Base64 Certificate Decoder
Got a base64 blob and not sure what is inside? Paste it. We auto-detect PEM, bare base64, or hex; report what each block looks like (X.509 cert, CSR, generic ASN.1); show the DER bytes; and emit a clean PEM.
Input
Result
What this tool does
Many tools spit out raw base64 with no header. This tool figures out what is inside the bytes (X.509 cert? CSR? something else?), normalises to DER, and re-armours into PEM with the right label. If you have a chain of multiple PEM blocks, all of them are reported.
Reach
PEM, bare base64 (PKCS#7-style), and hex are all accepted.
Decoding a base64 / PEM certificate
Certificates are shipped as base64 text far more often than as raw binary — a PEM file is just DER wrapped in base64 with -----BEGIN CERTIFICATE----- markers. This tool takes that base64 (with or without the PEM header) and decodes the certificate so you can read its fields without saving a file or running OpenSSL.
Typical use: you copied a certificate out of a config file, a Kubernetes secret, or a log line and want to know what it is. Paste it here to see the subject, issuer, validity window and key details. It is read-only inspection — it does not build a chain or check revocation, so pair it with the certificate-chain and X.509 viewer tools for the full picture.
Frequently asked questions
Do I need the BEGIN/END lines?
No — the decoder accepts raw base64 or a full PEM block. It strips the armour automatically.
Can it read a binary (DER) certificate?
For binary DER, use the PEM ↔ DER tool to convert first, or the X.509 viewer which handles both. This tool focuses on base64/PEM input.
Is the certificate uploaded anywhere?
No. Decoding happens locally; public certificates are not secret, but nothing leaves your browser regardless.
What is the difference between a certificate and a private key block?
The PEM header names it: CERTIFICATE holds the public certificate and is safe to share, while PRIVATE KEY blocks hold secret material. Check the header before pasting anything anywhere.
Can a file contain more than one certificate?
Yes — bundles and chain files routinely concatenate several PEM blocks, which is why this tool handles multi-block input rather than assuming one certificate per paste.