Is my certificate data sent to a server?

No. The certificate is parsed entirely locally in your browser and is never transmitted over the network.

What file formats does this decoder support?

It supports PEM-encoded text inputs and file uploads with `.pem`, `.crt`, or `.cer` extensions.

Can I decode multiple certificates at once?

No, the tool only parses the first certificate block detected in the input.

How does the tool determine if a certificate is self-signed?

It compares the Subject and Issuer Distinguished Names; if they match, it flags the certificate as self-signed.

Can this tool decode private keys or CSRs?

No, this tool is specifically designed to decode and inspect X.509 public certificates.

X.509 Certificate Decoder | Online Free Tool

Examples

1. Verifying SSL Certificate Expiry and SANs

DevOps Engineer

Background

A DevOps engineer needs to verify if a newly issued SSL certificate contains all the required subdomains in its Subject Alternative Names (SANs) and check its exact expiration date before deploying it to a production load balancer.

Problem

Manually running openssl commands on a local machine to inspect the certificate details is slow and error-prone.

How to use

Paste the PEM-encoded certificate text into the input area.

-----BEGIN CERTIFICATE-----
MIIDdzCCAl+gAwIBAgIQAqyg...
-----END CERTIFICATE-----

Outcome

The tool displays a green 'VALID' status badge, lists the remaining validity days, and displays the full list of domains under the Subject Alternative Names section.

2. Inspecting a Self-Signed Certificate

Security Analyst

Background

A security analyst is reviewing an internal service certificate to confirm it is self-signed and uses a secure signature algorithm.

Problem

Needs to quickly verify the issuer matches the subject and check the signature algorithm without exposing the certificate to external servers.

X.509 Certificate Decoder | Online Free Tool | Elysia Tools

X.509 Certificate Decoder

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Examples

1. Verifying SSL Certificate Expiry and SANs

2. Inspecting a Self-Signed Certificate

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