Certificate SAN Checker
Check Subject Alternative Names and wildcard certificates.
- Enter a hostname to fetch a live certificate, or paste a certificate PEM.
- Click Check SANs.
- Review Common Name, SANs list, certificate type, and validity.
-----BEGIN CERTIFICATE-----\nMIIFazCCA1OgAwIBAgIR...\n-----END CERTIFICATE-----
What are Subject Alternative Names (SANs)?
Subject Alternative Names (SANs) are extensions in SSL certificates that allow a single certificate to secure multiple domain names. Instead of purchasing separate certificates for each domain, SANs enable one certificate to protect multiple hostnames, subdomains, and even different domains entirely.
SANs are essential for modern web applications that serve content across multiple domains, subdomains, or need to support both www and non-www versions of a website. They provide flexibility, cost savings, and simplified certificate management.
Why Check Certificate SANs?
🔍 1. Verify Domain Coverage
Ensure your certificate covers all necessary domains:
- → Primary Domain: Main website domain (example.com)
- → WWW Variant: Both www.example.com and example.com
- → Subdomains: api.example.com, mail.example.com
- → Additional Domains: Multiple brand domains
⚠️ 2. Prevent SSL Errors
Missing SANs cause browser security warnings:
- "Certificate name mismatch" errors
- "This site is not secure" warnings
- Mixed content warnings on HTTPS pages
- API calls failing due to certificate errors
- User trust issues and abandonment
💰 3. Cost Optimization
SAN certificates provide significant cost savings:
- One certificate instead of multiple individual certificates
- Reduced administrative overhead
- Simplified renewal processes
- Lower total cost of ownership
- Bulk pricing advantages
🔧 4. Certificate Management
Simplify certificate operations:
- Single certificate to install and manage
- Synchronized expiration dates
- Consistent security policies
- Easier compliance auditing
Types of SAN Certificates
🌐 Multi-Domain SAN
Secures multiple different domains:
- • example.com
- • mybrand.com
- • company.org
- • Up to 100+ domains
🔗 Subdomain SAN
Covers multiple subdomains:
- • www.example.com
- • api.example.com
- • mail.example.com
- • cdn.example.com
🌟 Wildcard SAN
Combines wildcard and specific domains:
- • *.example.com
- • example.com
- • anotherdomain.com
- • Unlimited subdomains
Common SAN Use Cases
🏢 Corporate Websites
Secure main website and related services:
- company.com and www.company.com
- blog.company.com for content marketing
- support.company.com for customer service
- shop.company.com for e-commerce
🔌 API Services
Secure multiple API endpoints:
- api.example.com for main API
- api-v2.example.com for version 2
- webhooks.example.com for callbacks
- cdn.example.com for static assets
🛒 E-commerce Platforms
Protect customer data across domains:
- store.example.com for main shop
- checkout.example.com for payments
- account.example.com for user profiles
- admin.example.com for management
☁️ Cloud Applications
Secure distributed cloud services:
- app.example.com for main application
- dashboard.example.com for analytics
- files.example.com for document storage
- mail.example.com for email services
💡 SAN Certificate Best Practices
- ✓ Plan all domains before certificate purchase
- ✓ Include both www and non-www versions
- ✓ Consider future subdomain requirements
- ✓ Use wildcard SANs for dynamic subdomains
- ✓ Verify SAN coverage before going live
- ✓ Monitor certificate expiration across all SANs
- ✓ Test all domains after certificate installation
Troubleshooting SAN Issues
❌ Domain Not Listed in SANs
Problem: Browser shows certificate name mismatch error.
Solution: Add the domain to certificate SANs or obtain a new certificate that includes the missing domain.
❌ Wildcard Not Covering Subdomain
Problem: Wildcard certificate doesn't work for specific subdomain.
Solution: Wildcard certificates only cover one level (*.example.com covers api.example.com but not sub.api.example.com). Add specific subdomains to SANs.
❌ SAN Limit Exceeded
Problem: Need to secure more domains than SAN certificate allows.
Solution: Upgrade to higher SAN limit certificate or use multiple certificates with load balancing.
🔗 Related Tools
Complete your certificate management workflow: