[ORioN63]

mitmproxy is indeed a similar project. It offers a dashboard similar to devtools (no modifying in there though).

You can, however, write small python scripts that have read-write access to the http flow (request and response objects).

I guess it's a more low level tool, because it doesn't provide mocking and other helpful tools out of the box.

[chrisweekly]

mitmproxy (/mitmdump) is awesome and powerful, and is ideal for integrating w/ other cli tools (like lnav) in chained scripts written in your language of choice. highly recommended.