PEM Decoder
Inspect PEM structure and Base64 body locally.
PEM Decoder inspects a pasted PEM-formatted certificate, CSR, or key block entirely in your browser. It reports the block type, Base64 body length, decoded byte count, and a short hex preview—without performing full X.509 validation or ever uploading the content.
How it works
The tool matches the pasted text against the standard "-----BEGIN TYPE-----"/"-----END TYPE-----" PEM markers, confirms both labels match, strips whitespace from the Base64 body, and decodes it to bytes locally. It then reports the type, Base64 length, decoded byte length, and the first bytes as hex.
Benefits
- Quick structural sanity check for PEM blocks
- Works for certificates, CSRs, and key files (structure only)
- Hex preview confirms the Base64 body decodes to binary data
- Runs entirely client-side—no upload to any certificate authority or server
Use cases
- Verify a certificate file has correct BEGIN/END markers before submitting it
- Check that a CSR's Base64 body is not truncated
- Teach the structure of PEM-encoded cryptographic material
- Quickly measure the size of a certificate or key blob
Best practices
- Use a dedicated tool like OpenSSL for full X.509 field parsing and validation
- Never paste real private keys into any online tool, including this one
- Confirm BEGIN and END type labels match exactly before trusting a file
- Treat PEM structural checks as a first pass, not a security guarantee
Common mistakes
- Assuming this tool verifies certificate validity, expiry, or trust chains
- Pasting a partial PEM block missing the END marker
- Confusing a CSR (CERTIFICATE REQUEST) with an issued CERTIFICATE
- Treating the hex preview as a full decoded certificate—it only shows the first bytes
Privacy
Decoding happens entirely client-side using Base64 decoding built into the browser—no network request is made. Because PEM content can include private keys, this tool is marked sensitive and history requires explicit opt-in.
Frequently asked questions
- Does PEM Decoder validate the certificate chain or expiry?
- No. This tool only checks that BEGIN/END markers match and decodes the Base64 body to report its length and a short hex preview. It does not parse X.509 fields like validity dates, subject, or issuer, and does not perform full certificate validation.
- What PEM types are recognized?
- The tool recognizes common types such as CERTIFICATE, CERTIFICATE REQUEST, PRIVATE KEY, RSA PRIVATE KEY, EC PRIVATE KEY, PUBLIC KEY, and X509 CRL, but will still decode and report the Base64 body length for any BEGIN/END type it finds.
- Is it safe to paste a private key here?
- Avoid pasting real private keys into any online tool, including this one. Processing happens locally in your browser, but this tool is marked sensitive and treats any PEM content as potentially confidential.
- What does the hex preview show?
- It shows the first bytes of the decoded (Base64-decoded) content as hexadecimal pairs, giving you a quick sanity check that the content decodes to binary DER data without fully parsing the ASN.1 structure.
- Why did I get a 'BEGIN/END markers do not match' error?
- PEM blocks must open and close with the same type label, for example "-----BEGIN CERTIFICATE-----" paired with "-----END CERTIFICATE-----". A mismatch usually means the content was truncated or concatenated incorrectly.
- Can this tool decode multiple PEM blocks at once?
- It decodes the first well-formed PEM block it finds in the pasted text. For multiple blocks (like a certificate chain), decode them one at a time by pasting each block separately.
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