Free Tool
Fax Number Validator
Validate fax number formats before sending to avoid transmission failures
Fax Number Validation
Check if your fax number is properly formatted before sending. This tool validates format only, not actual reachability.
This tool only validates number format. It does not test actual connectivity or recipient availability.
How to Validate a Fax Number
Fax number validation checks whether the format complies with international telephone numbering standards. Here's what our tool verifies.
Country Code
Checks for valid international prefix (+33 for France, +1 for USA/Canada, +44 for UK, etc.).
Number Length
Verifies digit count matches the selected country's standards (typically 9-11 digits excluding country code).
Character Validation
Ensures only accepted characters (digits, spaces, dashes, parentheses, plus sign) are present in the number.
E.164 Normalization
Converts to standardized international format (E.164) ensuring universal compatibility across fax services worldwide.
When Fax Number Validation Matters
Real-world scenarios where validating fax numbers before transmission saves time, money, and prevents errors.
New Business Partner
Scenario: Receiving fax number from first-time vendor or client
Challenge: Unclear or incomplete formatting
Solution: Validate before first send to avoid failed transmission and delays
International Faxing
Scenario: Sending faxes to foreign countries
Challenge: Different numbering rules per country
Solution: Confirm proper international format with correct country dial code
Database Migration
Scenario: Importing legacy contact lists with fax numbers
Challenge: Mixed formats from different sources and eras
Solution: Batch validate and normalize all numbers for consistency
Customer Service Entry
Scenario: Customer provides fax number over the phone
Challenge: High risk of transcription errors
Solution: Immediately validate the entered format during call to catch mistakes
5 Best Practices for Fax Numbers
Always store in E.164 format
Use international format (+15551234567) instead of local format ((555) 123-4567) in your databases. This ensures compatibility with all fax services even if you only send domestically today.
Validate before bulk campaigns
For fax broadcasts, check every number on your list before hitting send. A single invalid number can halt the entire batch with some providers, wasting the whole campaign.
Keep normalized versions
Store both the original format clients provide AND the normalized E.164 version. Original format for human readability, normalized for actual transmission – best of both worlds.
Watch out for special numbers
Toll-free numbers (1-800) and most mobile numbers cannot receive faxes. Always verify it's a landline or VoIP line with fax capability before attempting transmission.
Revalidate after service changes
Different fax providers have slightly different format requirements. When switching services, quickly revalidate your frequently-used numbers to catch any compatibility issues early.
Fax Validation FAQ
Does this tool actually test the fax connection?
No, our validator only checks number formatting against international standards. It doesn't dial the number or test whether the line is actually reachable or capable of receiving faxes.
What's the difference between "Valid" and "Possibly Valid"?
"Valid format" means the number passes all rules for the selected country. "Possibly valid" indicates the format looks correct but needs confirmation (for example, if no country was specified with the number).
Why does my working number show as invalid?
Our tool validates against standard international formats, but some carriers accept regional variations. If your number works despite showing "invalid," it likely uses a carrier-specific format accepted locally.
Can I validate a mobile phone number?
Technically yes, but be aware: mobile numbers typically cannot receive faxes. Only landlines (or VoIP services) with fax equipment or virtual fax capability can receive fax transmissions.
What exactly is E.164 format?
It's the international telephone numbering standard: a + symbol, followed by country code, then the national number with no leading zero. Example: +441234567890 for a UK number.
Do I need to remove spaces and dashes first?
No need – our tool automatically strips spaces, dashes, dots, and parentheses. You can paste numbers exactly as provided: +1 (555) 123-4567 or +1.555.123.4567 both work fine.
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