Runs in your browser
Paste a certificate signing request to read every field your certificate authority will see (subject, requested hostnames, key type and size, signature algorithm) and to confirm its signature matches its public key. The decoding happens on this page, and nothing you paste is sent anywhere.
Decoded in this browser tab. Nothing you paste or load is uploaded, stored or logged.
Paste a request that starts with -----BEGIN CERTIFICATE REQUEST----- to see its subject, names, key and signature check.
A CSR is a short signed message: the names you want on the certificate, your public key, and a signature made with the matching private key.
| Field | What to check |
|---|---|
| Common name (CN) | The main hostname, such as www.example.com. Browsers do not match against it, so it must also appear in the SAN list. |
| Subject alternative names | Every hostname, wildcard or IP address the certificate should cover. This is the list browsers actually match. |
| Organisation, locality, state | Only used for organisation-validated (OV) and extended-validation (EV) certificates. A domain-validated certificate leaves them out, whatever the CSR says. |
| Country (C) | A two-letter ISO 3166 code such as GB or US. A full country name is a common reason for a rejected request. |
| Organisational unit (OU) | Public certificate authorities stopped putting it in TLS certificates in September 2022, so it is dropped if present. |
| Public key | RSA of at least 2048 bits, or ECDSA on P-256 or P-384. The matching private key stays on your server and is never part of the CSR. |
| Signature algorithm | The hash used to sign the request, normally SHA-256. The certificate authority chooses its own algorithm for the certificate it issues. |
| Signature | Proof that whoever made the request holds the private key. If it does not match the public key, the request was changed after it was signed. |
| Challenge password | An optional attribute from older enrolment systems. It sits in the CSR as plain text, so anyone with the file can read it. |
The same checks from a terminal. Each command below was run against the sample CSR on this page, and the output is what OpenSSL 3 printed.
openssl req -in request.csr -noout -verifyCertificate request self-signature verify OKopenssl req -in request.csr -noout -subjectsubject=C = GB, ST = Isle of Man, L = Douglas, O = Beacon Test Ltd, CN = www.example.com, emailAddress = ops@example.comopenssl req -in request.csr -noout -text | grep -A1 'Subject Alternative Name'X509v3 Subject Alternative Name:
DNS:www.example.com, DNS:example.com, DNS:*.api.example.com, IP Address:192.0.2.10, email:ops@example.com, URI:https://example.com/Compare a SHA-256 hash of the public key in the CSR with one derived from your private key. The decoder already shows the first value as Public key SHA-256, so on the server you only need the second command.
openssl req -in request.csr -noout -pubkey \
| openssl pkey -pubin -outform der | openssl dgst -sha256SHA2-256(stdin)= 199f5b2364f768995f0f743f175a29f06d6596a653aa1b15ad0caa9646a9d5c6openssl pkey -in private.key -pubout -outform der | openssl dgst -sha256SHA2-256(stdin)= 199f5b2364f768995f0f743f175a29f06d6596a653aa1b15ad0caa9646a9d5c6Identical hashes mean the CSR was made from this key. The certificate decoder shows the same value for an issued certificate, so you can trace a certificate back to its CSR and key.
Each warning is something a certificate authority is likely to reject, or a field that will not end up on the certificate.
Decoding the request is the cheapest point to catch a mistake. After that, the job is making sure the issued certificate reaches the server and is renewed in time.
For example: openssl req -new -newkey rsa:2048 -nodes -keyout example.key -out example.csr -subj "/CN=example.com" -addext "subjectAltName=DNS:example.com,DNS:www.example.com". The private key never leaves that machine.
Check the names, the key size and the signature now. A rejected request costs a round trip with the certificate authority.
Paste it into the certificate decoder and confirm it covers the same names and shows the same public key SHA-256 as your CSR.
Run the SSL certificate checker against the hostname once the certificate is installed, then save it as a monitor so you hear about expiry before your visitors do.
A CSR holds only public information: the names, the public key and a signature. On this page it is not sent anywhere either, because the decoding and the signature check run in your browser. Never paste a private key, here or anywhere else; the decoder refuses to read one.
The CSR was signed with the private key that matches the public key inside it. The decoder checks this with your browser's Web Crypto API. A mismatch means the request was changed after it was signed, and a certificate authority will reject it. A few algorithms, such as DSA or SHA-224, cannot be checked in a browser, and the decoder says so instead of guessing.
No. It carries only the public half. If the text you have includes a line such as BEGIN PRIVATE KEY, that part is your private key and should stay on the server.
OpenSSL only adds them when asked, with -addext "subjectAltName=DNS:example.com,DNS:www.example.com" on OpenSSL 1.1.1 or later, or a subjectAltName line in the request config. Most certificate authorities copy the common name in for you, but listing every hostname yourself avoids a certificate that misses one.
Yes, a certificate pasted here is decoded too. The certificate decoder is built for them, though: it reads whole chains, checks each signature against its issuer, and counts the days left.