Certificate Inspector
Paste a PEM certificate or drop a .pem / .crt / .cer / .der file and this tool parses the X.509 structure locally, then shows the subject, issuer, validity window and expiry, Subject Alternative Name domains, serial, signature algorithm, whether it is self-signed, and whether it is a CA certificate. No library and no network are involved.
Read the Certificate Inspector guide for what each field means and the common front-desk cases.
Nothing is uploaded. The certificate is parsed in this browser tab and discarded when you reload. This inspects a certificate you provide (paste or drop); it does not fetch a live site's certificate. View source to confirm there are no network calls.
Paste or drop a certificate
Drop a certificate file here (.pem, .crt, .cer, .der), or
.
Parsed: locally, in this browser tab
All parsing is a hand-written DER walker in your browser. No uploads, no lookups, no tracking.
Analysis complete