diff --git a/api-playground/openapi-setup.mdx b/api-playground/openapi-setup.mdx
index fb985ee6e..55364cef9 100644
--- a/api-playground/openapi-setup.mdx
+++ b/api-playground/openapi-setup.mdx
@@ -128,6 +128,29 @@ If different endpoints within your API require different methods of authenticati
 
 For more information on defining and applying authentication, see [Authentication](https://swagger.io/docs/specification/authentication/) in the OpenAPI documentation.
 
+#### Set default values for security schemes
+
+Use the `x-default` extension on a security scheme to pre-fill the authentication field in the API playground. This is useful for providing placeholder values or test credentials that help users get started quickly.
+
+```json {6}
+{
+  "components": {
+    "securitySchemes": {
+      "apiKey": {
+        "type": "apiKey",
+        "in": "header",
+        "name": "X-API-Key",
+        "x-default": "your-api-key-here"
+      }
+    }
+  }
+}
+```
+
+The `x-default` extension is supported on `apiKey` and `http` bearer security scheme types. The value appears as the default input in the playground's authentication fields.
+
+You can also use `x-default` on any schema property in your OpenAPI specification to set a default value in the API playground without affecting the `default` field in the schema definition.
+
 ## Customize your endpoint pages
 
 Customize your endpoint pages by adding the `x-mint` extension to your OpenAPI specification. The `x-mint` extension gives you additional control over how your API documentation generates and displays.