I’ve used it to diagnose (and work around) webhook problems between third-party applications that are supposedly compatible.

One that sticks out in my mind is trying to receive Slack webhooks in Mattermost. I was unaware of Slack’s new BlockKit message format until I saw what was being sent. Then I wrote a simple python script to transform the payload, all within mitmproxy. It’s not the most efficient long term solution, but the fact I could diagnose and resolve the issue with a single tool, all within a few hours of first discovering it, was very satisfying.

Here’s the result for anyone interested (warning: it’sa quick hack, not a polished/maintained project)

https://github.com/thinkmassive/mattermost-webhook-slack-pro...

Edit: this doesn’t use TLS at all. I understand that’s probably the primary use case for the tool, but I thought this was a cool example of other ways it can be useful too.