CSV is strong for tables; JSON for structure
CSV works well when every record has the same columns and is easy to open in spreadsheets. JSON is better for hierarchical data such as API responses and configuration objects.
Check nesting before JSON → CSV
Simple keys such as name, email and age map cleanly to columns. Nested addresses or tag arrays need a rule for flattening, and different converters may handle them differently.
Watch strings that look like numbers
Postal codes, product IDs and phone numbers can lose leading zeros when a spreadsheet treats them as numbers. Date-like strings may also be converted automatically.
Verify meaning, not only row count
The number of records can match while nested values have been flattened or reformatted. Compare a few representative records with the original after conversion.