Mandatory human rights due diligence (mHRDD) laws are currently being proposed and/or implemented in countries around the world. Increasingly, these laws place obligations on corporations to establish or participate in corporate grievance mechanisms (CGMs). CGMs have the potential to ensure that rightsholders are empowered to hold corporations accountable for their human rights performance. But our limited knowledge of how CGMs operate indicates that many are not producing results that are valuable for workers and communities. CGM provisions in mHRDD laws in Germany and Norway, and draft laws produced in the European Union and Brazil are rudimentary and unlikely to produce better-performing CGMs. Analysis of Norwegian mHRDD corporate reporting identifies that many corporations fail to understand the basic elements of an effective CGM. The article therefore argues that requirements for CGMs in mHRDD laws will only be a progressive move if such laws also demand disclosure of information that empowers national authorities, as well as civil society actors and researchers, to scrutinize CGMs to ensure they are effective. Disclosure requirements must speak to three issues: (1) how accessible CGMs are, (2) the way complaints are handled, and (3) the remedies provided to rightsholders. If, as a result of scrutiny of this data, mHRDD laws can produce well-functioning CGMs, this could lead to rightsholder concerns becoming more central to due diligence processes, potentially addressing cosmetic compliance with due diligence obligations.