How to Check SSL Certificate Expiry for Domains Using Node.js (Nodemailer, TLS)

In this blog, I’ll walk you through how to:
✅ Check SSL certificate status for multiple domains using Node.js.
✅ Automate expiry detection to avoid manual checks.
✅ Send email notifications to admins when a certificate expires, using Nodemailer.

By the end of this tutorial, you’ll have a complete solution to monitor SSL certificates and receive alerts before they expire. Let’s dive into the code! 

Prerequisites

Before diving into the code, ensure you have:
1️⃣ Node.js installed on your system.
2️⃣ A GoDaddy, Gmail, or any SMTP email account to send alerts.
3️⃣ A list of domains you want to monitor.

Step-by-Step Guide to Implement SSL Expiry Checker in Node.js

1️⃣ Install Required Packages

To begin, create a project directory and initialize a Node.js project:

mkdir ssl-monitor && cd ssl-monitor

npm init -y

Next, install the required dependencies:

npm install nodemailer dotenv

• nodemailer – Sends email notifications.
• dotenv – Loads environment variables securely.

2️⃣ Set Up Environment Variables

Create a .env file to store sensitive credentials:

SMTP_HOST=smtp.your-email-provider.com

SMTP_PORT=465

SMTP_USER=your-email@example.com

SMTP_PASS=your-email-password

NOTIFY_EMAIL=admin@example.com

• Replace SMTP_HOST, SMTP_USER, and SMTP_PASS with your SMTP provider details.
• Set NOTIFY_EMAIL as the email where alerts will be sent.

3️⃣ Write the SSL Expiry Checker Script

3.1 Import Required Modules

const tls = require("tls");

const nodemailer = require("nodemailer");

require("dotenv").config(); // Load environment variables

• tls module allows us to establish a secure connection to check SSL certificates.
• nodemailer sends email alerts.
• .env configuration is loaded for security.

3.2 Define Domains to Monitor

const domains = ["example.com", "yourwebsite.com", "expired.badssl.com"];

let expiredDomains = [];

• Replace the domain names with your list of domains.
• We store expired domains in expiredDomains[].

3.3 Function to Check SSL Expiry

function checkSSLCertificate(domain) {

    return new Promise((resolve) => {

        const options = { host: domain, port: 443, servername: domain };

 

        const socket = tls.connect(options, () => {

            const cert = socket.getPeerCertificate();

            if (!cert || !cert.valid_to) {

                console.log(`⚠️ Could not retrieve SSL certificate for ${domain}`);

                resolve({ domain, expired: true, expiryDate: "Unknown" });

                socket.destroy();

                return;

            }

 

            const expiryDate = new Date(cert.valid_to);

            const today = new Date();

            const isExpired = expiryDate < today;

 

            socket.end();

            resolve({ domain, expiryDate, isExpired });

        });

 

        socket.on("error", () => {           

            resolve({ domain, expired: true, expiryDate: "Unknown" });

        });

    });

}

✅ What This Function Does:

• Establishes a secure TLS connection to check the SSL certificate.
• Extracts the certificate’s expiration date.
• Returns whether the certificate is expired or valid.
• Handles errors gracefully if the domain has no SSL or cannot be reached.

3.4 Function to Send Email Notifications

async function sendNotification(expiredDomains) {

    if (expiredDomains.length === 0) return; // No expired domains, no email needed

 

    const transporter = nodemailer.createTransport({

        host: process.env.SMTP_HOST,

        port: process.env.SMTP_PORT,

        secure: true,

        auth: {

            user: process.env.SMTP_USER,

            pass: process.env.SMTP_PASS,

        },

        tls: {

            minVersion: "TLSv1.2"

        },

    });

 

    let mailOptions = {

        from: process.env.SMTP_USER,

        to: process.env.NOTIFY_EMAIL,

        subject: "🚨 SSL Certificate Expiry Alert",

        text: `The following domains have expired SSL certificates:\n\n${expiredDomains.join("\n")}`,

    };

 

    try {

        await transporter.sendMail(mailOptions);

        console.log("✅ Notification sent successfully!");

    } catch (error) {

        console.error("❌ Error sending notification:", error);

    }

}

✅ What This Function Does:

• Uses Nodemailer to send an email alert to the admin.
• Includes a list of expired domains in the email.
• If there are no expired SSLs, it skips sending an email.

3.5 Check All Domains & Trigger Notifications

async function checkAllDomains() {

    console.log("🔍 Checking SSL certificates...\n");

 

    for (let domain of domains) {

        const result = await checkSSLCertificate(domain);

        console.log(`✅ ${result.domain} - Expiry Date: ${result.expiryDate}`);

 

        if (result.isExpired) {

            console.log(`❌ ALERT: SSL Expired for ${result.domain}`);

            expiredDomains.push(`${result.domain} (Expired on ${result.expiryDate})`);

        }

    }

 

    // Send notification if expired SSLs are found

    if (expiredDomains.length > 0) {

        await sendNotification(expiredDomains);

    } else {

        console.log("✅ All SSL certificates are valid.");

    }

}

 

// Run the script

checkAllDomains();

✅ What This Function Does:

• Loops through all domains and checks their SSL expiry.
• Logs valid and expired SSL certificates to the console.
• Triggers email notification if any expired certificates are found.

Testing the Script

Run the script using:

node ssl-checker.js

If an SSL is expired, an email notification is sent to the admin.

🎯 Conclusion

With this Node.js SSL monitoring script, you can:
✅ Automate SSL certificate checks across multiple domains.
✅ Prevent website downtime by identifying expired certificates early.
✅ Receive email alerts when SSL certificates expire.

This solution ensures that you never miss an SSL expiry again!