Generate an RSA keypair and export it as PEM.
The pair is generated by your browser with Web Crypto and exported as PEM. The private key is never transmitted, and 4096 bits can take a few seconds.
Every other converter asks you to upload first. Yours never leaves the tab.
After that it works with the network off.
Your file is processed on your own processor.
Close the tab and every trace is gone.
Need anything else? Ask on GitHub.
Every line is public and MIT licensed. Check it, fork it, or build the next tool.