How to verify a business by EIN with an API

An EIN (Employer Identification Number) is the IRS tax ID for a U.S. business. KnowFirm lets you verify a business by its EIN in a single API call and resolve it to a canonical entity linked across sources (GLEIF LEI, SEC CIK, FDIC, and more).

One call

curl -H "X-API-Key: $KNOWFIRM_KEY" \
  "https://api.knowfirm.com/v1/business?ein=12-3456789"

Response (shape)

{
  "resolvedEntityId": "name:acmecorporation",
  "canonicalName": "ACME CORPORATION",
  "subjectType": "company",
  "identifiers": { "ein": "12-3456789", "lei": "…", "cik": "…" },
  "sourceIds": ["irs_exempt", "gleif", "sec"],
  "confidence": 85,
  "firmographics": { "addressFull": "…", "state": "…" },
  "provenance": { "ein": ["irs_exempt"], "lei": ["gleif"] }
}

Why resolve, not just look up?

A raw EIN lookup gives you one record. KnowFirm merges every source that refers to the same business (via shared strong identifiers) into one entity, so you get the LEI, CIK, address, and a confidence score — not just the IRS row. Each field carries its source in provenance.

Notes

• Returns 404 if no business matches the EIN.
• KYB/firmographic use only — not for credit, employment, insurance, or housing eligibility (not FCRA).

See also: KYB API overview · Quickstart.