From the command line (Linux/macOS):

openssl s_client -connect example.com:443 </dev/null 2>/dev/null \
  | openssl x509 -outform PEM

This prints the leaf certificate for any HTTPS host. Paste the full -----BEGIN CERTIFICATE----- … -----END CERTIFICATE----- block above.

Get the full chain (leaf + intermediates):

openssl s_client -showcerts -connect example.com:443 </dev/null 2>/dev/null \
  | sed -n '/-----BEGIN CERTIFICATE-----/,/-----END CERTIFICATE-----/p'

From Chrome / Edge:

1. Navigate to any HTTPS site. Click the padlock icon → Connection is secure → Certificate is valid.
2. In the Certificate viewer, click Details tab → Export…
3. Save as PEM (chain) format. Open in a text editor and paste here.

From Firefox:

1. Click the padlock → Connection Secure → More Information → View Certificate.
2. In the new tab, click PEM (cert) to download, then paste contents here.

Well-known public CA certificates (for quick testing):

• Let's Encrypt root: curl https://letsencrypt.org/certs/isrgrootx1.pem
• Or click Load Sample below to use the ISRG Root X1 certificate.