Validation

link - docs.microsoft.com/en-us/office/dev/add-ins/testing/troubleshoot-manifest
link - docs.microsoft.com/en-us/office/dev/add-ins/testing/runtime-logging

Yeoman Generator

Your add-in project must have been created by using Yeoman generator for Office Add-ins version 1.1.17 or later.

npm run validate 

office-addin-manifest

This package provides the ability to parse, display, modify, and validate the manifest file for Office Add-ins.
This is being constantly updated.

office-addin-validator

This was first released in 2016 and was last updated in 2017.

office-addin-dev-settings

This can help you identify issues with your manifest that are not detected by XSD schema validation, such as a mismatch between resource IDs.
This is being constantly updated.