Free tool

x.509 Certificate Decoder

Paste an SSL/TLS certificate in PEM format and see issuer, subject, validity, SAN domains, algorithm and SHA-256 fingerprint. 100% in your browser.

Built by

Miguel Ángel Colorado Marin (MACM)

Full-Stack Developer · Guadalajara, España

I develop web apps, digital tools and full projects — from design to deployment.

GitHubLinkedIn
Contact me

How to decode an SSL certificate?

  1. 1

    Copy the PEM certificate

    Get the certificate in PEM format (starts with -----BEGIN CERTIFICATE-----). You can export it from the browser or with openssl.

  2. 2

    Paste it into the tool

    Paste the full block into the text area. Everything is parsed in your browser, the certificate is never uploaded.

  3. 3

    Decode

    Click Decode to see all fields: issuer, subject, validity, SAN, algorithm and fingerprint.

  4. 4

    Check the validity

    An indicator shows whether the certificate is valid, how many days remain or if it's expired.

Frequently asked questions

Is my certificate uploaded to a server?

No. The certificate is parsed 100% in your browser with the node-forge library. It never leaves your device, ideal for internal or private certificates.

What is an x.509 certificate?

It's the standard for the digital certificates used in HTTPS/TLS. It contains the public key, the domain, the issuer (CA), the validity dates and extensions like alternative domains (SAN).

What are SAN domains?

Subject Alternative Names: the list of domains and subdomains the certificate covers. A modern certificate usually secures several domains with this extension.

What is the SHA-256 fingerprint for?

It's a unique identifier of the certificate. It's used to verify a certificate is exactly the expected one (pinning) and to compare it with the one a server presents.

Related tools

SSL Checker

SSL/TLS certificate: issuer, expiry and grade A+→F.

Web Analyzer

Full technical audit: DNS, SSL, SEO, email and stack.

JWT Decoder

Decode JWT tokens instantly.

Hash Generator

MD5, SHA-1, SHA-256 and SHA-512.

Embed Certificate Decoder on your site

Add Certificate Decoder to any web page with a simple iframe. Free, with attribution to miguelacm.es.

<iframe
  src="https://miguelacm.es/embed/certificate-decoder"
  width="100%"
  height="700"
  frameborder="0"
  title="Certificate Decoder — miguelacm.es"
></iframe>
View embed in new tab →