Certificate Fingerprint API — Free & Private

Free, no signup, runs entirely in your browser — your data never leaves your device.

Compute a fingerprint

curl -G "https://certificate-fingerprint-formatho.filesformatho.workers.dev/api" \
  --data-urlencode "cert=-----BEGIN CERTIFICATE-----
MIIB... your PEM ...-----END CERTIFICATE-----"

Response (excerpt):

{
  "input": { "kind": "pem", "label": "CERTIFICATE", "der_bytes": 466 },
  "fingerprints": {
    "sha256": {
      "hex": "b4053fcb0cf2ba795bc330496fe9a8c0...",
      "colon": "B4:05:3F:CB:0C:F2:BA:79:5B:C3:30:49:..."
    },
    "sha1":   { "hex": "e9701378...", "colon": "E9:70:13:78:..." },
    "sha512": { "hex": "...", "colon": "..." }
  }
}

POST JSON

curl -X POST "https://certificate-fingerprint-formatho.filesformatho.workers.dev/api" \
  -H "Content-Type: application/json" \
  -d '{"cert": "-----BEGIN CERTIFICATE-----..."}'

Both endpoints accept a PEM certificate or its raw base64 DER encoding (fingerprint is computed over the DER bytes exactly like openssl x509 -fingerprint).

Use cases

• Pin a certificate (HPKP-style pinning records, TLSA/SSHFP prep work)
• Verify a cert matches across environments without shipping the cert itself
• Extract pins for Expect-CT / mobile app SSL pinning lists

Clean errors

• Missing/garbled PEM, invalid base64 → 400 with the exact reason
• DER that is truncated or padded → 400 length mismatch message
• Non-certificate PEM labels (e.g. PRIVATE KEY) → still digested, with a warning