How to use OpenSSL Certificate Checker
- Give OpenSSL Certificate Checker a PEM certificate to work from.
- Click Parse certificate — OpenSSL Certificate Checker processes everything on your device.
- Review the subject, issuer, validity dates and expiry shown below.
About this tool
There is no server behind OpenSSL Certificate Checker. OpenSSL Certificate Checker decodes a pasted PEM certificate by walking its ASN.1/DER structure locally to read subject, issuer, validity window and serial.
The expiry countdown is computed locally, and nothing about the certificate is transmitted. It behaves the same on desktop and mobile, with nothing stored remotely.
Frequently asked questions
What is OpenSSL Certificate Checker for?
Use OpenSSL Certificate Checker to check your input without installing anything; everything happens client-side.
Does OpenSSL Certificate Checker cost anything?
No — OpenSSL Certificate Checker is completely free, with no sign-up and no hidden limits.
Does OpenSSL Certificate Checker upload my data?
No — OpenSSL Certificate Checker processes everything locally in your browser, so nothing you enter is uploaded or stored.
How do I inspect a live site's certificate in OpenSSL Certificate Checker?
Export the certificate from your browser's padlock as PEM and paste it into OpenSSL Certificate Checker; it decodes the ASN.1/DER fields entirely on your device.
Does OpenSSL Certificate Checker work on mobile?
Yes — OpenSSL Certificate Checker is just a web page and runs on any modern browser, including phones and tablets.