CSR Decoder
Decode a Certificate Signing Request locally, inspect SANs and key details, and check whether the requested hosts are actually covered before you submit it.
CSR Decoder – Free Online Tool
Decode Certificate Signing Requests locally with subject and SAN parsing, key algorithm details, host coverage checks, readiness warnings, and OpenSSL-style summaries.
Free CSR Decoder for SSL Certificate Requests
The ToolsMint CSR Decoder reads a Certificate Signing Request and shows the subject, Subject Alternative Names, key algorithm, key size, signature algorithm, and SHA-256 fingerprints. It is useful when reviewing a CSR before sending it to a certificate authority or troubleshooting a request from a server, teammate, hosting panel, or client.
Decode PEM or DER CSR Files Without Uploading
Certificate requests often contain internal hostnames, staging names, customer domains, and organization details. ToolsMint decodes the CSR locally in your browser so the request is not uploaded to a backend service. Paste PEM text or upload a .csr, .pem, or DER request and inspect it privately.
Check SAN Coverage and Wildcard Behavior
A CSR can look correct at a glance while still missing the exact host you need. The built-in coverage checker tests whether a host is covered by the Common Name or SAN list and explains wildcard behavior such as why *.example.com covers api.example.com but not example.com or deep subdomains.
CSR Readiness Assistant for Common Mistakes
Modern certificate authorities rely on SAN entries, and browser trust rules make hostname details important. The readiness assistant flags missing SANs, Common Name mismatches, internal-only names, suspicious wildcard formats, and other issues that can cause rework before the CSR is submitted.
OpenSSL-Style Subject Summary and Fingerprints
The decoder also builds a copy-ready OpenSSL-style subject string and shows request and public-key SHA-256 fingerprints. That makes it easier to document the request, compare it with a generated private key or issued certificate, and hand off clear details to ops or security teams.
Frequently Asked Questions
Everything you need to know about the CSR Decoder.
Is this CSR decoder free?
Yes. It is free with no signup, no watermark, and no account requirement.
Does my CSR leave my browser?
No. The CSR is decoded locally in your browser. ToolsMint does not upload or store the request.
Can it decode both PEM and DER CSR files?
Yes. You can paste PEM text or upload a PEM or DER CSR file. The decoder normalizes the request before parsing it.
Does the decoder verify the private key?
No. A CSR does not contain the private key. The tool decodes the public request details and fingerprints, but it cannot prove private-key possession beyond what is already represented in the CSR signature.
What does the coverage checker do?
It tests whether a hostname is covered by the Common Name or SAN entries in the CSR and explains wildcard matches and mismatches in plain language.
Why does the tool warn about missing SANs?
Modern browsers and certificate authorities expect domains to be listed in the Subject Alternative Name extension. A Common Name by itself is usually not enough for a production website certificate.