Protect leading zeros and long IDs
The tools preserve CSV cell values as strings by default. IDs such as 00123 and 12345678901234567 must not be silently converted to JavaScript numbers. JSON input numbers are read without rounding their original numeric text.
Turning off Keep values as text allows exact, safe scalar conversion for CSV to JSON: booleans, null and safely representable canonical numbers. Leading-zero IDs, oversized integers and imprecise decimals remain strings. Dates are not inferred.
CSV cannot declare column types. Preserving file text does not guarantee that Excel will keep those values when you open it. Use Excel Data > From Text/CSV and set ID columns to Text. Once another application has removed digits or zeros, this tool cannot reconstruct the original values.
JSON to CSV accepts arrays of flat objects. Headers are the union of object keys. Null and absent fields become empty CSV cells with an explicit warning. Nested objects and arrays are rejected. Duplicate object keys and ambiguous CSV headers block object-based JSON output.