Best Free Online Developer Tools to Use in 2026
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Aug 08, 2026
X.509 Certificate Viewer
Inspect X.509 certificate details — issuer, subject, validity, extensions, and fingerprints
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Enter a PEM certificate and click View Certificate
What Is an X.509 Certificate?
An X.509 certificate is a digital document that binds a public key to an identity (such as a domain name or organization). It is the foundation of TLS/SSL security on the web. Certificates contain essential information including the subject (who the certificate is issued to), issuer (who issued it, typically a Certificate Authority), validity period (not before and not after dates), serial number, signature algorithm, public key algorithm and size, and extensions like Subject Alternative Names (SANs), Key Usage, and Basic Constraints. This viewer parses PEM-encoded X.509 certificates and displays all fields in a readable format. It also computes SHA-256 and SHA-1 fingerprints. System administrators, security engineers, and developers use it to inspect certificate details, troubleshoot SSL issues, verify certificate chains, and check expiration dates.
How to Use This Tool
- Paste a PEM certificate — Enter or paste a PEM-encoded X.509 certificate into the input area.
- Click View Certificate — The tool parses the certificate's ASN.1 structure and extracts all fields.
- Review the details — The output displays subject, issuer, validity dates, serial number, signature algorithm, public key information, and extensions.
- Check fingerprints — SHA-256 and SHA-1 fingerprints are shown for certificate identification.
- Use examples — Click the example buttons (Server, CA, Self-Signed) to see sample certificates and their parsed data.
Frequently Asked Questions
Is my data sent to a server?
No. All processing is performed locally in your browser. Your certificate never leaves your device.
What certificate formats are supported?
The tool supports PEM-encoded X.509 certificates. DER-format certificates can be converted to PEM using an external tool first.
Can I view certificate extensions?
Yes. The tool displays key extensions including Subject Alternative Names (SANs), Key Usage, Extended Key Usage, Basic Constraints, and Authority Key Identifier.
What is a certificate fingerprint?
A fingerprint is a hash of the certificate's DER-encoded content. It uniquely identifies the certificate and is used for certificate pinning and verification.
Is this tool free to use?
Yes. This tool is completely free with no usage limits or registration required.
Last updated: 17 Aug 2026
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