Hi all!

This is an announcement for a breaking change to the output of the WikibaseQualityConstraints constraint checking API, to go live on 18 December 2017. It potentially affects clients that use the *wbcheckconstraints* API action. (We are not aware of any such clients apart from the *checkConstraints* gadget, which is not affected.)

Currently, the description of a constraint in the API response includes the detail and detailHTML fields, which contain the constraint parameters. The gadget has never used these fields, since the error messages for some time now contain all the information needed to understand the constraint violation (that is, the constraint parameters are part of the message where necessary). Additionally, since the move from the {{Constraint https://www.wikidata.org/wiki/Template:Constraint}} templates to constraint statements on properties (using property constraint (P2302) https://www.wikidata.org/wiki/Property:P2302), parsing constraint parameters is no longer the complex task it once was, and consumers interested in the constraint parameters can inspect the constraint statements using the standard Wikibase APIs or the Wikidata Query Service.

Since these two fields can account for up to 40% of the *wbcheckconstraints* API response size, and we want to start caching those responses soon, *we will remove the detail and detailHTML fields on 18 December 2017.* This is already in effect on the Wikidata constraints test system https://wikidata-constraints.wmflabs.org/; you can test your tools or other code there.

Please let us know if you have any comments or objections. -- Lucas

Relevant tickets:

- phab:T180614 https://phabricator.wikimedia.org/T180614

Relevant patches:

- gerrit:391864 https://gerrit.wikimedia.org/r/391864