Having a configuration file schema would clearly make tox easier to use.

• Users would know right away if they had a typo, like the famous skipdist vs skipsdist.
• With a published schema, code editors can verify it on the fly and implement auto-complete

While this ticked may remind us about #999 I do not think that changing configuration format should be required in order to implement schema validation.

Making a new configuration format would be out of the scope but I am wondering if we could learn from http://schemastore.org/json/ which covers both json and yaml. One such validator for vscode can be seen at https://marketplace.visualstudio.com/items?itemName=redhat.vscode-yaml -- I used it to validate some other file formats.

Maybe we could extend the existing validators to also use these schema format for validating ini files.