SSL憑證檢查工具
檢查任意網域的SSL/TLS憑證：簽發機構、有效期以及距到期的天數。
如何使用本工具
- 1
Type a domain or URL into the input box, for example example.com or https://example.com.
- 2
Click Analyze to open a TLS connection to that host on port 443 and fetch its certificate.
- 3
Read the subject and issuer panels, then check the Valid from, Valid to, and Days remaining boxes.
- 4
Scan the SAN line to confirm the certificate actually covers the hostname you queried.
什麼是SSL憑證檢查工具？
每個HTTPS網站都擁有一份證明伺服器身分的SSL憑證。憑證會過期（Let's Encrypt：每90天；商業憑證：通常每年）。當憑證過期而未續期時，瀏覽器會顯示令人警覺的安全警告。本工具會回報憑證的簽發機構、有效期、剩餘天數以及SAN（主體別名）。
常見使用場景
Confirm a newly issued or renewed certificate is actually live on the server before announcing a launch.
Catch a certificate that is within 30 days of expiry (the tool flags it in red) so you can renew before users hit warnings.
Verify the SAN list includes every subdomain you serve, such as www and api, after editing a multi-domain cert.
Check which Certificate Authority signed a third-party or vendor endpoint you depend on.
Spot-check that an automated renewal job (for example Let's Encrypt via certbot) actually swapped in the new certificate.
Read the exact valid-from and valid-to timestamps when debugging a clock-skew or not-yet-valid certificate error.