CSR Decoder
Paste a PEM Certificate Signing Request to inspect its subject, public key, signature and SANs — entirely in your browser
About this tool
Decode a PEM Certificate Signing Request (PKCS#10) in your browser — inspect its subject, public key, signature algorithm and subject alternative names. CSR Decoder runs in the browser on DevTools. There is no signup, and your input stays on this device unless the tool explicitly performs a live network lookup.
What this tool does not do
- CSR Decoder is a free in-browser utility, not a hosted API. It does not keep server-side history and is not a substitute for production verification in your own stack.
How do I use this tool?
How do I use CSR Decoder?
Open CSR Decoder, enter or paste your input, and copy the result. The page works without an account.
Related guides
Why Your TLS Certificate Chain Breaks (and How to Fix It)
A field guide to 'unable to get local issuer certificate' and friends. What a certificate chain is, why order and intermediates matter, and how to find the broken link in a PEM bundle.
Reading a PEM Certificate: Subject, Issuer, SANs and Expiry
What the fields in a PEM certificate mean, why Subject Alternative Names matter more than the Common Name, and how to decode expiry and key usage.
How to Decode a CSR Before Sending It to a Certificate Authority
Inspect a Certificate Signing Request before you send it off. Learn what the Subject, SAN, public key and signature mean, and why modern browsers ignore CN in favor of the Subject Alternative Name.
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