About Certificate & CSR Decoder
This free certificate decoder shows what is inside an SSL/TLS certificate or a certificate signing request (CSR). Paste a PEM certificate, a whole chain or a CSR, or drop a .crt, .cer, .pem, .der or .csr file, and see the common name, the SAN domains, the issuer, the validity dates and days left, the key type and size, the signature algorithm, the key usage, the serial number and the SHA-256 and SHA-1 fingerprints.
For a CSR it also checks the request’s signature, so you know it was not damaged in transit. Decoding happens in your browser, so you can safely check internal certificates.
How to use Certificate & CSR Decoder
- 01
Paste a PEM certificate, a chain or a CSR, or drop a .crt, .cer, .der or .csr file.
- 02
Read the subject, SAN domains, issuer, validity dates and key details.
- 03
Copy the serial number or fingerprints if you need them.
When to use it
- Checking when a certificate expires.
- Confirming a CSR has the right domains before sending it.
- Checking which domains a certificate covers.
- Reading the issuer and order of a CA bundle.
- Copying a fingerprint or serial number for a configuration file.
Frequently asked questions
Can it read a whole certificate chain?
Yes. Paste the chain or CA bundle and every certificate is shown in order.
Does it check if the certificate is trusted?
It shows dates, issuer and whether it is self-signed, and verifies CSR signatures. It does not check revocation or a browser’s trust store.
Is it safe to paste a certificate here?
Yes. Certificates are public anyway, and decoding runs in your browser. Never paste a private key into any website you do not trust.