W-9 Validator

What this tool checks

The validator runs structural checks on the fields required by IRS Form W-9:

• EIN structure: Nine digits in the XX-XXXXXXX pattern, with a two-digit prefix drawn from the IRS's published set of campus prefixes. A prefix outside that set indicates a typo or a fabricated number.
• SSN structure: Nine digits in the XXX-XX-XXXX pattern, with area, group, and serial numbers within the ranges defined by SSA randomization rules. Rejects known-invalid values (000, 666, 900-series area numbers used for ITINs when an SSN is claimed).
• Required fields: Legal name, business name (if different), federal tax classification, address, and TIN. Flags a W-9 that is missing any field the IRS requires.
• Entity type consistency: Warns when the tax classification (sole prop, LLC, S-corp, C-corp, partnership) is inconsistent with whether the TIN is an EIN or SSN.

Format checks cannot confirm the IRS has the name/TIN combination on file — that requires IRS TIN Matching, which is restricted to authorized payers. EarnDrift runs the full IRS TIN match automatically on every contractor for paying customers.

Why we built this

About 1 in 20 contractor W-9s arrives with a structurally invalid TIN — usually a transposed digit or a number copied from a sample form. The IRS will reject the 1099, you will get a CP-2100 notice, and you will have to issue a backup-withholding letter. This tool catches the most common errors in the seconds after the W-9 arrives, instead of three months after you file.

Related tools

• All free 1099 tools
• 1099 Threshold Checker — do you owe a 1099?
• NEC vs MISC decision tree
• How to collect a W-9 from a contractor