SQL Server 2016 and upwards has a useful feature where JSON data can be validated through SQL Code.
There are two ways of doing this:
Inline in a SQL Function/Procedure
IF (ISJSON(@json) = 1)
'Is valid JSON'
As part of a check constraint on a table
CREATE TABLE Person ( ID INT IDENTITY PRIMARY KEY, json NVARCHAR(MAX) CONSTRAINT [Content should be formatted as JSON] CHECK ( ISJSON(json )>0 ) )