diff --git a/README.md b/README.md
index 1f9491b..56b5210 100644
--- a/README.md
+++ b/README.md
@@ -86,6 +86,7 @@ More
 ------------
 
 * [Custom HTTP headers](Resources/doc/custom-http-headers.md)
+* [Custom GraphiQL parameters](Resources/doc/custom-parameters.md)
 * [Define JavaScript libraries' versions](Resources/doc/libraries-versions.md)
 * [Define a custom GraphQL endpoint](Resources/doc/graphql-endpoint.md)
 
diff --git a/Resources/doc/custom-parameters.md b/Resources/doc/custom-parameters.md
new file mode 100644
index 0000000..0e1a068
--- /dev/null
+++ b/Resources/doc/custom-parameters.md
@@ -0,0 +1,29 @@
+Custom GraphiQL parameters
+==========================
+
+By default, only the `fetcher` parameter is passed to GraphiQL's React component.
+To add more:
+
+1. Override the default GraphiQL template:
+
+```yaml
+# config/packages/graphiql.yaml or app/config/config.yml for Symfony without Flex
+overblog_graphiql:
+    template: "GraphiQL/index.html.twig"
+```
+
+2. Create a new template:
+
+```twig
+{# templates/GraphiQL/index.html.twig #}
+{% extends '@OverblogGraphiQL/GraphiQL/index.html.twig' %}
+
+{% block graphiql_params %}
+{{ parent() }},
+defaultQuery: `query SomeQuery($param: String) {
+  items(param: $param) {
+    someField
+  }
+}`
+{% endblock graphiql_params %}
+```
diff --git a/Resources/views/GraphiQL/index.html.twig b/Resources/views/GraphiQL/index.html.twig
index 0cf897d..ada9714 100644
--- a/Resources/views/GraphiQL/index.html.twig
+++ b/Resources/views/GraphiQL/index.html.twig
@@ -58,7 +58,9 @@
 
       ReactDOM.render(
         React.createElement(GraphiQL, {
+          {% block graphiql_params %}
           fetcher: graphQLFetcher
+          {% endblock graphiql_params %}
         }),
         document.body
       )