SSL Certificate Decoder

Inspect X.509 PEM certificates, check expiration countdowns, SAN domains, and cryptographic SHA-256 fingerprints with zero server logs.

Paste X.509 Certificate (PEM Format)

Presets:

Understanding X.509 TLS/SSL Public Key Certificates

Transport Layer Security (TLS) and Secure Sockets Layer (SSL) certificates authenticate the identity of websites and encrypt data in transit between web browsers and servers. Decoding certificates allows network engineers, DevOps specialists, and security auditors to verify certificate authority chains and prevent unexpected certificate expiration outages.

Key Inspector Capabilities

✓

Client-Side Zero-Log Decoding

Your private keys or public certificates never leave your browser. All ASN.1 and cryptographic fingerprinting occurs in local memory.

✓

Expiration Countdown

Instantly identify remaining validity days, exact expiration timestamps, and whether a certificate is active or expired.

✓

SAN & Domain Coverage

Extracts all Subject Alternative Names (SANs) to verify wildcard domains and multi-domain coverage.

✓

Cryptographic Fingerprint

Calculates SHA-256 checksums and identifies public key strength (RSA 2048, RSA 4096, ECC P-256).

✓

OpenSSL CLI Helper

Includes cheatsheets with copyable openssl commands for diagnosing production servers and converting cert formats.

✓

JSON Export

Export the parsed certificate metadata directly to JSON for automated CI/CD pipelines or audit reports.

Practical Security Scenarios

✓
DevOps & SRE Certificate Verification
Verify freshly provisioned Let's Encrypt, Cloudflare, or AWS ACM certificates before binding them to Nginx or Kubernetes ingress.
✓
SSL Expiration Monitoring
Confirm certificate renewal dates to prevent catastrophic production outages caused by expired HTTPS certificates.
✓
Security Auditing & CA Validation
Inspect intermediate and root CA chains to ensure internal compliance with PKI security standards.
✓
Wildcard & Multi-Domain Inspection
Check whether a given certificate covers specific subdomains through the Subject Alternative Names list.

Frequently Asked Questions

Is it safe to paste certificates into this online decoder?

Yes! This tool parses certificates 100% locally in your browser using the Web Cryptography API and client-side string parsers. No certificate data is ever transmitted to or logged on any external server.

Can this tool read private keys?

No. This tool is strictly designed for public X.509 certificates (marked by -----BEGIN CERTIFICATE-----). You should never paste private keys (BEGIN RSA PRIVATE KEY) into any online application.

What causes an 'Invalid certificate format' error?

X.509 certificates must be in PEM base64 format starting with '-----BEGIN CERTIFICATE-----' and ending with '-----END CERTIFICATE-----'. If you have a binary DER or PKCS#12 (.pfx/.p12) file, convert it to PEM first using OpenSSL.