Quick take
Paste a PEM certificate and read the subject, issuer, dates, and SANs.
- Paste a leaf certificate PEM and review subject, issuer, validity, SAN, and fingerprints.
- Load a self-signed certificate to inspect its basic constraints and key usage.
SSL Certificate Decoder
Decoded certificate details will appear here. Parsing happens locally in your browser.
Where it fits
Use SSL Certificate Decoder for inspecting PEM certificates during TLS setup, renewal checks, mismatch debugging, and certificate inventory review. It works well when you want subject, issuer, SAN, validity dates, fingerprints, public key details, and extension notes and do not need a bigger workflow around it.
- Best fit: inspecting PEM certificates during TLS setup, renewal checks, mismatch debugging, and certificate inventory review.
- You start with a public PEM certificate or certificate file.
- The useful choices are which certificate block to inspect and whether the result should be compared with CSR or deployment records.
- Check expiration date, SAN coverage, issuer, fingerprint, key size, and certificate purpose.
- You end up with subject, issuer, SAN, validity dates, fingerprints, public key details, and extension notes.
What the output does and does not prove
- The PEM block is decoded and parsed as X.509 data in your browser.
- The tool extracts subject, issuer, validity dates, public key information, common extensions, and SHA-1 / SHA-256 fingerprints.
- It does not connect to a remote website or fetch a live TLS certificate.
A clean way to use SSL Certificate Decoder
- Start with a public PEM certificate or certificate file.
- Choose which certificate block to inspect and whether the result should be compared with CSR or deployment records.
- Run the tool once, then review expiration date, SAN coverage, issuer, fingerprint, key size, and certificate purpose.
- Copy, export, or download subject, issuer, SAN, validity dates, fingerprints, public key details, and extension notes.
- Treat the output as one checkpoint, then verify the next step in the real workflow.
What to watch for
- Certificate decoding reads public certificate material; it does not connect to a live host or test the TLS handshake.
- A valid certificate parse does not prove that the server is configured correctly.
- Check SAN entries instead of relying only on the Common Name.
- Never paste private keys into certificate decoder workflows.
How your data is handled
Certificate text and local files are processed in your browser. Toolumina does not upload, save, or log the certificate content.
FAQ
Does this connect to my website?
No. This version only decodes certificate text or local files that you provide.
Why does it only show the first certificate?
This tool focuses on one certificate at a time. If a chain is pasted, it detects multiple blocks and parses the first one.
Can I paste a private key?
No. Private keys are rejected because this tool is for public certificate material only.
Does a valid certificate mean the site is fully safe?
No. Certificate parsing only explains the certificate fields; it is not a full TLS or website security audit.