Certificate to CSR Command Generator
Paste an existing certificate and get a ready-to-run openssl command that creates a
matching CSR — reusing its subject and SANs. The certificate is read entirely in your browser.
New to this? Read the Certificate to CSR guide →
.key and a matching .csr.
Needs OpenSSL 1.1.1 or newer (for -addext). Run it in a terminal where you want the new key and CSR saved.
Paste a certificate and press Generate command.
How to use this tool
- Paste an existing PEM certificate.
- The tool reads its subject and Subject Alternative Names and builds the OpenSSL command to generate a matching CSR.
- Run that command on your server, where your private key lives, to produce the new CSR.
Everything happens in your browser; the certificate is only read locally to extract its details.
What a CSR is
A Certificate Signing Request is the file you send to a certificate authority to ask for a certificate. It contains your public key and the subject details (the domain names, organisation and so on) and is signed by your private key. The CA uses it to issue the certificate.
When you'd use it
The usual case is renewing or reissuing a certificate when you no longer have the original CSR. Rather than retyping every domain and field by hand, you copy them straight from the certificate you already have. One important note: a certificate does not contain your private key, so this tool cannot and does not produce one. The generated command runs against your existing key on the server, which is exactly where the private key should stay. To inspect what is inside a certificate first, use the certificate decoder.
Where you'd use this
Renewing a certificate for an existing service when the original CSR is long gone, and you need one with exactly the same subject and SANs.
For example: A load balancer certificate expires in a week and covers six subdomains. Generating a CSR from the current certificate reproduces all six SANs exactly, rather than someone retyping them and missing one.
Frequently asked questions
What is a CSR?
A Certificate Signing Request (CSR) is the file you send to a certificate authority to request a certificate. It contains your public key and subject details like the domain name and organisation.
Why generate a CSR from an existing certificate?
When renewing or reissuing, it is convenient to reuse the exact subject details from your current certificate so the new one matches. This tool helps you carry those details across.
Is my certificate or key uploaded?
No. Everything is processed in your browser; private key material never leaves your machine.