Open CRT Files Online
A .crt or .cer file holds an X.509 certificate, either as PEM text or binary DER. Web servers use them to prove their identity over HTTPS.
X.509 certificate · .crt, .cer, .der
What you see in the CRT viewer
- Validity status with an expiry countdown
- All extensions in plain English
- Signature check against the issuer
- Fingerprints to copy
Other ways to open CRT files
Windows
Double-click opens the certificate dialog.
macOS
Keychain Access or Quick Look.
Phone & tablet
Only installation is offered; view it here instead.
Frequently asked questions
Is my CRT file uploaded?
No. The file is read by your browser and shown on your own device. Nothing is sent to a server, and it is gone when you close the tab.
How do I open a CRT file without installing software?
Drop the .crt, .cer, .der file on this page. It opens straight away in the SSL Certificate Viewer, on Windows, macOS, Linux, Android and iPhone alike.
What if my CRT file doesn't open?
The viewer checks the file's content, not just its name. If it is damaged or not really a CRT file, you'll see an error or can switch to the hex view to look at the raw bytes.