Thanks for the pointer to NetRipper; tinyapps.org is the best!

Fiddler MITM's creating a self-signed cert for each domain, which fails on apps that do cert pinning. I didn't get far enough to try but it also sounded like it didn't support smart cards for client certs in this mode either, asking for the private key in a file.

Just turning on the 'open dev tools for new windows' setting in Chrome is often enough to get what I need easily.