HTTP Mock is the latest tool in HTTP Toolkit, a suite of beautiful & open-source tools for debugging, testing and building with HTTP(S), on Windows, Linux & Mac.

This does look useful.

Interesting implementation note: https://news.ycombinator.com/item?id=21072087

The trick is that it starts the application to be intercepted for you, so it can control it a little. It then does some magic to get that specific instance of the application to trust the certificate. There’s a lot going on there, but as an example: Chrome has a --ignore-certificate-errors-spki-list to inject the hashes of extra CAs that can be trusted in this specific Chrome instance. When HTTP Toolkit starts a Chrome process, it adds that command line option, with the hash of your locally generated CA.

Source: https://github.com/httptoolkit/mockttp

source: HN