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TLS Certificate Decoder

Paste a PEM certificate to read its issuer, subject, validity, key details, alternative names and SHA fingerprints.

Decode a certificate

Paste a PEM certificate to begin.
Certificate size: 0 bytes
Days remaining: -
Parsing happens entirely in your browser: the PEM text never leaves your device.

How to use the TLS Certificate Decoder

  1. Paste a PEM certificate, including the BEGIN and END CERTIFICATE lines.
  2. Click Decode to walk the ASN.1 structure and read every field.
  3. Check the dates, subject, key size, names and fingerprints before copying the fields.

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Frequently Asked Questions

Common questions about the free online tls certificate decoder.

It is Base64 text wrapped between BEGIN CERTIFICATE and END CERTIFICATE lines that encodes a DER certificate.
Paste the PEM text and click Decode. The tool reads the fields locally and never sends the input anywhere.
The version, serial number, signature algorithm, issuer, subject, validity dates, public key, alternative names and fingerprints.
Yes. The tool compares the not-after date with your current clock and reports the days remaining or how long ago it expired.
The decoder reads the first certificate block, so split a bundle and paste the certificate you want to inspect on its own.
SHA-1 and SHA-256 digests of the raw DER bytes are shown as lowercase hex strings using the browser's own digest function.
No. The Base64 is decoded and parsed in your browser, so the certificate text never leaves your device.
A few browsers expose no digest API in insecure contexts, so the parser still reports every field but leaves the digests out.
No. Validity dates are normalised to UTC so they match the certificate and stay consistent wherever you are.
Yes. It is free and unlimited, needs no account, and runs on desktop and mobile browsers alike.

Last updated: October 10, 2026