Crypto
Certificate Decoder
Decode PEM and CRT certificate structure locally.
About Certificate Decoder
Certificate Decoder reads PEM or CRT content and summarizes certificate fields so you can inspect issuers, subjects, dates, and encoded structure.
Common uses
- Check certificate validity dates before replacing a cert.
- Inspect subject and issuer names in a copied PEM block.
- Confirm that a file contains certificate data rather than another PEM type.
Good to know
This decoder explains certificate content. It does not perform a full chain validation or confirm that a certificate is trusted by a device.
How to read certificate fields
Review the subject, issuer, serial number, validity dates, subject alternative names, and key usage fields. These details help explain why a certificate is accepted or rejected by a client.
Validation limits
Decoding a certificate is not the same as building a trusted chain. A certificate can parse correctly while still being expired, untrusted, issued for another host, or missing intermediate certificates.
Common mistakes
Make sure the pasted block is a certificate and not a private key, certificate request, or unrelated PEM value. The header line usually tells you what kind of data you have.
Before you rely on the output
- Treat generated cryptographic values as development aids unless your production security process has approved the browser, algorithm, and key-handling workflow.
- Privacy mode: inputs are processed locally in your browser and are not intentionally sent to an application server.