Appcache has been marked as deprecated in browsers and will be removed soon, also from the future HTML spec.
This service will shut down on January, 1st 2017. Code is available on GitHub, but won't be maintained any longer.
The most complete method is to upload the manifest file to your server and validate it by URI. This will also check the availability of all resources listed in your manifest – if even one of them fails to download properly, the entire process of caching your offline web application will fail.
To learn more about offline web applications and cache manifest files, check the following resources:
Try out the interactive Cache Manifest Validator API documentation.