Normalization is not adding a plus sign to any sequence of digits. You need country context, reliable parsing, and a number that is actually plausible.
Store one international format
Store the normalized number with a plus sign, country calling code, and national number, without display punctuation. One reference format prevents the same contact from appearing under several variations.
You may preserve the original input in a separate field for troubleshooting. Deduplication and sending should use the validated normalized value.
Do not guess a country without context
A local number that begins with zero cannot be normalized safely without its country. Use a Country column, the contact group’s country, or an explicit choice during import.
For a multi-country file, require an international prefix or country value on each row. One global assumption can silently turn valid local numbers into the wrong destinations.
Defend against spreadsheet changes
Excel may remove a plus sign, convert a long number to scientific notation, or drop a leading zero. Format the source column as text and inspect the exported file.
During import, accept spaces, parentheses, and dashes as presentation, then remove them before validation. Do not invent digits when a length is inconsistent.
- Read cells as strings.
- Convert 00 only when the remaining international number is valid.
- Add + after identifying the country.
- Reject extensions and stray text.
- Return a specific rejection reason.
Use a phone-number library
Numbering plans differ by country and change over time. A regular expression checks shape, not whether a number is plausible. Use a library maintained from international numbering metadata.
Separate parsing, possibility, and validity. A value may be readable but too short, or have a possible length while not matching a currently assigned range.
Make errors repairable
“Invalid number” does not help someone fix a file. Return the row, original value, country assumption, and type of failure.
Let teams download rejected rows and import only the corrected records. They should not have to repeat a 100,000-contact import to repair a small set of numbers.
