Standardize Phone Numbers in a CSV

Dialers and CRMs want one format. Real lists have a dozen. This example converts a fictional list and shows which numbers a careful tool refuses to touch.

ℹ️ A worked example you can check. The before and after tables below were produced by the free tool on this site from a fictional sample file. Open the same file yourself and you will get the same result.

What Usually Goes Wrong

• US numbers written with brackets, dots, dashes and spaces
• A leading 1 on some numbers and not on others
• Extensions typed as ext. 22, x22 and #22
• International numbers with + or 00
• Seven-digit local numbers with no area code

The Sample File, Before

9 rows of fictional data with the problems above. Every person and company is invented.

Open This File in the Workspace Download the CSV

Standardize Phone Numbers in a CSV sample before cleaning
Name	Phone	Alt Phone	Country
Imani Brooks	(212) 555-0101	212.555.0102	US
Callum Fraser	1-416-555-0103		CA
Yuki Tanabe	+81 3-5555-0104		JP
Sofia Lindqvist	0046 8 555 010 5		SE
Darius Engel	555-0106		US
Renata Coelho	+55 (11) 5555-0107		BR
Miles Abernathy	2125550108 ext. 22	(212) 555-0109 x7	US
Fatima Zahra	212 555 0110	+1 212 555 0111	US
Lucas Moreau	01 55 55 01 12		FR

How to Clean It

1. Keep an untouched copy of the file.
2. Run it with Standardize phone numbers switched on. Both phone columns are picked up from their header names.
3. Read the review list for numbers that were not recognized.
4. For those rows, find the missing area or country code from the Country column or from the contact, and fix them by hand.
5. Export. In the workspace, choose the Excel export if the file will be opened in Excel, so the leading + is kept.

Prefer the command line or an AI agent? The same result comes from smartdata-clean clean phone-formats.csv --phones. See tools for agents.

The Result

9 rows in, 0 removed, 9 out. Ten-digit US and Canadian numbers become +1 followed by ten digits, extensions are kept as x22, and international numbers that start with + or 00 are tidied. The seven-digit number and the French number written in national format are left exactly as they were: without a country code, any conversion would be a guess.

Standardize Phone Numbers in a CSV sample after cleaning
Name	Phone	Alt Phone	Country
Imani Brooks	+12125550101	+12125550102	US
Callum Fraser	+14165550103		CA
Yuki Tanabe	+81355550104		JP
Sofia Lindqvist	+4685550105		SE
Darius Engel	555-0106		US
Renata Coelho	+551155550107		BR
Miles Abernathy	+12125550108 x22	+12125550109 x7	US
Fatima Zahra	+12125550110	+12125550111	US
Lucas Moreau	01 55 55 01 12		FR

What the tool left for you

The tool listed this item for a person to check:

• Phones not recognized, left unchanged: 2 (rows 6, 10)

Checked, not just claimed

The original file, the cleaned file and the change log were run through the separate verifier. Result: PASS.

✓ Removed rows with a valid, verified reason: 0 of 0
✓ Rows: 9 in, 0 removed with a logged reason, 9 out
✓ Cells compared: 36; changed: 10; every change matched to the log: yes
✓ Log entries: 10; not matching the files: 0

The verifier confirms that the change log explains every difference between the two files. It does not judge whether each cleaning choice suits your situation; that part is yours.

The cleaning report

Report text for the sample file

SMARTDATAAI — CLEANING REPORT
Source: phone-formats.csv (fictional practice data)

SUMMARY
Rows in (excluding header): 9
Rows out: 9
Rows removed: 0
Cells changed: 10
  Phones standardized to +E.164: 10

COLUMNS DETECTED
Email: none
Phone: Phone, Alt Phone
Date: none
Name: Name

NEEDS REVIEW
- Phones not recognized, left unchanged: 2 (rows 6, 10)

SAMPLE OF CHANGES (first 10 of 10)
Row 2 · Phone: "(212) 555-0101" → "+12125550101"  [phone]
Row 2 · Alt Phone: "212.555.0102" → "+12125550102"  [phone]
Row 3 · Phone: "1-416-555-0103" → "+14165550103"  [phone]
Row 4 · Phone: "+81 3-5555-0104" → "+81355550104"  [phone]
Row 5 · Phone: "0046 8 555 010 5" → "+4685550105"  [phone]
Row 7 · Phone: "+55 (11) 5555-0107" → "+551155550107"  [phone]
Row 8 · Phone: "2125550108 ext. 22" → "+12125550108 x22"  [phone]
Row 8 · Alt Phone: "(212) 555-0109 x7" → "+12125550109 x7"  [phone]
Row 9 · Phone: "212 555 0110" → "+12125550110"  [phone]
Row 9 · Alt Phone: "+1 212 555 0111" → "+12125550111"  [phone]

Values the tool cannot settle are left as they were and listed above. Where the day/month order of a date was worked out from other dates in the same column, that is listed above too.
Row numbers refer to the original file (header = row 1). Email checks cover format only; they do not confirm that a mailbox exists.

Where a Tool Stops and a Person Starts

Completing local numbers from a country or region column, and validating numbers against a numbering plan, need per-country rules and review. Ask for a quote under Complex Cleanup.

See Service Levels From $19 How We Check Our Work

Standardizing format does not confirm that a number is in service.