SSL Certificate Decoder
Paste an X.509 certificate in PEM format to read its details in plain language — subject, issuer, validity, SANs, key info and fingerprints. Everything is parsed locally in your browser; your certificate is never uploaded.
New to this? Read the Certificate Decoder guide →
Decoded certificate details will appear here.
Paste a certificate and press Decode.
How to use the certificate decoder
- Paste a PEM certificate (the block that begins -----BEGIN CERTIFICATE-----).
- Press decode to see the human-readable details: subject, issuer, validity dates, key usage and more.
- It runs entirely in your browser, so you can inspect a certificate without sending it anywhere.
The fields that matter
- Subject and SAN. Which names the certificate is valid for. Modern clients check the Subject Alternative Name list, not just the common name.
- Issuer. The certificate authority that signed it, and the chain of trust back to a root.
- Validity (notBefore / notAfter). The window during which it is valid.
- Key usage and extended key usage. What the certificate is allowed to do, such as server authentication.
Red flags to watch for
A certificate that is expired or not yet valid, whose names do not match the host you are visiting, that is self-signed when it should be CA-issued, or that uses a weak signature such as SHA-1, all warrant a closer look. Decoding the certificate yourself shows these details directly rather than trusting a green padlock. Need to renew or reissue? Turn a certificate into a fresh request with the certificate to CSR tool.
Where you'd use this
Checking what a certificate actually contains before or after installing it — the names it covers, when it expires, and whether the chain your server sends is complete.
For example: A site works in Chrome but fails on an Android app. Decoding the served certificate shows it covers example.com but not www.example.com, and the intermediate is missing — desktop browsers fetch it automatically, stricter clients do not.
Frequently asked questions
What does the SSL certificate decoder show?
Paste a PEM certificate to read its details in plain language — subject and issuer, validity dates, serial number, public-key algorithm and Subject Alternative Names.
Can I check when a certificate expires?
Yes. The decoded view shows the "not before" and "not after" dates so you can confirm validity and spot upcoming expiry.
Is my certificate uploaded?
No. Decoding happens entirely in your browser, so even private certificates stay on your machine.