X.509 Certificate (SSL/TLS) Parser
The X.509 Certificate Parser reads any SSL/TLS certificate in PEM format (starting with -----BEGIN CERTIFICATE-----) and displays its details clearly: Subject and Issuer, the validity window (with a warning if it's expired), serial number, signature and public-key algorithms, Subject Alternative Names (SAN), and a SHA-256 fingerprint. A common task for sysadmins and developers checking a certificate before deploying it. This tool doesn't verify the signature or chain of trust — it only shows the certificate's structure. All parsing happens in your browser; the certificate is never uploaded to a server — important since a certificate can reveal internal hostnames.
The certificate is parsed entirely in your browser; it is never sent to any server.
This tool only shows the certificate's structure — it does not verify the signature or the chain of trust. Don't rely on it to confirm a certificate is trusted or genuinely issued by the claimed authority.
Or drop a certificate file here
.pem, .crt, or .cer files
What this tool does
Reads an X.509 certificate and displays its details: issuer, subject, validity period, signature and public-key algorithms, subject alternative names and fingerprint.
When to use it
- Checking a site certificate's expiry before it actually expires.
- Examining a certificate you received to see who issued it and which domains it covers.
- Debugging a secure connection problem whose cause is unclear.
- Confirming a certificate covers a particular subdomain via its alternative names.
How to use it
- Paste the certificate text into the field, or put the certificate file on the drop area.
- Read the fields shown, noting the validity status: valid, expired or not yet valid.
A practical example
Input
A site certificate in text form.
Output
The issuer and subject, the start and end dates with a validity status, the domains it covers, and the certificate's fingerprint.
Limitations
- This reads the certificate; it does not verify its trust chain and does not contact anyone to check whether it has been revoked.
- A certificate can be structurally sound and still be expired or issued by an untrusted authority — reading it is not accepting it.
- A malformed or invalid certificate is rejected with a clear message.
Privacy and processing
The certificate is parsed entirely in your browser and is never sent to any server.
Technical notes
- Parsing reads the certificate's binary structure directly, and the fingerprint is computed locally from its contents.
Frequently Asked Questions
No — the certificate is parsed entirely in your browser via JavaScript, and is never sent to any server — important since a certificate can reveal internal domain or server names.