Keep leading zeros and long IDs when converting CSV to JSON

1. Treat an identifier as text

A customer ID is a label, even when it contains only digits. Keep 0012 and long identifiers as text in the source spreadsheet before entering or importing them. Applying a display format after digits have already been removed or rounded does not recover the original value. Keep a backup and compare with the authoritative source.

2. Inspect the CSV before converting

Export a UTF-8 CSV and open it in a text editor. Confirm that leading zeros and every digit are present. Our converter cannot reconstruct missing digits. This synthetic example contains two identifiers and a comma inside a quoted name.

customer_id,name
0012,Asha
9007199254740993,"Dev, Kumar"

3. Preserve values as strings

Paste the example into CSV-to-JSON and choose the comma separator. The converter preserves values as strings and does not automatically infer numbers or dates. The expected records retain the leading zeros and the complete long ID.

[
  {"customer_id":"0012","name":"Asha"},
  {"customer_id":"9007199254740993","name":"Dev, Kumar"}
]

4. Check the saved JSON and receiving system

Download JSON and compare both IDs with the source CSV. Keep identifier fields as strings in the receiving system too: converting a long string back to a JavaScript number can lose precision. Confirm that the receiving schema permits strings. Use unique nonempty headers and the correct separator; fix mismatched row lengths before conversion.