100% Client-Side

SSL Certificate Decoder

Decode PEM X.509 certificates — view subject, issuer, validity, and serial

Free Client-Side No Login No Storage
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How to Use the SSL Certificate Decoder

  1. Paste a PEM-encoded certificate (starts with -----BEGIN CERTIFICATE-----).
  2. Click Decode Certificate to extract details.
  3. View subject, issuer, validity dates, serial number, and more.

Uses a lightweight client-side ASN.1 DER parser. No data sent to any server.

What is SSL Certificate Decoder?

PEM (Privacy Enhanced Mail) is a Base64-encoded format used for SSL certificates, private keys, and public keys. A PEM decoder parses these files to reveal the underlying certificate details — validity dates, issuer, subject, and key type.

Common Uses

  • Inspecting SSL certificate expiry dates
  • Verifying certificate chains
  • Debugging TLS handshake issues
  • Confirming a certificate matches its private key

Frequently Asked Questions

What is a PEM Decoder?

PEM (Privacy Enhanced Mail) is a Base64-encoded format used for SSL certificates, private keys, and public keys. A PEM decoder parses these files to reveal the underlying certificate details — validity dates, issuer, subject, and key type.

Why use Aya Corporation's PEM Decoder?

Your private keys and certificates never leave your browser. This is critical — pasting PEM files into unknown online tools exposes your private key infrastructure. Aya Corporation processes everything locally.

When to use this tool

Use when inspecting SSL certificate expiry, verifying certificate chains, debugging TLS handshake issues, or confirming a certificate matches its private key.

Notes from this implementation

Parse the certificate, do not trust the paste

Paste a PEM certificate (the block that starts with BEGIN CERTIFICATE). The script decodes the Base64 body and reads the fields a person usually has to check by hand: subject, issuer, validity dates, subject alternative names, and the signature algorithm. It shows you what the certificate claims. It does not build the chain back to a root you trust, and it does not speak TLS to the host.

A certificate can be well formed and still be the wrong certificate: a lookalike name, a private CA, or a validity window that has not started because your clock is wrong. Use this page to read a PEM a colleague sent you. Use your browser’s padlock, or openssl s_client, when the question is “what is this host serving right now?”

Private keys

If the paste starts with BEGIN PRIVATE KEY or BEGIN RSA PRIVATE KEY, you have the wrong block. Do not drop private keys into a certificate decoder. Clear the box.