The GraphQLView and its async version allow overriding the template file. However, the loading of the template is incorrect, resulting in JSON.parse("") // empty string , because the variable is already replaced.

Additional Context

In the view we see the following code:

        try:
            template = Template(render_to_string("graphql/graphiql.html"))
        except TemplateDoesNotExist:
            template = Template(self.graphql_ide_html)

The loading in the try section, erronously calls render_to_string and sticks the result into a Template class. However, render_to_string already renders the entire template, replacing its variables.