You can verify the REST Service content by using the special validation service before saving.

To do that, simply click on the toolbar;

Or, go to Run → Validate from the top menu. In case of no errors in the service, there will be a message in the Output tab:

Otherwise, there will be an error message displayed in the Output tab:

You can click the error message in the Output panel to go to the line containing the error in the REST Service file. In case the file has been closed, eXo IDE will automatically open it. Make sure that you do not delete or rename this file after the error message has been displayed in the Outline panel.