Grey literature can be difficult to find and to evaluate. It does not usually have the same quality checking as peer-reviewed material, so careful evaluation of the source, the author, and the contents is recommended.
One available evaluation tool is the AACODS checklist, which provides guidance when dealing with diverse formats of grey literature. The checklist can be used for any discipline area and prioritises expert opinion and expertise over source format.
If you are conducting a review or looking for evidence to support your clinical practice, select the appropriate critical appraisal tool to evaluate the information.
For example, if you have found a relevant unpublished trial through searching clinical trial registers, you should appraise this the same way you would a published trial.