Could not find project root (no .git or pom.xml found)");
+    }
+}