What this tool does
Decode PEM SSL certificates locally, inspect subject, issuer, SAN, dates, fingerprints, and key details in your browser.
- 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.
- Paste a certificate chain and parse the first certificate while noting that multiple blocks were detected.
SSL Certificate Decoder
Decoded certificate details will appear here. Parsing happens locally in your browser.
When this tool is a good fit
SSL Certificate Decoder helps when you need subject, issuer, SAN, validity dates, fingerprints, public key details, and extension notes from a public PEM certificate or certificate file. It is most useful for inspecting PEM certificates during TLS setup, renewal checks, mismatch debugging, and certificate inventory review. The notes below focus on the settings that matter, the checks worth doing before you export, and the limits that tend to cause mistakes.
- Takes a public PEM certificate or certificate file.
- Lets you adjust which certificate block to inspect and whether the result should be compared with CSR or deployment records.
- Calls out what to review: expiration date, SAN coverage, issuer, fingerprint, key size, and certificate purpose.
- Produces subject, issuer, SAN, validity dates, fingerprints, public key details, and extension notes.
- Fits common jobs such as inspecting PEM certificates during TLS setup, renewal checks, mismatch debugging, and certificate inventory review.
Example jobs
- 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.
- Paste a certificate chain and parse the first certificate while noting that multiple blocks were detected.
How to use SSL Certificate Decoder
- Prepare a public PEM certificate or certificate file.
- Set which certificate block to inspect and whether the result should be compared with CSR or deployment records before running the tool.
- Generate or process the result, 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.
- Run a second pass if the destination system, document, or workflow has stricter requirements.
What to know before you use it
- 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.
- 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.
Checks and edge cases
- 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.