A NextCloud app for metadata validation?
An app for NextCloud that can validate a JSON/YAML/TOML files containing metadata according to a selectable schema could be interesting.
The UI could be similar to the checksum app.
Implementations for JSON schema validators in PHP: https://json-schema.org/implementations.html#validator-php
Implementations for JSON schema validators in JavaScript: https://json-schema.org/implementations.html#validator-javascript