Certificate Decoder

Paste a PEM-encoded X.509 certificate to inspect metadata. PEM format only — DER/base64 and certificate chains show the first certificate. Read-only — private keys are never extracted.

  • Runs entirely in your browser
  • No data stored or sent to a server
  • Free forever — no signup
  • Instant conversion

Input and Output

Use the interactive encoder and decoder on this page to process your text.

Learn more about Certificate decoding

How to Decode X.509 Certificates

Certificate Decoding

When to Decode Certificates

Inspect TLS certificates from servers, decode PEM blocks from config files, or verify subject, issuer, validity dates, and SAN entries during SSL troubleshooting. Paste a PEM-encoded certificate to see parsed fields without openssl on the command line.

Supported Input Formats

Paste PEM certificates wrapped in -----BEGIN CERTIFICATE----- headers. PEM only — DER or raw base64 is not supported. If multiple certificates are pasted, the first is decoded. The decoder extracts common name, organization, serial number, validity window, signature algorithm, and Subject Alternative Names.

Developer Tips

  • Compare expiry dates before certificate rotation incidents
  • Verify SAN entries cover all domains your service serves
  • CLI equivalent: openssl x509 -in cert.pem -text -noout

Frequently asked questions

Is my certificate sent to a server?

No. Decoding runs entirely in your browser. Clear the page after inspecting sensitive certificates on shared machines.

Can I decode private keys?

This tool focuses on X.509 certificates. Private keys require separate handling and should never be shared or pasted on untrusted pages.