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X.509 Decoder

Parse PEM/DER certificates and inspect subject, SAN, and validity locally.

Crypto & Certs
Privacy: 100% Client-Side. Your data never leaves this browser tab. Processing uses Web APIs and client-side libraries only.

What is X.509 Decoder?

X.509 Decoder is part of the stbox.dev developer sandbox. Parse PEM/DER certificates and inspect subject, SAN, and validity locally.

It sits in the Crypto & Certs category and is designed for day-to-day debugging, demos, and learning — without forcing you to paste secrets into opaque third-party SaaS forms whenever client-side execution is enough.

How to use this tool

  1. Open X.509 Decoder at https://stbox.dev/x509-decoder and review the privacy badge for runtime expectations.
  2. Paste or configure your input in the tool interface (tokens, URLs, files, or text depending on the utility).
  3. Copy results locally, or chain them into related stbox tools such as JWT, OAuth, or the REST client.

Frequently asked questions

Is my data sent to a server?

X.509 Decoder runs 100% in your browser. Inputs stay on your device and are not logged or stored by stbox servers.

Is stbox free to use?

Yes. Tools are provided as-is for testing and debugging with no account required for core utilities.

Can I use this for production secrets?

Prefer dedicated KMS/HSM workflows for production key material. stbox is optimized for local debugging and education.