How to read a .CER file online
Three steps, a few seconds.
Open your .CER file
Drop it on the box or click to choose it. A bundle holding several certificates is split for you automatically.
Unlock if needed
A password-protected file asks for its export password. It is used only to unlock the file.
Check the details
Read the chain from your certificate up to the root, see every domain it covers, when it expires and copy its SHA-256 fingerprints.
What is a .CER file?
What's inside .crt, .pem and .p12 files, in plain words.
A CER file is an X.509 digital certificate that binds an identity (a website, server, or publisher) to a public key, signed by a Certificate Authority. On Windows, double-click it to view the issuer, validity dates, and purpose, then install it into the certificate store if needed. It holds a public key only and is safe to share.
Programs that open .CER files
| Full name | Security certificate (X.509 .cer) |
|---|---|
| Developer | ITU-T / IETF (X.509 PKI standard); the .cer convention is common on Windows |
| First released | X.509 first published 1988; .cer is a long-standing Windows certificate extension |
| Category | Data & Other |
| MIME type | application/x-x509-ca-cert |
| Signature | 30 82 (DER-encoded .cer starts with ASN.1 SEQUENCE: 0x30 0x82 . PEM-encoded .cer starts with text '-----BEGIN CERTIFICATE-----') |
Related viewers
Other free tools to open and preview your files.
Frequently asked questions
Is it safe to open my .CER file here?
Yes. Certificates are public by design, and decoding and signature checks run with the Web Crypto API.
What does “chain verified” mean?
Each certificate is signed by the one above it. The viewer checks those signatures mathematically, so you can see whether your server certificate, intermediate and root actually belong together - the most common cause of “incomplete chain” errors.
My .p12 / .pfx asks for a password. Which one?
The password chosen when the file was exported (for example from Windows, a browser or your CA's portal). Some files have an empty password - try leaving the field blank.
Why don't you show my private key?
A private key is the secret half of the certificate. Anyone who sees it can impersonate you, so the viewer only tells you that a key is present and what type and size it is.
Can it check if a certificate is revoked?
Not yet. Revocation (OCSP/CRL) needs to contact the certificate authority, which we keep for the server-side version of this tool.
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