# Ssl Certs

> Manage SSL/TLS certificates and diagnose certificate issues. Use when the user says "cert expiring", "SSL error", "certificate problem", "renew certificate", "check certificate", "HTTPS not working", or asks about TLS/SSL.

- Skill: `majiayu000/ssl-certs` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds add majiayu000/ssl-certs`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/ssl-certs/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/ssl-certs

---


# SSL/TLS Certificates

Manage certificates, diagnose SSL issues, and handle renewals.

## Instructions

1. Identify the issue type (expiring, invalid, chain problem)
2. Use appropriate diagnostic commands
3. Determine root cause
4. Provide remediation steps

## Check certificate expiry

```bash
# Local certificate file
openssl x509 -enddate -noout -in cert.pem

# Remote server
echo | openssl s_client -servername example.com -connect example.com:443 2>/dev/null | openssl x509 -noout -dates

# Check all certs expiring within 30 days
find /etc/letsencrypt/live -name "*.pem" -exec sh -c 'echo "{}:"; openssl x509 -enddate -noout -in "{}"' \;
```

## Certificate information

```bash
# Full certificate details
openssl x509 -text -noout -in cert.pem

# Subject and issuer
openssl x509 -subject -issuer -noout -in cert.pem

# SANs (Subject Alternative Names)
openssl x509 -noout -ext subjectAltName -in cert.pem
```

## Diagnose SSL connection

```bash
# Full connection debug
openssl s_client -connect example.com:443 -servername example.com

# Check specific TLS version
openssl s_client -connect example.com:443 -tls1_2
openssl s_client -connect example.com:443 -tls1_3

# Verify certificate chain
openssl s_client -connect example.com:443 -showcerts
```

## Common issues

| Error | Cause | Solution |
|-------|-------|----------|
| certificate has expired | Cert past end date | Renew certificate |
| unable to verify | Missing intermediate | Add chain certificates |
| hostname mismatch | Wrong cert or missing SAN | Get cert with correct names |
| self-signed certificate | Not from trusted CA | Use Let's Encrypt or commercial CA |

## Let's Encrypt management

```bash
# Check certbot certificates
certbot certificates

# Renew all certificates
certbot renew --dry-run
certbot renew

# Force renewal
certbot renew --force-renewal

# Get new certificate
certbot certonly --nginx -d example.com -d www.example.com
```

## Verify chain

```bash
# Check chain is complete
openssl verify -CAfile chain.pem cert.pem

# Download and verify chain
openssl s_client -connect example.com:443 -showcerts 2>/dev/null | awk '/BEGIN CERTIFICATE/,/END CERTIFICATE/ {print}' > chain.pem
```

## Rules

- MUST check expiry date first for any cert issue
- MUST verify the full certificate chain
- MUST check SANs match the domain being accessed
- Never delete certificates without backup
- Always test with `--dry-run` before certbot renew
- Always reload/restart web server after cert changes