How to use OpenSSL Checker
- Add a PEM certificate to OpenSSL Checker to get started.
- Click Parse certificate — OpenSSL Checker processes everything on your device.
- Read the subject, issuer, validity dates and expiry that OpenSSL Checker lays out for you.
About this tool
Everything OpenSSL Checker does happens on your own device. OpenSSL Checker decodes a pasted PEM certificate by walking its ASN.1/DER structure locally to read subject, issuer, validity window and serial.
To check a live site, export its certificate from the browser padlock as PEM and paste it here. No data is sent anywhere, so it stays fast and private by default.
Frequently asked questions
How do I use OpenSSL Checker?
OpenSSL Checker lets you check your input right in the browser, with the result shown instantly and nothing uploaded.
Is OpenSSL Checker free to use?
Yes — OpenSSL Checker is completely free, with no usage limits.
Does OpenSSL Checker upload my data?
No — OpenSSL 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 Checker?
Export the certificate from your browser's padlock as PEM and paste it into OpenSSL Checker; it decodes the ASN.1/DER fields entirely on your device.
Does OpenSSL Checker work on mobile?
Yes — OpenSSL Checker is just a web page and runs on any modern browser, including phones and tablets.