Frequently Asked Questions
Answers to common questions about the tool, E.164 format, and phone data handling.
New here? Start with the homepage tool, read what E.164 format means, or try the sample CSV before using your real data.
What is E.164 format?
E.164 is the international telephone numbering plan. It ensures every device has a globally unique phone number. The format is a plus sign (+) followed by the country code and the subscriber number, without any spaces, dashes, or formatting characters. Most modern CRMs and APIs require this format.
Does my file leave my computer?
No. All processing happens entirely within your web browser using JavaScript. We do not upload your CSV file or its contents to any server. Your data remains completely private on your device.
What if my CSV has numbers from many countries?
If your CSV includes a country column (e.g. "US", "GB", "DE"), map that column in the configuration step. The tool will read the country code per row to accurately format local numbers. Numbers already starting with "+" are handled regardless of the country setting.
What does "Needs Review" mean?
A row is flagged as "Needs Review" when the phone field contains data the tool cannot confidently normalize automatically. This usually happens when the field contains extensions (e.g. "x123"), notes, or multiple numbers separated by commas. Download these rows separately to clean them manually.
Why was a number marked invalid?
A number is marked invalid if it fails structural rules. This usually means the number is too short (fewer than 7 digits), too long (more than 15 digits), or the combination of country code and subscriber number does not correspond to any valid numbering plan according to libphonenumber.
Does the tool support CSV files only?
Currently, yes. For files in Excel (.xlsx) or Numbers formats, use "Save As" or "Export to CSV" before uploading.
What happens to numbers with extensions?
E.164 does not formally support extensions. When the tool detects an extension (via "ext", "x", or "#"), it flags the row as "Needs Review". You should separate the extension into a different column in your CRM if required.
How do I handle local numbers without country codes?
Provide a "Default Country" in the configuration step. When the parser encounters a local number (like "555-0198") without an international prefix, it will assume the number belongs to the default country you selected.