Read a certificate or CSR without installing openssl

A PEM block or .crt file you can't open locally — drop it in and read the subject, issuer, validity window and SANs directly.

Tools used in this guide

The job

Someone pastes a PEM block into a ticket, or a .crt lands in your downloads folder. Opening it locally means remembering openssl flags — this reads the structure straight in the browser: subject, issuer, serial, validity dates, SANs, key size and signature algorithm.

Drop or paste

PEM text and raw DER both work. Paste the -----BEGIN block into the box or drop the file. Certificates and CSRs are detected separately — a CSR shows the requested subject and extensions instead of validity dates.

Expiry is shown in days remaining, so 'does this cert die next week?' is a one-glance answer.
SANs are listed individually — the multi-host certificate question answers itself.

Limits and trust

Inputs up to 2 MiB parse locally; nothing is uploaded, so it's safe to inspect production certificates. The tool reads structure — it does not verify the chain or revocation. 'Valid dates' does not mean 'trusted'.