When to reformat JSON and when to validate it, and why the two tools answer different questions.
A formatter changes whitespace and optionally key order; a validator answers whether the document follows the JSON grammar. They are complementary, not interchangeable.
Which should you reach for?
Use the validator when you need a yes/no answer and an error position.
Use the formatter when you need readable output without changing values.
Use both when a document fails and you need to locate and fix the problem.