SSL Certificate Decoder

Decode PEM-encoded SSL / X.509 certificates in your browser and inspect subject, issuer, SANs, validity dates, algorithms, and fingerprints.

Certificate inputPaste a PEM certificate only. Do not paste a private key.

This is a best-effort decoder. Review production certificates yourself before trusting the result, and only paste public certificates.

Deep dive

More context for SSL Certificate Decoder

Useful when you want to inspect a PEM certificate before you plug it into Nginx, Caddy, or a load balancer.

Overview

What is this tool?

It decodes a PEM-encoded SSL / X.509 certificate locally in your browser and best-effort extracts the subject, issuer, common name, SANs, validity window, algorithms, serial number, and SHA-256 fingerprint.

Input samples

Example inputs

PEM certificate

Typical certificate shape

-----BEGIN CERTIFICATE-----
...base64 body...
-----END CERTIFICATE-----

What to look for

Subject: CN=example.com
Issuer: CN=Example CA
Not Before / Not After: validity window
SANs: DNS names and IP addresses

When to use it

Common use cases

Check which hostnames a certificate is valid for before you deploy it.
Compare the issuer, algorithms, and fingerprint when you are auditing TLS setup.
Confirm whether a certificate is expired or close to expiring before you wire it into a proxy.

Navigation

Explore related workflows

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Part of collection

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Security Header & Certificate Tools

Browser-based helpers for checking security headers, decoding certificates, reviewing CSRs, and spotting risky web configuration patterns.

Related workflow

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Answers

FAQ

Is this a full certificate validator?

No. It is a best-effort decoder that focuses on the fields most people need to inspect quickly.

Should I still verify production certificates elsewhere?

Yes. Always confirm production TLS settings with your server, CA, or deployment process before you trust the result.

Can I paste a private key here?

No. Only paste the public certificate. Never paste a private key into the tool.

What should I check after decoding the certificate?

Match the subject and SANs to your domain, confirm the issuer and expiry, then verify the live response headers and proxy configuration.

Disclaimer

Disclaimer / limitation note

This tool is a best-effort certificate decoder, not a replacement for production validation. Always confirm live TLS settings yourself before you rely on them. Do not paste a private key into the page; paste only the public certificate. All parsing happens locally in your browser and is not uploaded to a server.

Privacy

Privacy note

Decoding happens entirely in your browser. No backend request is needed, no login is required, and DevToolkit does not store the certificate content you paste here.