Online Tool Store
SSL Certificate Decoder
Paste a PEM-encoded X.509 certificate to decode its subject, issuer, validity dates, serial number, and signature algorithm. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Paste a PEM-encoded X.509 certificate (starts with -----BEGIN CERTIFICATE-----). A freshly generated sample self-signed certificate is loaded below to try it out. Parsing happens entirely in your browser - nothing is uploaded.
How the SSL certificate decoder works
- A sample self-signed certificate loads and decodes automatically to demonstrate the tool.
- Paste your own PEM-encoded certificate to replace it.
- Review the decoded subject, issuer, validity dates, serial number, and signature algorithm.
FAQ
What certificate fields does this decode?
Subject, issuer, validity period (valid from/until), serial number, and signature algorithm - the core fields of an X.509 certificate.
Where do I get a PEM certificate to paste?
Export it from your server's certificate file, download it from your browser's site information panel, or copy it from wherever your certificate authority provided it - it should start with -----BEGIN CERTIFICATE-----.
Is my certificate uploaded anywhere?
No - the entire ASN.1/DER parsing happens locally in your browser using hand-written parsing logic. Nothing is sent to a server.
What is the sample certificate that loads automatically?
A freshly generated, real self-signed demo certificate created in your browser using the Web Crypto API, so you can see the decoder working immediately without pasting your own certificate first.
How we compare
| Feature | Online Tool Store | openssl x509 -text CLI | Browser certificate viewer |
|---|---|---|---|
| No install required | ✓ | ✗ | ✓ |
| Works with any pasted certificate | ✓ | ✓ | ✗ |
| Nothing uploaded to a server | ✓ | ✓ | ✓ |
Useful for quickly inspecting certificate details without installing OpenSSL or digging through browser dev tools.