What Is a CSR (Certificate Signing Request)?
Understand what a CSR is, what's inside it, how it relates to your private key, and how to decode and check one before you order an SSL certificate.
By the ToolsHub team · Updated August 20, 2026
A CSR (Certificate Signing Request) is a small, encoded block of text you generate on your server when you want an SSL/TLS certificate. You send it to a Certificate Authority (CA), which uses it to issue the certificate that makes your site load over HTTPS.
What's inside a CSR
A CSR bundles the details the CA needs to identify you, together with your public key:
- Common Name (CN) — the exact domain the certificate is for, e.g.
www.example.com. - Organisation, locality, country — who is requesting the certificate.
- Public key — half of a key pair; the matching private key stays on your server.
The whole request is signed by your private key, which proves you hold it — but the private key itself is never included and must be kept secret.
Why decode a CSR before you submit it
A single wrong character in the common name means the CA issues a certificate for the wrong name, and you have to start again. Before submitting, decode the CSR and check every field. Our CSR Decoder reads the request and shows the domain, organisation and key details in plain text — entirely in your browser, so nothing is uploaded.
CSR, certificate and key — how they fit together
The CSR produces a certificate, and that certificate must match the private key on your server. If they don't match, HTTPS fails. Use the Certificate Decoder to inspect an issued certificate's details and expiry, the Certificate Key Matcher to confirm the certificate, key and CSR belong together, and the SSL Checker to verify the certificate is installed and trusted once it's live.
Frequently asked questions
- What is a CSR used for?
- A CSR (Certificate Signing Request) is the block of text you send to a Certificate Authority to order an SSL/TLS certificate. It contains your domain and organisation details and your public key, all signed by your private key.
- What information is in a CSR?
- The common name (your domain), organisation, locality and country, plus your public key. It does not contain your private key. You can see all of it by decoding the CSR.
- How do I check a CSR before submitting it?
- Decode it and confirm the common name and details are exactly right — a typo means a reissued certificate. Our CSR Decoder shows the fields in plain text in your browser.
- Does a CSR contain my private key?
- No. A CSR carries your public key and is signed by the private key, but the private key itself never leaves your server. Keep the private key secret.