diff --git a/tools/mdx-lint/mdx-lint.mjs b/tools/mdx-lint/mdx-lint.mjs
index 659a548..0505904 100644
--- a/tools/mdx-lint/mdx-lint.mjs
+++ b/tools/mdx-lint/mdx-lint.mjs
@@ -175,8 +175,12 @@ function validateTree(tree) {
       case "html":
         fail(node, "contains raw HTML");
         break;
-      case "link":
+      // Embedded images make the registry's MDX renderer emit a <link rel=preload>, which its HTML validator rejects.
       case "image":
+      case "imageReference":
+        fail(node, "contains an embedded image; connector docs must not embed images");
+        break;
+      case "link":
       case "definition":
         validateUrlNode(node);
         break;
diff --git a/tools/mdx-lint/testdata/shared-mdx-validation.json b/tools/mdx-lint/testdata/shared-mdx-validation.json
index 1651673..fb8626d 100644
--- a/tools/mdx-lint/testdata/shared-mdx-validation.json
+++ b/tools/mdx-lint/testdata/shared-mdx-validation.json
@@ -96,5 +96,17 @@
     "valid": false,
     "errorContains": "dangerous URL scheme",
     "content": "[link](java&#x73;cript:alert(1))\n"
+  },
+  {
+    "name": "reject markdown embedded image",
+    "valid": false,
+    "errorContains": "must not embed images",
+    "content": "![diagram](./images/diagram.png)\n"
+  },
+  {
+    "name": "reject markdown image reference",
+    "valid": false,
+    "errorContains": "must not embed images",
+    "content": "![diagram][ref]\n\n[ref]: ./images/diagram.png\n"
   }
 ]