You could make a view of your nodes then use

[Views Datasource][1]

> Views Datasource is a set of plugins for Drupal Views for rendering
> content in a number of shareable, reusable formats based on XML, JSON
> and XHTML.

For how to use, see the accepted answer to this [Views JSON output](https://drupal.stackexchange.com/questions/60499/views-json-output)

  [1]: https://www.drupal.org/project/views_datasource