Use the externally_connectable schema from manifest_types.json to generate its

chrome/common/extensions/docs/templates/articles/manifest/externally_connectable.html

+<h1>externally_connectable</h1>
+
+<p>
+The <code>externally_connectable</code> manifest property declares which extensions, apps, and web pages can connect to your extension via <a href="../runtime.html#method-connect">runtime.connect</a> and <a href="../runtime.html#method-sendMessage">runtime.sendMessage</a>.
+</p>
+
+<p>
+For a tutorial on message passing see <a href="../messaging.html#external">cross-extension and app messaging</a> and <a href="../messaging.html#external-webpage">sending messages from web pages</a>.
+</p>
+
+<h2 id="manifest">Sample manifest.json</h2>
+<pre>
+{
+  "name": "My externally connectable {{platform}}",
+  "externally_connectable": {
+    // Extension and app IDs:
+    "ids": [
+      "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+      "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
+      ...
+    ],
+    // Alternatively, for all extensions and apps:
+    "ids": ["*"],
+    // Match patterns for <em>web pages</em>, not content scripts:
+    "matches": [
+      "https://*.google.com",
+      "*://*.chromium.org",
+      ...
+    ]
+  },
+  ...
+}
+</pre>
+
+<h2 id="reference">Reference</h2>
+<p class="api_reference">
+{{+partials.type @:apis.manifestTypes.byName.ExternallyConnectable}}
+</p>