Format check only. This tool validates SSN format structure only. Never enter a real Social Security Number. Use with test or fictional numbers only.
An SSN format validator checks whether a Social Security Number follows the correct 9-digit XXX-XX-XXXX structure, verifies that area, group, and serial numbers are not in known-invalid ranges, and identifies advertising or test SSNs. Designed for developers and data professionals.
Auto-formatted as XXX-XX-XXXX. Validation updates as you type.
Validation Checks
Parsed Breakdown
Validation Rules
Format: Must be exactly 9 digits in XXX-XX-XXXX format.
Area Number (positions 1-3): Cannot be 000, cannot be 666, and cannot be in range 900–999.
Group Number (positions 4-5): Cannot be 00.
Serial Number (positions 6-9): Cannot be 0000.
Known-invalid SSNs: 078-05-1120 (widely published 1938 wallet insert), 219-09-9999 (used in advertising by tax service), and similar demonstration numbers are flagged.
This tool validates format only — it cannot determine if an SSN is actually assigned to a real person.
How to Use the SSN Format Validator
Social Security Numbers follow a strict format defined by the Social Security Administration: nine digits arranged as three groups (XXX-XX-XXXX). Certain combinations within this format are permanently reserved as invalid. This SSN format validator is designed for developers building form validation, QA engineers testing data pipelines, and anyone who needs to verify that a test SSN number follows the correct structural rules.
Step 1: Enter a Test SSN
Type the digits — the tool auto-formats them as XXX-XX-XXXX as you go. You can also paste a pre-formatted SSN with hyphens. The validator starts checking immediately as you type, with full results shown when 9 digits have been entered.
Step 2: Review the Checklist
The pass/fail checklist shows each structural rule: whether the format is correct (9 digits), whether the area number is in a valid range, whether the group and serial numbers are non-zero, and whether the SSN matches any known-invalid demonstration numbers.
SSN Structure Explained
The Area Number (first 3 digits) was originally geographic — assigned to states in numerical order. Today SSNs are assigned randomly, but the invalid ranges (000, 666, 900–999) still apply. The Group Number (digits 4-5) was used to sequence assignments within an area. It cannot be 00. The Serial Number (digits 6-9) is a sequential number within each group. It cannot be 0000. Together these constraints eliminate about 10% of all possible 9-digit combinations from valid use.
Famous Invalid SSNs
The SSN 078-05-1120 was printed on a sample card in wallets sold by Woolworth in 1938, leading thousands of people to use it as their actual SSN. By 1962, over 40,000 people had filed taxes with it. The SSN 219-09-9999 was used in H&R Block advertisements. Both are checked by this validator and correctly flagged as known-invalid test numbers.
FAQ
Is this SSN validator free?
Yes, completely free. No signup, no account needed. All validation runs in your browser with no data sent to any server.
Is my SSN data safe when using this tool?
Yes. This tool runs entirely in your browser using client-side JavaScript. No data is transmitted to any server. However, we strongly recommend only entering test or fictional SSNs — never enter a real SSN into any web tool unless you fully trust the service.
What is this tool designed for?
This tool is designed for developers, testers, and data professionals who need to validate SSN format in test data or applications. It checks format only — not whether an SSN is actually assigned to a real person. Never enter a real SSN.
What are the known-invalid SSN ranges?
Several SSN ranges are permanently invalid: area numbers 000, 666, and 900–999 were never assigned; group number 00 and serial number 0000 are also invalid. Additionally, 078-05-1120 (from a 1938 wallet insert) and 219-09-9999 (used in advertising) are famous invalid SSNs.
What is the SSN area/group/serial structure?
A valid SSN has 9 digits in XXX-XX-XXXX format. The first three digits are the Area Number (originally geographic), the middle two are the Group Number (assigned in a specific sequence), and the last four are the Serial Number (sequential within each group).
Why does this tool auto-format the SSN as I type?
The tool automatically inserts hyphens to format as XXX-XX-XXXX as you type the digits. This makes it easy to visually confirm the structure without needing to type the hyphens yourself.