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Decode SSL certificates (subject/expiry/chain). Use for debugging certs. Input: PEM text ≤10MB. Returns parsed fields. 100% client-side.
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SSL certificate decoder that parses X.509 fields including subject, issuer, serial number, validity period, subject alternative names (SAN), key algorithm, and fingerprint. Displays an expiry countdown timer, chain analysis showing all intermediate and root certificates, an ASN.1 structure dump, and key usage/extended key usage details.
Debugging SSL/TLS issues requires inspecting raw certificate fields that are opaque in most UIs. This tool surfaces every detail — including chain order, SANs, and ASN.1 structure — so developers can quickly diagnose misconfigurations.
This tool is part of the DevStackIO platform — a collection of free online developer tools from DevStackIO. Browse more free developer resources on DevStackIO.
DevOps engineers, security analysts, penetration testers, and backend developers who manage TLS certificates or troubleshoot HTTPS connectivity.
Paste a PEM-encoded certificate (or several in chain order) into the input area.
Click Decode to parse the X.509 fields; the subject, issuer, serial, and validity are displayed at the top.
Review the Subject Alternative Names (SAN) list — both DNS names and IP addresses are shown.
Read the expiry counter showing days/hours/minutes until (or since) expiration in real time.
Click the Chain tab to view each certificate in the chain with its subject, issuer, and fingerprint.
Open the ASN.1 tab to see the raw ASN.1 structure dump for deep inspection.
Input: PEM block for a Let's Encrypt certificate → output shows subject CN=example.com, issuer CN=R3, valid 90 days, SANs [example.com, www.example.com], SHA-256 fingerprint, 45 days until expiryInput: Chain of 3 PEM blocks (leaf → intermediate → root) → chain analysis shows each level, validates trust path order, and flags any missing intermediatesWhat PEM formats are accepted?
Standard -----BEGIN CERTIFICATE----- blocks, including multiple concatenated blocks for chain analysis.
Can I decode a certificate from a remote server directly? Not yet
paste the PEM content obtained via openssl s_client or your browser.
What is the difference between SHA-1 and SHA-256 fingerprints?
SHA-256 is the modern, cryptographically stronger hash; SHA-1 is deprecated for security.
Does it support wildcard certificates? Yes
wildcard SANs like *.example.com are shown with the asterisk preserved.
Authoritative specifications, standards, and in-depth reading for SSL Certificate Decoder.
Client-side basic ASN.1 decoder with limited field support. For production certificate inspection, use OpenSSL or dedicated certificate tools.
Paste a PEM certificate, upload a .pem/.crt/.cer file, or click "Load Example" to get started
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Learn the concepts behind this tool.
HTTPS
HTTPS is HTTP over TLS, encrypting requests and responses to provide confidentiality, integrity, and authentication. Browsers show a lock icon when the TLS certificate is valid.
View in glossary →SSL
Secure Sockets Layer, now succeeded by TLS, encrypts network traffic and authenticates servers via certificates. The term SSL is still used colloquially to mean TLS encryption.
View in glossary →TLS
Transport Layer Security encrypts data in transit and authenticates the peer via certificates, succeeding SSL. It secures HTTPS, email, and other protocols end-to-end.
View in glossary →