About SSL Certificate Checker
Our SSL Certificate Inspector examines your target HTTPS endpoint in real time. It audits the certificate issuer (e.g. Let's Encrypt, Cloudflare, DigiCert, Sectigo), Subject Alternative Names (SANs), signature algorithm (e.g. SHA-256 with RSA), TLS protocol support (TLS 1.2, TLS 1.3), and exact days remaining before expiration.
Mathematical Formula & Calculation Method
TLS Handshake & Chain of Trust: Root CA → Intermediate CA → Leaf/Server Certificate
The client validates that the leaf certificate is signed by an intermediate certificate which chains to a trusted root certificate pre-installed in the browser/OS trust store.
| Variable | Definition / Parameter | Unit |
|---|---|---|
Validity Period |
Start date and expiry date of certificate | Days / Date |
Issuer (CA) |
Certificate Authority that cryptographically signed the cert | Organization |
SANs |
Subject Alternative Names covered by the certificate | List of Domains |
Cipher Suite |
Key exchange, encryption, and MAC algorithms | Protocol Spec |
Step-by-Step Calculation Examples
SSL Expiration & Health Audit
Scenario: Auditing TLS security and remaining validity days for secure checkout.
- Target Host: example.com
- Port: 443
OpenSSL TLS 1.3 Handshake & X.509 Certificate Chain Inspection
How to Use the SSL Certificate Checker
- Enter any website hostname or URL (e.g. google.com).
- Click "Check SSL".
- View validity dates, days remaining, certificate authority (CA), and Subject Alternative Names (SANs).
Common Real-World Use Cases
Prevent Certificate Expiry Outages
Monitor production website certificates to renew them before browser "Not Secure" warning screens appear.
Verify Multi-Domain SAN Coverage
Ensure all subdomains (www, api, app) are covered under Wildcard or multi-domain certificates.
TLS Protocol Hardening
Confirm that deprecated protocols (SSLv3, TLS 1.0, TLS 1.1) are disabled in favor of TLS 1.2 and TLS 1.3.
Key Features & Capabilities
- Calculates exact days and hours remaining until SSL expiration.
- Verifies Certificate Authority (Let's Encrypt, DigiCert, Cloudflare, etc.).
- Lists all covered Subject Alternative Names (wildcards and subdomains).
Technical Architecture & Privacy
SSL Certificate Checker is engineered with a focus on performance, mathematical accuracy, and maximum user privacy. Operating with a high-performance, rate-limited backend infrastructure, this utility delivers real-time network diagnostics and deep protocol analysis backed by strict SSRF filtering and automated sanitization.