TXT works best for plain lists
If each line contains one number, TXT is simple and stable. Remove blank rows and obvious header lines first.
CSV works better for multiple fields
When the file includes source, notes, names, or other columns, CSV is easier to inspect and import.
Test a small sample first
Before processing a full dataset, test around 1,000 rows to confirm column detection and export format.
Reduce noisy symbols
Dashes, spaces, brackets, and country codes are manageable, but headers, comments, and corrupted characters should be removed.
FAQ
Can multiple phone columns be detected?
Automatic scanning can help, but for large files it is safer to confirm the number column.
What if CSV text is garbled?
Save the file as UTF-8 CSV or re-export it from spreadsheet software.
Is XLSX supported?
Spreadsheet support is planned or version-dependent. TXT and CSV remain the safest formats.