Free tools and guides
Attio CSV phone number cleaner
Clean an Attio CSV phone column to E.164. Keep other columns, review invalid numbers and duplicates, and export locally. Free, with no signup.
Last reviewed: . Free to use. No signup required.
Clean a phone column for Attio
Paste or select a CSV with a header row. Read the file, select its phone column, then clean the numbers. The import file keeps your other columns. The review file keeps rows that need a decision.
A leading + country code takes priority. Use the default country only for numbers without one.
Limit: 1 MiB, 10,000 numbers or CSV data rows, and 100 columns. Use UTF-8 CSV with comma separators and a header row.
Your numbers and CSV data stay in this browser. The tool does not upload or save them. Reloading clears the input.
What goes into each export
| Name | Original phone | E.164 | Export | Reason |
|---|---|---|---|---|
| Alex | (415) 555-0101 | +14155550101 | Attio import | Valid E.164 number |
| Sam | +1 415 555 0101 | +14155550101 | Review file | Same number as record 2 |
| Jo | not a number | — | Review file | Invalid number |
| Lee | +1 212 555 0102 ext. 42 | +12125550102 | Review file | Keep extension 42 in a separate field |
Deduplication keeps the first valid row for a normalized number. It does not combine other fields. Review later rows before deciding whether to merge them. Different people can share a business number.
Extensions do not fit in E.164. Their original values stay in the review file. Add a separate extension attribute or decide how to retain them before import.
Import the cleaned CSV into Attio
- Download both files when review rows exist. Keep your original CSV as a backup.
- Fix invalid numbers and decide what to do with extensions and duplicate records.
- Import the Attio CSV into the correct object or list. Map the chosen column to a phone number attribute. Map a suitable unique attribute, such as email or record ID, to match existing records.
- Use Attio’s Review values and Preview import steps. Confirm the mapping before you start the import.
Attio requires international E.164 phone numbers in its CSV formatting guide. Follow the official CSV import guide for mapping and preview steps. We reviewed both sources on October 8, 2026.
Formula-like source cells receive an apostrophe prefix for spreadsheet safety. Generated E.164 phone cells contain only a plus sign and digits. Import the CSV directly into Attio. Opening and saving it in a spreadsheet can change a phone number’s plus sign or digits. Other column values remain as provided, except the formula safety prefix.
This file cleaner does not validate other Attio attribute formats or change your workspace. See the Attio calling setup guide before building an outbound list.
Related tools and guides
Frequently asked questions
Which phone number format does Attio accept for CSV imports?
Attio's CSV import formatting guide says phone numbers must use international E.164 format. This tool writes the chosen phone column as a plus sign, country code, and digits. Map that column to your phone number attribute in Attio.
Will the cleaner keep my other CSV columns?
Yes. The import CSV keeps the original headers and other fields. Formula-like source cells receive an apostrophe prefix for spreadsheet safety. The tool does not merge names, emails, or other fields from duplicate rows.
What happens to invalid numbers, extensions, and duplicates?
The import file contains valid numbers without extensions. The review file retains the original fields for invalid numbers, numbers with extensions, and removed duplicates. Review and fix those rows separately. Nothing is silently discarded.
How does deduplication work?
When deduplication is enabled, the first valid row for each E.164 number goes into the import file. Later rows with that number go into the review file. Disable it to keep all valid rows. A shared phone number does not prove that two people are the same person.
Does this tool connect to my Attio workspace?
No. It processes your CSV in the browser and creates download files. It does not access Attio or upload your data. You review the file and import it into Attio yourself.
Can I paste a CSV with quoted commas or multiline fields?
Yes. The parser supports comma separators, quoted fields, escaped quotes, CRLF or LF line endings, and a UTF-8 byte order mark. It rejects malformed quotes, duplicate headers, and rows whose field count does not match the header.
Keep your calling work in Attio.
Set up your calling workspace in minutes. Questions about your CRM or team? Talk to us before you start.