There are at least two third-party implementations of constraint checks – [HarvestTemplates](https://tools.wmflabs.org/pltools/harvesttemplates/) ([code](https://github.com/Pascalco/harvesttemplates/blob/86b38d29262b1705c96439247ae536d6e35ffc42/main.js#L400-L553)) and [OpenRefine](http://openrefine.org/) ([code](https://github.com/OpenRefine/OpenRefine/tree/master/extensions/wikidata/src/org/openrefine/wikidata/qa/scrutinizers)) – which check constraints on some data before adding it to Wikidata. It would be nice if we supported this in WikibaseQualityConstraints, so that third parties don’t have to re-implement everything.
Technically, this means adding support for passing JSON snippets (snaks, full statements, or full entities?) instead of entity or statement IDs into `wbcheckentities`. (I think that makes more sense than a separate API module.)
@Pintoch perhaps we can work on this during #wikimedia-hackathon-2018 – I’ll add support to WikibaseQualityConstraints and you try to use it in OpenRefine? :)