Everything runs on your machine — your input is processed right here in your browser and never uploaded to any server.
Paste one or more PEM certificates ("BEGIN CERTIFICATE" blocks).
Click "Convert to DER".
One certificate downloads as a .der file named after its subject; several download together as a ZIP.
PEM and DER are the same certificate in two coats: PEM is the Base64 text form with BEGIN/END armor, DER the raw binary encoding. Java keytools, some appliances, and older Windows components ask specifically for .der or binary .cer — this converter strips the armor and hands you exactly that.
Paste one certificate for a single .der download, or a whole chain to get each certificate converted and zipped together, named by its subject. Every certificate is parsed before converting, so a stray or truncated block is caught instead of producing a corrupt file.
100% private“The conversion is a local re-encoding — your certificates are parsed and rewritten entirely in your browser and never uploaded. Certificates are public data, and no private key is involved.”
Encoding only. DER is the binary ASN.1 form; PEM wraps that same binary in Base64 between BEGIN/END lines so it can travel through text systems. Converting between them never changes the certificate itself.
A .cer file can be either encoding — Windows uses the extension for both. The file this tool produces is binary DER; rename it to .cer if a tool insists on that extension.
No — this page deliberately handles certificates only. Keeping keys out of tools that do not need them is good hygiene; key format conversions are best done with openssl on your own machine.