Certificates

Decode an X.509 certificate or chain

POSThttps://ecdsa.com/api/v1/cert/decode

Accepts PEM (one or more CERTIFICATE blocks — a whole chain works) or a single DER certificate as base64/hex. Returns a structured summary per certificate — subject, issuer, validity, key and signature algorithms, SAN, key usage, fingerprint — plus assessments (weak hashes, expiry, CA/Browser Forum lifetime limits, post-quantum notes).

API key: Optional; a key needs the scope api
Quota cost with a key: 1 unit per call
Rate limit: 60 requests/min per IP

Request

JSON body: CertDecodeRequest

Field	Type	Required	Description
certificate	string	yes	PEM with one or more CERTIFICATE blocks (chains welcome), or one DER certificate as base64/hex.

Responses

200Decoded certificates with assessments.

Field	Type	Required	Description
certificates	CertificateSummary[]	yes
notes	string[]	yes	Per-block problems and skipped-block notes.

Headers: X-Request-Id · X-RateLimit-Limit · X-RateLimit-Remaining · X-RateLimit-Reset · X-Quota-Limit · X-Quota-Remaining · X-Quota-Reset

Status	Meaning	Codes
400	Bad request. Input limits: a request body of at most 100 KB (a larger one is answered with 413) and arrays and objects nested at most 64 levels deep, JSON documents inside string fields included.	invalid_json missing_field invalid_input private_key_rejected
401	Unauthorized.	unauthorized
403	Forbidden.	forbidden_scope
404	Not found.	not_found
405	Method not allowed.	method_not_allowed
413	Payload too large.	payload_too_large
429	Too many requests.	rate_limited quota_exceeded
500	Internal server error.	internal_error
503	Service unavailable.	service_unavailable
504	Gateway timeout.	timeout

Every error answer carries the JSON envelope; the error table says what each code means and what to do.

Example

A self-signed ECDSA P-256 certificate

curl

curl -sS 'https://ecdsa.com/api/v1/cert/decode' \
  -H 'content-type: application/json' \
  -d '{
  "certificate": "-----BEGIN CERTIFICATE-----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\n4v4zJDEFLZ5reA==\n-----END CERTIFICATE-----"
}'

JavaScript (fetch)

const response = await fetch("https://ecdsa.com/api/v1/cert/decode", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "certificate": "-----BEGIN CERTIFICATE-----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\n4v4zJDEFLZ5reA==\n-----END CERTIFICATE-----"
  }),
});
console.log(response.status, await response.json());

Python (httpx)

import httpx

response = httpx.post(
    "https://ecdsa.com/api/v1/cert/decode",
    json={
        "certificate": "-----BEGIN CERTIFICATE-----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\n4v4zJDEFLZ5reA==\n-----END CERTIFICATE-----",
    },
    timeout=30.0,
)
print(response.status_code, response.json())

Response 200

{
  "certificates": [
    {
      "subject": "CN=demo.ecdsa.com, O=ECDSA.com Signature Lab, C=US",
      "issuer": "CN=demo.ecdsa.com, O=ECDSA.com Signature Lab, C=US",
      "selfSigned": true,
      "serialNumber": "04:a1:b2:c3:d4:e5:f6:07",
      "version": 3,
      "notBefore": "2026-01-15T00:00:00.000Z",
      "notAfter": "2027-01-15T00:00:00.000Z",
      "validityStatus": "valid",
      "daysRemaining": 87,
      "lifetimeDays": 365,
      "publicKeyLabel": "ECDSA P-256",
      "signatureLabel": "ecdsa-with-SHA256",
      "san": [
        "DNS:demo.ecdsa.com",
        "DNS:www.demo.ecdsa.com"
      ],
      "keyUsage": [
        "digitalSignature"
      ],
      "extendedKeyUsage": [
        "serverAuth",
        "clientAuth"
      ],
      "basicConstraints": {
        "ca": false
      },
      "subjectKeyId": "e9:10:bd:14:b6:ed:51:f2:ac:c7:67:d2:16:0b:65:8f:ef:cf:65:a9",
      "authorityKeyId": null,
      "fingerprintSha256": "54:7A:73:8B:31:CE:3A:55:54:58:4B:5C:FD:D8:CE:7F:78:B7:05:15:29:A3:B7:D5:38:FA:3D:A7:93:5E:C2:CA",
      "assessments": [
        {
          "kind": "info",
          "title": "Classical algorithm — post-quantum migration ahead",
          "body": "ECDSA P-256 (≈128-bit classical security) is a sound choice today. It is, however, quantum-vulnerable: NIST IR 8547 (draft) plans to disallow classical signature algorithms — ECDSA, EdDSA and RSA — after 2035. At this key size there is no earlier 2030 milestone — that step applies only to 112-bit parameter sets such as RSA-2048. No emergency — but worth an inventory: our upcoming repository scanner maps where your systems still sign with classical algorithms and the matching post-quantum migration targets."
        },
        {
          "kind": "ok",
          "title": "Within validity period",
          "body": "Valid until 2027-01-15 00:00:00 UTC — 87 days remaining."
        }
      ]
    }
  ],
  "notes": []
}

The API’s answer to this example, produced for this page on October 20, 2026; relative times and day counts in it refer to that day.

Error codes

Code	Status	Meaning
invalid_json	400	The body is not valid JSON or not a JSON object; or the input nests arrays and objects more than 64 levels deep (JSON documents inside string fields count too), or is too complex to inspect for private keys.
missing_field	400	A required field is absent or empty.
invalid_input	400	A field could not be parsed — the message explains exactly why.
private_key_rejected	400	The request contains private-key material (a PEM PRIVATE KEY block, an OpenSSH, SSH2 or PuTTY private key, or a JWK with "d"). Never send private keys anywhere.
unauthorized	401	The Authorization or X-API-Key header is malformed, the API key is not valid (wrong checksum, unknown, revoked or expired), or the operation needs a key.
forbidden_scope	403	The API key is valid but lacks a scope this operation requires; the message names it.
not_found	404	No operation exists at this path.
method_not_allowed	405	The path exists but does not accept this HTTP method; see the Allow header.
payload_too_large	413	The body exceeds 100 KB.
rate_limited	429	Too many requests — see Retry-After.
quota_exceeded	429	A daily or monthly quota of the API key's account is used up. X-Quota-Reset (and Retry-After) say when it starts over; retrying earlier cannot succeed.
internal_error	500	Unexpected server error.
service_unavailable	503	API keys cannot be verified right now (the key store is unreachable); retry shortly.
timeout	504	The operation did not finish within its time budget.

Schemas

CertificateSummary

Field	Type	Required	Description
subject	string	yes
issuer	string	yes
selfSigned	boolean	yes	Subject and issuer are identical.
serialNumber	string	yes	Colon-separated hex.
version	integer \| null	yes
notBefore	string	yes	format date-time
notAfter	string	yes	format date-time
validityStatus	string	yes	one of "valid", "expiring", "expired", or "not-yet-valid"
daysRemaining	integer	yes	Days until notAfter (zero or negative once expired).
lifetimeDays	integer	yes
publicKeyLabel	string	yes
signatureLabel	string	yes
san	string[]	yes	"DNS:example.com" style Subject Alternative Name entries.
keyUsage	string[]	yes
extendedKeyUsage	string[]	yes
basicConstraints	object \| null	yes
basicConstraints.ca	boolean	yes
basicConstraints.pathLength	integer	no
subjectKeyId	string \| null	yes
authorityKeyId	string \| null	yes
fingerprintSha256	string	yes	Colon-separated uppercase hex SHA-256 of the DER.
assessments	CertificateAssessment[]	yes

CertificateAssessment

Field	Type	Required	Description
kind	string	yes	one of "ok", "err", "warn", or "info"
title	string	yes
body	string	yes

Error

The error envelope of every non-2xx response.

Field	Type	Required	Description
error	object	yes
error.code	string	yes	Machine-readable error code. Each response lists the codes it can carry; new codes may be added within v1, so treat an unknown code by its HTTP status.
error.message	string	yes	Human-readable explanation (English).
error.requestId	string	no	The X-Request-Id of this request — quote it when reporting a problem. Sent since v1.1.
error.detail	object	no	Structured context for the error, such as the offending field; omitted when there is none. any member names
error.docs	string	no	Where the error codes are explained. Sent since v1.1. format uri

All operations are listed in the API reference.