SSL Certificate Checker

Overview

An SSL checker API and certificate verification API for expiry monitoring, domain audits and CI checks: send a hostname, get its live SSL certificate back as JSON. SSL Checker opens a real TLS connection to the site, reads the certificate and the chain the server sends, and validates it the way a client does (trusted root, hostname match, expiry), returning the verifier's error code such as CERT_HAS_EXPIRED or UNABLE_TO_VERIFY_LEAF_SIGNATURE when it fails. Alongside issuer, subject, key type, key size and signature algorithm, it reports the TLS protocol and cipher negotiated, the Strict-Transport-Security policy, OCSP stapling and embedded Certificate Transparency SCTs, plus derived checks: days until expiry, an expiring-soon flag and self-signed detection. To see which TLS versions a server still accepts, pair it with TLS Checker.

Live Test SSL Certificate Checker API →

Endpoint

One host, one path per API. The block below shows this call in four languages; every one of them is the same HTTP request. Making requests covers the timeouts, retries and parameter rules that apply to all of them. The SDKs wrap the same call in a typed client.

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curl "https://api.apiverve.com/v1/sslchecker?domain=ebay.com" \
  -H "x-api-key: your_api_key_here"

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const res = await fetch('https://api.apiverve.com/v1/sslchecker?domain=ebay.com', {
  headers: { 'x-api-key': 'your_api_key_here' },
});

if (!res.ok) throw new Error(`${res.status} ${await res.text()}`);

const { data } = await res.json();
console.log(data);

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import requests

res = requests.get(
    "https://api.apiverve.com/v1/sslchecker?domain=ebay.com",
    headers={"x-api-key": "your_api_key_here"},
    timeout=15,
)
res.raise_for_status()

print(res.json()["data"])

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package main

import (
	"fmt"
	"io"
	"net/http"
)

func main() {
	req, _ := http.NewRequest("GET", "https://api.apiverve.com/v1/sslchecker?domain=ebay.com", nil)
	req.Header.Set("x-api-key", "your_api_key_here")

	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()

	out, _ := io.ReadAll(res.Body)
	fmt.Println(string(out))
}

Replace your_api_key_here with the key from your dashboard. When the inputs arrive as a list rather than one at a time, batch requests run up to 200 of them through this same API in a single call.

Authentication

Send your key in the x-api-key header. That is the only auth step — there is no token exchange and no per-endpoint scope to configure. Authentication covers creating, rotating and revoking keys.

Parameters

Sent in the query string. Premium parameters are accepted on every plan but only take effect on plans that include them.

Response

Every API returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape. Response format covers the envelope, the other output formats and how premium fields are withheld.

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{
  "status": "ok",
  "error": null,
  "data": {
    "subject": {
      "C": "US",
      "ST": "California",
      "O": "eBay, Inc.",
      "CN": "ebay.com"
    },
    "issuer": {
      "C": "GB",
      "O": "Sectigo Limited",
      "CN": "Sectigo Public Server Authentication CA OV R40"
    },
    "subjectaltname": "DNS:ebay.com, DNS:befr.ebay.be, DNS:benl.ebay.be, DNS:cafr.ebay.ca, DNS:e-bay.com, DNS:e-bay.it, DNS:ebay.at, DNS:ebay.be, DNS:ebay.ca, DNS:ebay.ch, DNS:ebay.co.nz, DNS:ebay.co.uk, DNS:ebay.com.au, DN…",
    "infoAccess": {
      "CA Issuers - URI": [
        "http://crt.sectigo.com/SectigoPublicServerAuthenticationCAOVR40.crt"
      ],
      "OCSP - URI": [
        "http://ocsp.sectigo.com"
      ]
    },
    "ca": false,
    "bits": 2048,
    "valid_from": "Oct  6 00:00:00 2026 GMT",
    "valid_to": "Apr 22 23:59:59 2027 GMT",
    "serialNumber": "19FD41E42C169CF248511D2BEE660A83",
    "domain": "ebay.com",
    "isExpired": false,
    "isValid": true,
    "daysUntilExpiry": 182,
    "isExpiringSoon": false,
    "isSelfSigned": false,
    "protocol": "TLSv1.3",
    "cipher": "TLS_AES_128_GCM_SHA256",
    "isTrusted": true,
    "trustError": null,
    "hostnameMatches": true,
    "chain": [
      {
        "subject": "ebay.com",
        "issuer": "Sectigo Public Server Authentication CA OV R40",
        "validTo": "Apr 22 23:59:59 2027 GMT",
        "isCA": false
      },
      {
        "subject": "Sectigo Public Server Authentication CA OV R40",
        "issuer": "Sectigo Public Server Authentication Root R46",
        "validTo": "May 13 23:59:59 2040 GMT",
        "isCA": true
      },
      {
        "subject": "Sectigo Public Server Authentication Root R46",
        "issuer": "USERTrust RSA Certification Authority",
        "validTo": "Jan 18 23:59:59 2038 GMT",
        "isCA": true
      },
      {
        "subject": "USERTrust RSA Certification Authority",
        "issuer": "USERTrust RSA Certification Authority",
        "validTo": "Jan 18 23:59:59 2038 GMT",
        "isCA": true
      }
    ],
    "keyType": "RSA",
    "signatureAlgorithm": "sha256WithRSAEncryption",
    "hasEmbeddedSCTs": true,
    "ocspStapled": true,
    "hsts": {
      "present": true,
      "maxAge": 31536000,
      "includeSubDomains": false,
      "preload": false
    }
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Errors

Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change. Error handling covers the full status list and which of them are worth retrying.

Start from a template

A working app built on this API, ready to deploy with your own key. Vercel asks for the key when you deploy; the code is on GitHub to change first.

SSL Certificate Checker

Check whether a site’s SSL certificate is valid and when it expires.

• Python
• Flask

Deploy to VercelSee the template →

Use cases

SSL Monitoring and Expiry Alerts

DevOps teams check their domains daily from a cron job or uptime monitor, alerting on certificates close to expiry, failed chain validation or a hostname mismatch before browsers start showing warnings.

Customer Domain Audits

When clients point custom hostnames to a SaaS platform, automated onboarding scripts verify validity status and key strength before activating traffic.

Certificate Chain and Key Audits

Security teams sweep corporate web properties for setups that need fixing: certificates that fail validation, servers missing an intermediate, RSA keys under 2048 bits, SHA-1 signatures or no HSTS policy.

Partner Domain Verification

To prevent broken checkouts, e-commerce marketplaces inspect partner payment gateways to confirm validity windows before routing shopper transactions.

Other ways to use SSL Certificate Checker

Set up SSL Certificate Checker on APIVerve, or reach the same source a different way. Your APIVerve account and credits work on all of them — one key, one balance.

Related

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