.cer file of your FIEL (now called e.firma) to confirm it is a FIEL and not a CSD, and to read the holder, RFC, CURP when present, serial number, and validity period.
What the FIEL is, and how it differs from the CSD
The FIEL, or e.firma, is the certificate that identifies a taxpayer before the SAT. It is used for filings and to request Certificados de Sello Digital. It does not seal CFDI — that is the CSD’s job. Both certificates arrive as.cer files that are indistinguishable at a glance. The difference lives in the keyUsage extension:
When the FIEL belongs to an individual, its subject usually also carries the holder’s CURP. The tool extracts it when present.
Everything runs in your browser. The certificate is read on your device using native browser APIs. Facturama receives no copy of your certificate and stores no data from it.
Known limits
The .cer and .key pairing is not verified
The .cer and .key pairing is not verified
Confirming that a
.cer and a .key belong together requires decrypting the private key, and SAT keys ship as encrypted PKCS#8, often with 3DES. The browser’s cryptography API (Web Crypto) supports neither 3DES nor importing encrypted PKCS#8, so that check cannot be done client-side.The issuer and revocation status are not validated
The issuer and revocation status are not validated
The tool reads the certificate’s contents, but it does not confirm that the certification authority is really the SAT, nor does it check revocation lists. A self-signed certificate would be read without complaint.
Certificates without the keyUsage extension
Certificates without the keyUsage extension
If the certificate does not include
keyUsage, there is no way to tell a FIEL from a CSD, and the tool says so explicitly instead of guessing. Certificates issued by the SAT always include it.Common errors
Next steps
CSD inspector
Inspect the Certificado de Sello Digital you seal your CFDI with.
CFDI 4.0 XML validator
Verify the structure and seal of an already stamped invoice.