What Is SSL Labs?
Qualys SSL Labs (ssllabs.com) is a free online service that performs deep analysis of SSL/TLS configuration on any public web server. Created by Ivan Ristic, it has become the industry standard for evaluating HTTPS implementations.
When you test a server on SSL Labs, it performs an exhaustive analysis that typically takes 60-90 seconds. The tool probes your server from multiple angles, testing protocol support, key exchange parameters, cipher strength, and certificate chain validity.
SSL Labs is used by security professionals worldwide to validate TLS deployments and is often referenced in compliance audits and security assessments.
What SSL Labs Tests
SSL Labs performs one of the most thorough TLS analyses available:
### Certificate Analysis - Certificate validity and expiration date - Certificate chain completeness (intermediate certificates) - Certificate transparency (CT logs) - Extended Validation (EV) status - Key size (RSA 2048+, ECDSA 256+) - Signature algorithm (SHA-256 minimum) - Subject Alternative Names (SANs) - OCSP stapling support
### Protocol Support - TLS 1.3 (current best) - TLS 1.2 (acceptable) - TLS 1.1 (deprecated, should be disabled) - TLS 1.0 (deprecated, should be disabled) - SSL 3.0 (vulnerable, must be disabled) - SSL 2.0 (critically vulnerable, must be disabled)
### Cipher Suite Analysis - Forward secrecy support - Authenticated encryption (AEAD) ciphers - Weak cipher detection (RC4, DES, 3DES) - Cipher suite ordering - Key exchange strength
### Known Vulnerability Testing - Heartbleed (CVE-2014-0160) - POODLE (CVE-2014-3566) - BEAST (CVE-2011-3389) - ROBOT attack - Ticketbleed - OpenSSL CCS vulnerability - Downgrade attack resistance
### Additional Features - HSTS header presence and configuration - HPKP (deprecated but still checked) - Server signature - Session resumption - ALPN/NPN support
SSL Labs Scores Explained (A+ to F)
SSL Labs calculates a numerical score and maps it to a letter grade:
| Grade | Score Range | Typical Meaning |
|---|---|---|
| A+ | 100% + extras | Perfect TLS config with HSTS |
| A | 80-100% | Strong configuration |
| B | 65-79% | Minor issues (e.g., TLS 1.0 still enabled) |
| C | 50-64% | Moderate issues |
| D | 35-49% | Significant weaknesses |
| E | 20-34% | Serious misconfigurations |
| F | 0-19% | Critical vulnerabilities |
| T | — | Certificate not trusted |
| M | — | Certificate name mismatch |
The score is calculated across four categories: 1. Certificate (30%) — Trust, key strength, algorithm 2. Protocol support (30%) — Which TLS/SSL versions are enabled 3. Key exchange (30%) — Strength of key exchange mechanism 4. Cipher strength (10%) — Strength of the negotiated cipher
An A+ requires not just a high score but also the HSTS header with a long max-age value.
What SSL Labs Doesn't Check
Despite its thoroughness in TLS testing, SSL Labs has a narrow scope. Here's everything it doesn't evaluate:
### HTTP Security Headers Beyond HSTS, SSL Labs doesn't check any security headers. Your Content-Security-Policy, X-Content-Type-Options, X-Frame-Options, Referrer-Policy, and Permissions-Policy configurations are completely ignored.
### Cookie Security
Whether your session cookies have Secure, HttpOnly, and SameSite flags isn't tested. You could have an A+ on SSL Labs while serving session cookies over unencrypted connections.
### Content Security Mixed content (HTTP resources on HTTPS pages), inline scripts vulnerable to XSS, and third-party resource risks aren't analyzed.
### DNS and Email Security SPF, DKIM, DMARC records, and DNSSEC configuration — critical for preventing domain spoofing and phishing — are outside SSL Labs' scope.
### Information Disclosure
Exposed server versions, technology stack fingerprinting, accessible .git directories, and other information leaks aren't checked.
### Application-Level Security CORS misconfigurations, open redirects, clickjacking vulnerabilities, and subresource integrity issues aren't covered.
### Privacy Third-party tracking scripts, analytics configurations, and data collection practices aren't evaluated.
When to Use SSL Labs vs a Full Scanner
Use SSL Labs when: - You're deploying or renewing an SSL certificate - You need to verify TLS protocol configuration after a change - You're debugging a specific TLS handshake issue - A compliance audit requires SSL Labs-specific results - You want to check for known TLS vulnerabilities
Use a full scanner when: - You want to understand your overall website security posture - You're preparing a security report for a client or stakeholder - You need to check headers, cookies, DNS, and content security - You want actionable recommendations across all security areas - You need to track security improvements over time
ZeriFlow vs SSL Labs (Comparison Table)
| Feature | SSL Labs | ZeriFlow |
|---|---|---|
| TLS/SSL analysis | Exhaustive (certificate, protocols, ciphers, vulnerabilities) | Comprehensive (certificate, protocols, HSTS, key strength) |
| HTTP security headers | HSTS only | 11+ headers analyzed |
| Cookie security | No | Yes |
| DNS security | No | Yes (SPF, DKIM, DMARC, DNSSEC) |
| Content security | No | Yes (mixed content, CSP analysis) |
| Information disclosure | Server signature only | Full check (server info, exposed files, fingerprinting) |
| Privacy analysis | No | Yes |
| Performance metrics | No | Yes (Lighthouse integration) |
| Scan speed | 60-90 seconds | Under 60 seconds |
| Score type | Letter grade + numerical | Numerical /100 with category breakdown |
| Recommendations | Minimal | Detailed fix instructions per issue |
| Scan history | No | Yes |
| API access | Yes (but rate-limited) | Yes |
| Price | Free | Free tier available |
Get an A+ TLS Score + Full Security Check
SSL Labs remains an excellent tool for deep TLS analysis. If you need to diagnose a specific certificate chain issue or verify cipher suite ordering, it's the right choice.
But TLS is just one layer of web security. Your headers, cookies, DNS records, and content security matter just as much — and SSL Labs doesn't check any of them.
ZeriFlow gives you the complete picture in a single scan. Check your TLS configuration alongside 12+ other security categories, get a score out of 100, and receive specific fix instructions for every issue.
The free plan lets you scan any website — no signup required for your first scan. See what your SSL Labs grade isn't telling you.