Can SQL Server 2016 validate JSON on insert? Currently SQL Server 2016 CTP 3 and later releases support NVARCHAR(max) fields with JSON content. However since the type NVARCHAR(max) is totally free-form, there is no constraint on these fields. 

Can I declare a constraint that prevents insertion of a non-null value that is not valid JSON?
Add this constraint:

ALTER TABLE [dbo].[Resource] 
 ADD CONSTRAINT [RESOURCE_ExtJSON_VALID] 
   CHECK ( ISJSON( ExtJSON )&gt; 0 )