How do I check that a private key matches a certificate?

Paste the key and the certificate together. The tool takes the public key out of the private key structure (or has the browser derive it), computes its SHA-256 pin and compares it with every certificate and CSR in the input; a match is labeled “Matches the public key of certificate #1”. It all happens locally — the private key is never displayed or uploaded. Clear the box when you’re done.

What order should a certificate chain be in?

A server chain is normally ordered leaf certificate → intermediate certificate(s); the root usually isn’t included. The tool finds each certificate’s issuer by name (and AKI / SKI), verifies the signature with the issuer’s key and warns when the pasted order doesn’t follow the issuing relationship. “Issuer not in the list” means the parent is missing — the CA Issuers URL tells you where to download it.

Which formats are supported?

PEM text (BEGIN CERTIFICATE, CERTIFICATE REQUEST, PRIVATE KEY, RSA PRIVATE KEY, EC PRIVATE KEY, PUBLIC KEY, PKCS7 and more, mixed in one paste), bare Base64, hex DER, binary .der / .cer / .crt files and .p7b bundles. For password-protected keys only the encryption scheme is shown (PBES2, PBKDF2 iterations, cipher) — nothing is decrypted. OpenSSH-format keys must be converted first.

What are SCTs and OCSP Must-Staple?

An SCT (Signed Certificate Timestamp) proves the certificate was submitted to a Certificate Transparency log; Chrome and Safari require them on publicly trusted certificates, and the tool lists each SCT’s log ID and time. OCSP Must-Staple (the TLS Feature extension) tells browsers to expect a stapled OCSP response during the handshake, so make sure OCSP stapling is enabled on the server before using it.

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🛂SSL Certificate Decoder - X.509, PEM, CSR and Chain Checker

When you deploy HTTPS you often need to know which names a certificate covers, when it expires, whether the intermediate is the right one and whether the private key matches. Paste PEM (a whole chain at once is fine) or drop a .crt, .cer, .der, .pem, .csr, .key or .p7b file, and a built-in ASN.1 DER parser decodes it field by field: subject and issuer DNs, serial number, validity with days remaining, signature algorithm, public key type and size (RSA bits and exponent, EC curve, Ed25519), Subject Alternative Names, key usage and extended key usage, basic constraints, SKI/AKI, OCSP and CA Issuers URLs, CRL distribution points, certificate policies (DV/OV/EV), Certificate Transparency SCTs and OCSP Must-Staple, plus SHA-1/SHA-256 fingerprints and the public key pin. Multiple certificates are linked into a chain by issuer and subject, and each signature is verified with the issuer’s public key through your browser’s WebCrypto. CSRs (PKCS#10), PKCS#1/PKCS#8/SEC1 private keys, SPKI public keys and PKCS#7 bundles are supported too; for private keys you only see the type and size and which certificate they match — never secret values. A raw ASN.1 tree shows every field’s offset and encoding. Everything runs locally in your browser.

Free · No sign-up · Runs in your browserLast updated: 2026-10-26

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How to use SSL Certificate Decoder

1Paste PEM, Base64 or hex, or open or drop a certificate file
2Read each certificate’s details, the chain links and the signature checks
3Switch to the ASN.1 tree or the PEM / DER tab to copy PEM or download DER

FAQ

How do I check that a private key matches a certificate?: Paste the key and the certificate together. The tool takes the public key out of the private key structure (or has the browser derive it), computes its SHA-256 pin and compares it with every certificate and CSR in the input; a match is labeled “Matches the public key of certificate #1”. It all happens locally — the private key is never displayed or uploaded. Clear the box when you’re done.
What order should a certificate chain be in?: A server chain is normally ordered leaf certificate → intermediate certificate(s); the root usually isn’t included. The tool finds each certificate’s issuer by name (and AKI / SKI), verifies the signature with the issuer’s key and warns when the pasted order doesn’t follow the issuing relationship. “Issuer not in the list” means the parent is missing — the CA Issuers URL tells you where to download it.
Which formats are supported?: PEM text (BEGIN CERTIFICATE, CERTIFICATE REQUEST, PRIVATE KEY, RSA PRIVATE KEY, EC PRIVATE KEY, PUBLIC KEY, PKCS7 and more, mixed in one paste), bare Base64, hex DER, binary .der / .cer / .crt files and .p7b bundles. For password-protected keys only the encryption scheme is shown (PBES2, PBKDF2 iterations, cipher) — nothing is decrypted. OpenSSH-format keys must be converted first.
What are SCTs and OCSP Must-Staple?: An SCT (Signed Certificate Timestamp) proves the certificate was submitted to a Certificate Transparency log; Chrome and Safari require them on publicly trusted certificates, and the tool lists each SCT’s log ID and time. OCSP Must-Staple (the TLS Feature extension) tells browsers to expect a stapled OCSP response during the handshake, so make sure OCSP stapling is enabled on the server before using it.